thank you okay so in this session we're going to revise unit one the IGCSE physics this works for Cambridge and at Excel by the way I'm often I often just use Cambridge but this works for Cambridge and Excel they're almost identical syllabuses and curriculums so it doesn't matter this is for 2023 because the syllabus has changed in 2023. right so this is the first unit General Physics and a mechanics we'll first start by talking about the update and every time we revise we'll talk about the update of syllabus that was updated this year 2023 there are certain topics that have been removed certain topics that have been added and in unit 1 in General Physics the primary thing that has been removed is pressure not all of it just the barometer and the monometer so if you're watching any of the older videos or if you're studying through older past papers if you see any mention of a YouTube manometer like this or a barometer that looks like this these have been removed from the curriculum to unit 1. all right very good there's nothing that's been added to the first unit that's new so let's get started one more point point out yeah IG students this is for a full IGCSE syllabus but if you ever see this symbol on something that I'm explaining it'll either be at the top of this page or to the side next to a specific route or anything this is the extended version of the syllabus for the full IG your 9 students will not need to study this of course students will not need to study this but nonetheless just listen to it nonetheless why because it'll help you understand stuff better it actually gives you a better idea with the exception of in this particular unit the unit of momentum the chapter of momentum this is a completely different topic which you have not touched at all you can safely skip that part as we're explaining things now in hindsight I should have probably pushed it to the very end of the video let's get started so what are we studying today in unit one it's very important to keep in mind what chapters we have and what things we're going to discuss in study there's measurements in density so mass volume like how do we measure these things how do we calculate density and so on speed and acceleration very important topic very common topic as well how do you calculate speed speed time graphs distance learn graphs acceleration and so on introduction to forces as in the different types of forces that we have like friction and weight and air resistance in their details and how we calculate the resultant forces hooke's law which is just Springs so when you apply a force on a spring it causes it to stretch and the rules behind that Newton's Laws of Motion which you probably are familiar with when it comes to if you apply a force on an object it will either accelerate or decelerate or change direction but if the force is zero stays at rest it's a very common thing along with other examples of motion momentum this is only for the extended students pressure force over area moments which is defined as the turning effect of a force and energy work and power so kinetic energy gravitational potential energy chemical and so on and we'll finish this up this is a continuation of energy work and power but sources of energy which involve power stations and how we generate electricity let's start with the first chapter let's talk about measurements first you have different quantities you should be familiar with all of them these are the important quantities right now length time and mass they're measured in what we call an s i unit which is short for system International and forgive my butchering of the French language and pronunciation but it basically means International System against standard units for everything length is in meters times and seconds masses and kilograms temperature electric current are in kelvin and ampere but these are unit 2 and unit 4. we'll discuss the difference between Kelvin and a Celsius next time or like later there are lots of prefixes when it comes to these units the three most common prefixes are kilo so one kilometer for example is one thousand meters which is divided by 100 so 2 centimeters is 0.02 meters do you see what I did I divided by 100. and mainly so let's say you have a time of 35 milliseconds so you divide by a thousand I have a 0.035 seconds you need to know how these prefixes work all right there are other prefixes as well like Mega which is very rare but that is times a thousand thousand or times one million Etc and micro which is divided by a thousand thousand but to be honest they're very rare they've only ever showed up like once or twice in the past papers before and that's for extended students do not for students so we're going to move on from prefixes and actually start talking about something important you have many different quantities that you should be able to measure focus on the measuring instruments and measuring techniques that he loves to ask you about whether it's in a multiple choice question or in paper three or four or in paper six the pendulum or the period of an oscillation the time of one oscillation as in when the object or like a pendulum goes back and forth is called the period to measure the time of one oscillation accurately you need to measure the time of let's say 10 oscillations so let's say this is 3.43 seconds okay for example this is not really 3.43 this is three minutes 43 seconds and 0.75 but then you divide it by the number of oscillations so the way you get the period is by taking the total time of 10 20 30 oscillations and you divide it by the number of oscillations most common questions use either 10 or 20 or Solutions then what about Mass Mass is measured with a balance it's not really that hard but you have different types of balances a top pound balance where you just put stuff on it and it just gives you the reading a spring balance where you hang something on it and it stretches to give you the reading this is also what we call a Newton meter because it can help us measure forces or weight like we can attach it to something and pull it and this gives me the value of the force and finally the beam balance it has many different shapes but the basic concept is this you have two trays you put an object on one side and you put a load on the a other side and you compare them this is very good for comparing things it's not very good for measuring things upside then how do you measure the mass of a liquid that's a technique that you need to understand the problem with measuring the mass of a liquid is that liquids have mass and their containers also have mass so for example here this is an empty measuring cylinder with a mass of 200 grams if you only want the mass of the liquid you'll subtract these two values from each other 250 minus 200 which is 50 grams just 50 grams so this gives me 50. so mass of the full container minus the mass of the empty container gives you the mass of the liquid [Music] very good next let's talk about length we have three measuring instruments for length actually Four honestly but three at least here a metered rule this is very good for distances up to one meter so if an object is up to a meter long so about this big yeah you can just raise a ruler just mention rule or ruler and that's fine if you have any longer distances 2 3 5 10 100 meters 200 meters we use what we call a measuring tape or a tape measure this is really good for very long distances and if you want to measure very thin objects like a thickness of a sheet of paper or the diameter of a wire or the thickness of a coin like this is a very common questions you use a micrometer you don't know you do not need to know how to use these instruments you just need to know which instrument do I use when that's all however there are a couple of techniques that you need to keep in mind the first of which is how do you get the thickness of a sheet of paper if you don't have a micrometer like if you do not have this and I only give you a ruler how do you measure the thickness of a sheet of paper well you get your full stack of papers like if you get your entire book and then you measure the thickness of all of these stacks of paper at the same time so let's say you have 100 sheets of paper you measure the thickness of all of these and it is about two centimeters then the thickness of one sheet is two centimeters divided by a hundred sheets which gives you 0.02 centimeters all right very good finally how do you get the diameter of a ball the problem with spherical objects in general like or circular objects is that they don't have an edge so if you put them next to a ruler your eyes can't really extend this virtual line in the air and get the value accurately you will almost always get this value wrong not completely but slightly wrong the way we measure any spherical or round object the diameter of which at least is to put it between two flat blocks blocks of wood the blocks of metal blocks of plastic choose whatever blocks you want just stick the object between between these two blocks check the length here check the value of the length of the first block the value of the length of the next plot and find the size of this Gap so what's the diameter of this ball it's going to be about two centimeters very good so that's how you measure the thickness or length these are just special techniques finally when it comes to volume it honestly depends if you're measuring the volume of a regular solid like this cuboid this blocks over here it's simply length times width times height again the volume is length times width times height that's a problem right no problems at all but keep in mind the general rule that we use to measure volume or calculate volume of a regular shape is the area of its base times height So when you say length and width you're actually getting this when you say length times width you're actually getting this all right so that's the area of the base times height times this works with a cylinder by the way if I tell you hey the cross-sectional area of this cylinder is 10 centimeters squared and the height of this object is two centimeters what's the volume of this cylinder so it's 10 times 2 which is 20 centimeter cubed and that's the unit of measurement of volume so meter or centimeter field if you're measuring the volume of a liquid just use a measuring cylinder this also works with anything that flows like a liquid think sand sugar rice like anything that flows you can get an approximate volume of that as well using cylinder but if you want the volume of an irregular solid object think your keys for example clear in irregular shape you cannot calculate their volume using your regular rules so what do we do we get the volume here this value should be about let's say 50 60 70 75 that's your initial volume of the water put some water in the cylinder and then slowly and gently drop the object into the water to avoid splashing so what will this value be so that's 100 110 120 125. the difference between these two readings is going to be the volume of this rock so the difference between the two so 125 minus 75 is 50. is 50. very good so how do you get the volume of an irregular solid or some water in a measuring cylinder measure the initial volume put the object in measure the second volume calculate the difference between the two counts next any of these measurements could involve small amount of error like there's always a little bit of a mistake but there are three mistakes that you must keep in mind the zero error which is when the instrument doesn't start at zero for any reason like again maybe you made a mistake maybe you broke the ruler maybe it's your favorite ruler when you're three years old and you don't want to let it go because it has a picture of Iron Man on it or something I'm not gonna judge but how do you measure the length of this object you take the initial reading so this is 5.2 and then you take the final reading in this case it's 8.1 and you calculate the difference between these two ends so 8.1 minus 5.2 it should give you 2.9 centimeters obviously because the ruler is in centimeters very good Parallax error that's when you don't look at something properly you're supposed to look at an instrument perpendicular to the a to the scale so you're supposed to hold this ruler and look like this perpendicular to it but you're not supposed to look at it above or below it at an angle that's called Parallax you're looking at the different angle to where the object's surface actually is is called Parallax and let's call The Parallax error so what's The Parallax added about so what's The Parallax error this is you're not looking right how do you fix it by looking perpendicular to the scale am I looking perpendicular to the scale good very good next the meniscus sir now this is not very common but you will see it a lot in paper six by the way and sometimes in paper too like he enjoys that the surface of the liquid is never properly flat like this no no it's not straight it's not horizontal the edge of the liquid always you know climbs up the container it's in you might ask what's the problem so what what's the problem there is no problem there is if you were to look perpendicular to the measuring cylinder to avoid Parallax air like you should you will end up seeing two readings that are the value so you're going to see a very thick surface and you won't be exactly sure which one is it the upper surface or the lower surface because of the curvature of the water so between 40 in this case this is going to be 40 cam 46 and this is 48 because every square or every division here is 2 170 squared I mean which value is correct ah what do you guys think 46 or 48 46 thank you you look at the bottom of the meniscus we look at what we call the bottom of the meniscus not the top because the top is just a drop of water and finally oops clear the word let's talk about density density is quite simple it's just Mass over volume it literally defined as the mass per unit volume of a substance and that's over the body the more dense an object is the smaller and heavier it'll be thick metals the less dense an object is the bigger but lighter it'll be so this could be a 10 kilogram dumbbell whereas this could be a half a kilogram balloon so the more then something is The more mass it will have and the smaller the volume the less dense it is the less Mass it will have and the larger the volume okay the equation is just Mass over volume this is the symbol that we use for density we're going to use it later and this is mass and this is a volume none of this is actually challenging or difficult now the units in clusters could either be kilogram per meter cubed or grams per centimeter cubed it depends on the question just be careful when you're calculating density I have three things to point out number one density affects whether or not objects sink or float so if you see an object in water and that object is floating it's less dense than the liquid itself and if the density of the liquid is 1000 kilogram per meter cubed that's expensive water for example then this object that's floating has to be less than a thousand could be 900 could be 800 could be anything I'm not talking about weight and I'm not talking about Mass I'm talking about its density and if you have an object that has sunk into this water this is more dense than the liquid so it's more than a thousand could be 1010 could be two thousand could be three thousand I don't know but it's more than a thousand it's more than the density of the liquid Point number two same material means same density so if an object or you're comparing objects of the same material then they have the same density the only thing that can affect density is temperature or heat the higher the temperature of an object the less dense it will become because as we'll study or revise in unit 2 in thermal physics when you heat something its volume increases but the mass stays the same so the density is affected that's what causes convection but keep that in mind the only thing that affects density is a is fun is temperature okay very good do you have any questions so far nothing good moving on so calculate this example very quickly 500 gram block it has a length of 10 both 2 and a height of 5 for example what's density this is quite simply Mass over volume so that's 500 over 10 times 2 times 5. so 500 over 10 minus 2 times 5. this gives you an answer of five but wait five what if this is in grams and this is in centimeters and centimeters and centimeters you have five grams per centimeter cubed moving on oops the so-called speed and acceleration very quickly what is speed distance over time speed is nothing more than distance over time it's either meters per second kilometers per hour depending on the question carefully the units if I ask you to calculate average speed it's the same thing it's distance over time it's just total distance over total time so solving this example very quickly speed is distance over time oh we need to read it first a car travels 100 kilometers that's great we have the distance the high speed is 90 and the low speed is 30. this is a question from paper uh from paper two or paper one multiple choice the journey takes two hours what's the average speed I don't care about the values of speed that he's given me he's given me distance and he's given me the total time so it's just distance over time so 50 kilometers per hour next now before we move on some quantities that we study will be scalar some of them will be vectors scalars are quantities that have only magnitude by length time and mass and such and vectors have both magnitude and direction why are we mentioning this here because speed is a scalar quantity we only care about the value however if an object is moving and you want to add to its speed like in meters per second or kilometers per hour its direction we call it velocity this is a vector because it is described with the value and the direction so it's 10 meters per second no it's 10 meters per second to the right for example for most questions this won't matter too much it will matter when we talk about forces next up let's talk about acceleration acceleration is defined as the change in velocity or change in speed over time or rate of change in speed it's calculated using change in velocity over time we often write this down as Delta V over t although sometimes it will be written as V minus U over t the unit of measurement of acceleration is meters per second squared yeah there are three cases of acceleration that you need to keep in mind if an object is speeding up speed is increasing 10 20 30. this is called positive acceleration or just acceleration that's called acceleration speed is increasing if an object is slowing down 30 to 20 20 to 10 10 to 0 like he's losing 10 meters per second every second this is called the acceleration or negative acceleration all right and finally back this is for the extended folks if an object is moving and then it changes Direction it's moving at 10 meters per second or kilometers per hour and it changes Direction it has the same speed so same value it is still accelerating why because the direction has changed and if the direction changes that means this velocity has changed and if the velocity changes but this is called acceleration we do not calculate acceleration due to change in Direction we don't calculate it huh it's not calculated but we just need to recognize it like hey you're going in a circle you're changing direction movement goes to the right are you accelerating yes you are good uh this is uh an extended question so the question is a ball is dropped from tall building it takes 3.2 seconds to reach the ground and falls with an acceleration of 10 meters per second squared calculate the speed that the ball hits the ground with here's the rule change in velocity over time what have I given you speed is 3.2 times 3.2 and the acceleration is 10. so what's the speed make it the subject so change in velocity or speed is acceleration times time the acceleration is 10 times 3.2 this gives me 32 meters per second so easy peasy some people say lemon squeezy I don't know why I don't like it Japanese let's talk about graphs you have two types of graphs distance time and speed time graphs if you're given a distance time graph the things you can simply say are A to B you're moving at constant speed because the line is straight it's going off the distance is increasing this is not speed huh this y-axis is not speed this is just this and B to C you're moving at constant wait are you moving are you even moving from B to C no your distance is not changing four seconds you're at eight meters away from the start at five seconds you're still eight meters away from the start at seven seconds you're still eight meters so we're going to start you're not moving your address yeah the slope of this line how steep or less deep this line is represents the speed so you can easily calculate speed using distance over time it's nothing special next very good moving on speed time graphs are a lot more nuanced and they've got a lot more detail so from A to B the speed is increasing so it's acceleration from B to C the speed is not changing this is not a trust this time around the speed is not a changing so this is moving at constant speed but I see today it's a decelerating the speed is decreasing okay the slope of this line like how steep the line is upward down represents the acceleration of the line so the steeper the line is the more you're accelerating and the less steep the line is the less you're accelerating you're still accelerating but at the lower value if I were to compare the accelerations of a b and c d yeah sure it's deceleration but again CT is decelerating faster or more than a b because it changes the same speed over a shorter time or you could simply say the line is steeper how do you calculate distance from a speed time graph very common question you get the area under the graph I know a lot of you would still default to hey Mr Speed distance over time so therefore distance equals speed times time you are factually correct but most of the time it does not work when you want to calculate distance from a speed time graph because this rule only works if you're moving at constant speed it only works if you're moving at constant speed here the speed is not always constant so it's area under the a graph all right very good let's try let's try to solve this let's try to see if you want the area of a triangle what's this it's half times base times height this is the area that I'm talking about if any of you are shy and you're not asking me questions here this is the area we're talking about this is the area of a triangle so if I were to only ask you to calculate the area of a b you would say half times base which is 4 times height which is eight so half times four times eight this would give you 16 meters because the unit here is in meters very good so go ahead and calculate the total distance hmm I look at the total distance you can either split this into three shapes so you have a triangle here a rectangle here and a triangle here or you can get just get the entire area I'm going to skip and use this entire area I've already revised what the rule for a triangle is that's half times based on its height and a rectangle is that's just Baseline type but what if I wanted this entire shape this is a trapezium and the way we calculate the area of a trapezium is base one plus base two over two times height so base one which is nine this entire base is nine plus base 2 which is this thing over here from B to C from four to seven seven minus four is three so nine plus three over two times what's the height eight nine plus three over two times eight which is 48. meters all right and how do you calculate average speed this is like a follow-up question from the very beginning of this particular chapter in points to get average speed it's total distance over total time What's the total distance 48 What's the total time nine so 48 over 9 is 5 point how many significant figures should I write my answers to an IGCSE well just write it to three just write it to three significant figures and give yourself a rest three meters per second now as we already mentioned before the slope of the line represents the acceleration so the steeper the line is the higher the acceleration the less steep the line is the lower the acceleration a negative sloping any negative acceleration it means negative acceleration that also means deceleration and then finally oops what if the line is curved this is an extended part I seem to have forgotten to add these or they're not showing up so what if the line is curved then it's not constant what's not constant acceleration if the slope of the line is increasing like it's getting steeper we call this increasing acceleration if the slope of the line is decreasing and it's getting less steep this is called decreasing acceleration if the slope of the line is increasing but the line itself is going down this is called deceleration because speed is dropping but this line is becoming steeper and if the line is becoming steeper the deceleration is increasing you know over here the deceleration is decreasing so you can get a better mental idea of what that physically means what that physically means increasing deceleration means you're pressing the brakes of your car or your bike slowly at first to slowing down a bit but then you realize like you're oh my God I'm going to smash into that tree or wall or dog or can you smash the bricks and you break hard here you break hard initially in decreasing at these options you break hard initially but then you realize hey you're breaking too hard and let the brakes go a bit we're still breaking you're still slowing down but you take a longer time before I move on to forces there was one question so Delta V is speed yes Delta V in the previous equation for acceleration change in velocity Delta V that the velocity is speed so speed is acceleration times time courses a force is a pusher report nothing special here but the force is a vector to the extended box which means it has magnitude and Direction so the direction is going to be important when you apply a force on an object it could you know change its shape change its size you know I could I can grab I have a hat here somewhere yes cap I can take this object and I can fold it and I can squish it and I can bend it so I can change its shape and size no problem I can take this ruler and I can bend it I'm gonna break it up but it can also change the speed and direction of motion of the object the velocity of an object essentially a force cannot change Mass it's a very common multiple choice question words cannot change pass now there are certain courses you need to recognize at least in terms of name there is a resistance there is friction these are both resisting forces if you're moving through the air it slows you down if you're pushing an object on the surface the roughness of the surface resists you it's called friction there is weight which is a pull of gravity we'll discuss this a bit more now there is up thrust which is the upward force of the water on the object so it gets pushed up it floats there is tension which is the name of the force in a thread or a rope or a cable so if I have a rope or a thread like this and I stretch it the name of the force that's in the Rope as it's being stretched is called tension is foot engine that's all just the name and then there's normal contact all right your hand is making contact with your phone that's called normal contact okay okay next let's talk about friction a little bit more detail what is friction it's a resisting Force nice to slow you down it's the force between two surfaces especially when it comes to solid objects due to the roughness the rougher the surface is the greater the friction you can decrease friction by lubricating the surface like dropping some oil or water on the floor or by making the surface smoother whenever there's friction there's also heat that's produced which is very common like if you're feeling cold and it's dead winter and you just rub your hands together you feel warm friction is also called drag so if a car is moving through the air air resistance is just another form of friction or if you're swimming in the water and the water is resisting you that is called friction you could call a drag a resistance friction it all works now a very important force is weight weight is defined as the force of gravity or the gravitational force on an object gravity always affects any object with Mass so this pen I'm holding and drawing with has mass my phone has mass my laptop I'm not going to lift my laptop as well as mass right although I've dropped oh God anyway anybody who knows me knows how you know aggressive I am with some of my technology iPad throwing gang here anyone anyone okay any good jokes aside so it's the force of a gravity you will never forget you will never will but what is mass it's the amount of matter in an object so mass is simply the amount of matter in an object you calculate Weight by using this equation W equals mg weight is equal to mass times what's g g is short for gravitational field strength gravitational field strength it's how strong a planet's gravity is we'll emphasize this more when we hit space physics as well but the value of G on Earth is 9.8 Newtons per kilogram now one of the changes that wasn't mentioned in the early syllabus document like the first document we saw that was just a snapshot of the document was this they didn't mention it explicitly in this in the document but they have changed it in the past papers from now on the value of G is going to be 9.8 as in every one kilogram is not going to have a weight of 10 Newtons like we used to have all of the mark schemes in the older past papers will have this as 10 that's fine anything before 2023 will have this as 10. from now on it's 9.8 which rounds up to 10 so it doesn't matter next how do you calculate the resultant Force simple if two forces are in the same direction uh 10 Newtons and 20 newtons their combined force or the resultant force is 13 equals if the forces are an opposite directions so 10 Newtons and 20 newtons to the left you don't add them you subtract them so this will give you 10 sorry what was I going to say 20. 10 Newtons to the left 20 minus 10 is 10 to the left but then things get a bit more complicated when forces are not in the same direction so if this is a 10 Newton Force to the right and this is another 10 Newton Force to the right at an angle of 90 degrees to each other the resultant force is going to be something in between and somewhere in between them we don't know the exact values but I can't just add them anybody who studies any kind of advanced math foreign ometry and so on will tell me that there is a method that you can use to calculate this and use the Pythagorean theorem the Pythagoras theorems anyway we're not going to calculate it here we're going to draw what we call a vector triangle or the head to tail method to find to find the resultant Force to find the resultant of course step one this is being very succinct and brief you get your ruler and you draw this diagram to scale to scale which means that everyone centimeters let's say is one newton so on my board on my screen I'm going to draw a 10 centimeter line to the right because this represents this 10 Newtons here so 10 centimeter line to the right actually let me use the line tool so it actually looks like a line whoop here's 10 centimeters this is to scale at least to my scale because it's on the screen and then from the end of this line you draw another 10 centimeter line at 90 degrees to it here so let's label these this is a 10 Newton Force to the right this then you can force to the left it's called head to tail is because you draw the head of this Force attached to the tail of the next that's why so we just call this the triangle method or a vector triangle where is your resultant the resultant is going to be the line that joins the start and the end of your diagram this is your resultant this is your resultant r if you've drawn this to scale you can measure this with your ruler you probably don't see me right now but I've got my ruler on my screen and that's 14 centimeters since I'm using a scale of one centimeter to one newton yeah but this is a 14 Newton resultant Force what about the angle the direction remember vectors have to have Direction we almost always measure unless the examiner tells me otherwise the angle between the resultant line resultant force and the horizontal this angle over here what do you use you use a protractor somebody has mysteriously removed but I know the angle off the top of my head because you know this is simple geometry this is going to be 45 degrees so my response to what's the direction is 45 degrees to the horizontal 45 degree is 2D horizontal right very good before I move on questions okay so no questions excellent this is a good question if the forces are not at 90 degrees then what do you do let me clear all of this out because that's a very good question what if these two forces were at and ignore this diagram for now what are the forces that we're discussing were let's say a 10 Newton Force to the right and another 10 Newton Force at an angle of your choosing let's say 30 degrees you'll follow the same Steps step one you draw it to scale let's say one centimeter is one newton so you draw the first line always draw the easy ones the horizontal lines the vertical lines so I'm going to draw a 10 centimeter line here this might not fit on my screen but I'll do my best and then and then we draw this at the angle of 30. now what do I mean let me erase this all right [Music] I'm just drawing dotted line so you know what I'm doing if I put my protractor here I will measure a 30 degree angle from the horizontal and then from here we draw the 10 centimeter line there we go so it's the exact same steps to read but what do we do we measure this angle first finally since we are drawing this to scale [Music] this line is your resultant and this is what you measure I'll change the color to Bluebell and oh gosh this is going to be a big line big line and it's about 18.4 centimeters so the resultant is 18.4 Newtons and what's the angle we measure this this should be about I I'm really not sure but let's say halfway between the two or something at 15 degrees so we're going to see the direction is 15 degrees to the horizon there we go it will be 14. like the previous example will be 40. if you tried using Pythagoras and it's not 13 it's 14.14 or something like 14.14 yes it'll be 14. let's talk about mutants loss of motion Newton's first law an object at rest will remain at rest or in a constant state of motion unless acted on by an external resultant Force blah blah blah blah blah I'm not going to memorize that but what I want you to memorize is this if an object is moving to the right and the resultant force acting on it is also to the right this will accelerate if an object is moving to the right but the resultant is to the left and I want you to understand what I mean by resultant this means there are forward forces that are backward forces and after you subtract them this is what's left and in this case the forward driving force is more than the resisting forces here the resisting forces are more than the driving forces this will decelerate and if the object is moving to the right but the force is sideways the object will rotate it will turn it will change direction so basically if there is a force the object accelerates in all of its meanings speed up slows down changes Direction this is the most important part of it all if the resultant force is zero the forward and backward forces are equal what will happen if the object was initially at rest meaning it's not moving it stays at rest it doesn't move but if the object is moving it is moving then the object moves at constant speed the object moves at constant speed speed does not change that's very important this is this is the most important part so if I tell you that the object is moving at constant speed you can say that the resultant force is zero if I tell you the resultant force is zero it will move at constant speed both of these arguments are extremely important Newton's second law is just f equals m a force equals mass times acceleration however there is one important thing here besides the formula and using it the force in this equation is the resultant force it is not the driving force it's not the resisting Force it's the resultant so in an equation for example or as an example I tell you hey here's a car the driving force on that car is 100 Newtons forward but there is a resisting force of 10 Newtons and this car has a mass of uh what cards are supposed to be heavy but let's just say 600 kilograms calculate the acceleration so what do I do f equals m a so if I want the acceleration a equals F over m the force that you substitute here is not 100 and it's not 10 it's their difference it's the resultant so this car will barely accelerate by the way like I shouldn't have used 110 as my forces because that's nothing virtually nothing 0.15 meters per second squared that's your answer but off the top of my head I like to drive slow under the speed limit way under the speed limit I mean I'm driving so slow below the speed limit I'm getting a ticket for moving slip I hate that when people do that by the way now you drive like imagine I'm driving in the middle of the road five Lanes Street on a highway and you're rushing and then you've got this you know I don't know what they're doing watching YouTube or something or playing Candy Crush on their phone and they're driving slowly in the middle of the road it's frustrating anyway if you ever learn to drive folks you wanted to go slow stick to the lane on the very far end to the right example like in our case it's we drive to the right if we're slow and anyway foreign just remembered I need to get the driver's license soon uh international driver's license okay nothing nothing anyway this is literally a quick example a force is given a resultant force of 4500 Newtons is given with a mass of 900 calculate the acceleration there is absolutely nothing special here acceleration is force over Mass with an actual proper value of force acting on this car so it can accelerate this will give you an acceleration of five meters per second squared oops yeah finally there are two cases of motion that you need to keep in mind and memorize case number one if an object is falling in a vacuum there's no air resistance you follow the constant acceleration of 9.8 meters per second squared which is the value of G but if you're following through the air then there is air resistance acting on you all right the smaller the size of the object the smaller the air resistance and the larger the size of the object the greater the air resistance because that's one of two factors that affects air resistance size being the first second interval that's right we'll see in a bit so the smaller the area the cross-sectional area of the object the smaller the value of the air resistance acting on when an object is falling through air it goes through three stages of motion stage one when it's just dropped it falls with a constant acceleration because there's only weight acting on it but then stage two as it continues to fall the weight is the same but there's a little bit of air resistance so as the air resistance which I will call R increases the resultant Force which is called f will decrease I'll give you an example if this is a hundred and this is 10 the force is now 90. before the force pulling you down was a hundred as the resultant Force decreases the acceleration decreases eventually this continues to happen by the way gradually and eventually the air resistance increases so much that it becomes equal to your weight so the weight is now equal to air resistance the resultant force is zero they cancel each other out and you follow the constant speed you can follow at constant speed we call this terminal velocity so this is the second thing that affects air resistance the faster you're moving the greater the air resistance acting on you if I draw a speed time graph of this motion it will look like this accelerating accelerating with the acceleration decreases decreases decreases and then this is your terminal velocity if you open by a parachute I I don't want to call this stage four because you don't always open a parachute actually if you're skydiving you should always open your parachute in the end but let's assume the parachute doesn't open let's just say oh let's not go dark here and you open your parachute for the just the moment and for the next few seconds after you open your parachute the air resistance is now greater than your weight you do not move upwards you just slow down until you reach a new terminal blast yeah if an object is moving in a circle the resultant force acting on the object must be towards the center of the circle always even if I'm saying you're moving at constant speed you should be but your velocity is changing so your Force the result will force acting only is towards the center of the shirt that's causing you to turn as the object turns and goes around the circle if it's either number one moves too fast or number two it has too much mass or number three the circle's radius too small if any of these happen the force that's pulling you towards the center will not be enough to keep you in a circle in order to stay in a circle you need a force to keep you sorry my nose is blocked in order to keep you in a circle the force that you need should always be towards the center of the circle move too fast this force will increase or if you're too heavy like a big heavy truck this horse will increase or if you're trying to turn a very sharp U-turn this force will increase so much that your car the friction uh whatever force is trying to keep you there won't be able to keep you there so you leave the circle you will always leave the circle in a direction that is tangent to the circle at the point of release so if my car actually is here it shoots this way if my car is here it shoots this way and so on all right next momentum momentum is quite simple it's just mass times velocity there's nothing special about it don't don't overthink it momentum is mass times velocity a lot of people try to think too much about this it's the product of manvi the units either kilogram meter per second or Newton Second you'll you'll find out why it's in second in a bit but you can use momentum to calculate force the equation we use to calculate force when it comes to momentum is change in momentum over time this also means that if I ask you to calculate change in momentum this will be force times time this will be force times because time goes up Mr tub what do I use f equals m a or change momentum over time depends on the question okay if the question literally gives you masses and velocities and momentum and such just use that if it gives you acceleration just use the other it's not that hard remember folks always hydrate my biggest mistake in life actually have a lot of the missile uh always remember to hydrate finally when it comes to momentum there's one more quantity that's called impulse sorry impulse is literally defined as force times time impulse is literally defined as force times time it's nothing else about but remember on the previous page or slide we defined Force as change in momentum over time but then when we made force times time a subject it was equal to change in momentum this means that course times time which is impulse is also equal to the change in momentum which is basically momentum assuming your initial momentum was Zero this is why the unit of measurement of impulse which is Newton's second is also the same as the unit of measurement of momentum which is kilogram meters per second because they're just the product of mass and velocity or the product of force and time it's the same thing yeah a very important law when it comes to momentum is the law of conservation momentum but yeah let's solve this example really quick uh driver accelerates at a force of 13 Newtons acts at a 900 kilogram car for 10 seconds calculate the impulse whenever you solve questions I want you to do what I do what do you do Mr I underlined the numbers sometimes I even just write letters on top of these numbers to give me a hint like what do I have I have Force I have time I have mass what do I use for impulse well I know that impulse is either force times time or change in momentum I have force and time so impulse is force not start so 30 times 10 which is 300. minutes then he wants the change in velocity due to the inputs now do not go back and think of acceleration what's the relationship between change in velocity and impulse well I know that impulse is change in momentum and momentum is mass times velocity I have the impulse and I have the mass I do not have the Velocity that's what I want so the velocity is the impulse divided by mass which is 300 divided by nine one this will give you a recurring value of a 0.33333333 so 0.333 meters per second what's the law of conservation of momentum it's defined as the total momentum of a closed or isolated system is always conserved or total momentum before equals ultimate but in order for you to understand what I'm talking about here's a quick non-numerical example I'm playing pool or Billiards I hit the ball the first ball is now moving with a velocity of 10 meters per second I'm not going to calculate anything it's just with the sake of the question and this ball is stationary this is before they hit each other bam they hit each other after the Collision both of the balls stick together and they roll together until they fall into the hole and then I lose the game because I dropped the white wall as well because I'm an idiot and I can play cool to save my life but how do we solve this kind of question like how do we find out what is the velocity after they collided this can only be solved if we calculate the momentum of each ball separately before the Collision and we add them and we can calculate the total momentum of the balls after the Collision like if they've stuck together that's double the mass times velocity and these two should be equal like the momentums of these balls before the Collide should be equal to the momentums of the walls after they collide this gives us following example of mass a or 0.25 and here's my hint before I continue reading if the question has not sketched this case it's in front of you sketch it yourself I don't want a detailed diagram just draw a quick sketch of before the collision and after the Collision please it helps a lot have a ball 4.25 kilograms what's next moving at 20 meters per second that's great it's a stationary ball so that's another ball that's not moving I'm just going to write X so I remember it's nothing of mass 0.025 it's a lot lighter maybe I could have drawn it smaller after the Collision so that's before after the Collision they stick together okay okay so they're stuck together so what's their Mass okay if they're stuck together we add their masses so 0.25 plus point zero two five this gives me 0.275 we now have the mass of both of these balls together and they're moving at a velocity that I don't know this is before and this is after what's the momentums first calculate the momentum of the ball before a before the Collision well that's easy momentum of all a is mass times velocity that's a and that's B uh 0.25 that's the mass times velocity which is 20. this gives us 0.25 times 20 which is 5. kilograms meter per second now remember total amount and before equals total momentum after we're going to need this for the next part calculate the speed of the balls after the Collision okay so how do we solve this before equals after What's the total momentum before well this was five plus this isn't moving there are two separate objects so this was five this is zero there's nothing else before the Collision equals what's after mass times velocity I have the mass 4.275 but I do not have the Velocity I'll just label it as V find V I'm sure you're all professional mathematicians by now but you must be way better at math than me so 5 divided by 0.275 this gives me 18.18181 and that's a very curious number 18.2 meters per second that's momentum does anybody have questions about momentum nothing we could we good excellent let's move on book hooke's law or some of my students like to call hooky's law because he's such a hookie I know anyway moving on oh my God that was so cringe before we talk about hooks law let's define a few quantities first here's a spring this is called the original length of the spring here's the spring after we attach the load which is the force that's going to pull the spring this is the total length of the spring or the new length of the spring or the stretched length of the spring it has many names all right how do you calculate the extension the extension is the difference between these two lakhs so I'm just going this call this L2 and L1 so it's L2 minus L1 next hooke's law states the following an object will always be sorry the extension I almost defined Newton's Laws brain fart moment extension is proportional to what extension is proportional to what load or Force when I say that they are directly proportional this means that if the force increases the extension increases as long as the elastic limit is not crossed so what's the elastic limit it's the maximum Force that the spring can handle and still go back to its original shape so if you stretch your spring Let It Go it goes back to its original length or shape that's it now from hooke's law we have a very simple equation it says that force is equal to spring constant times extension f equals KX the spring constant has a second name we sometimes call it the stiffness of the spring how stiff a spring is if you want to calculate it K is equal to F over X nothing special here just keep in mind the units if the force is in Newtons and X is in centimeters for example then it's Newtons per centimeters or Newtons per millimeters and so on very quickly let's solve this example here's a graph use the graph to calculate the original length of the spring oh wait how do I know the original length it's the length of the spring again it's the length of the spring at the load of zero like before it was stretched so this is the length of the spring before it is stretched five so it's five centimeters so that's eight next the extension of the spring at 20 newtons from 20 you go up the graph line hit the graph line and then you check what the length is the value is not eight remember you want the extension the current length is eight the original length is five so the extension is three centimeters and this is about for the extended folks what's the spring constant well k equals F over X I already have a value of F and X that's ready from the previous question if the force is 20 newtons and the extension is three centimeters we just got that so 20 divided by three gives you 6.67 Newtons per centimeters okay yeah Crusher this one's easy uh if I get a sheet of paper somebody should try to write in the street here if I get a sheet of paper and I punch it nothing happens but if I stab it trust me I have no homicidal Tendencies okay if I stab it what's going to happen the pen is going to go through the paper why what's the difference why what's the difference this very small tip all right it's very small okay it's a very small area it's a very small area and if the area is very small the pressure of that Force increases allowing it to cut through objects allowing it to cut through objects okay that's what we call pressure it's the concentration of a force over a specific area so it's simply defined as Force per unit simply Force per unit okay of course over E equals F of great if the unit of force is Newton and the unit of area is meter squared the unit of pressure is Pascal if you call it Newton per meter squared that's fine if you use Pascal that's also fine some questions often use Newton per centimeter squared but that is not going to be Pascal what about in liquids in a liquid the pressure is not dependent in force on Earth it depends on how deep you are in the liquid and how dense the liquid is the greater the height of that liquid or depth the reason we say depth and not height is because we measure it from the upper surface to the lower surface go over here to here right now it doesn't it makes no difference but it will in a bit just just give me another Slack so the deeper the liquid is the greater the pressure let's go that makes sense because what do you mean it's proportional to density if I have two measuring cylinders that are both filled to the same level same height same height same height but they're different liquids this is water let's say with the density of 1000 kilograms per meter cubed it's the density and this is oil let's say it has a density of 700 kilograms per meter cubed off the top of my head both of them have the same height but both of them will not apply the same pressure the water will apply more pressure at the base of its container or on the floor then the oil because it's literally heavier it's more that this is why when we calculate the pressure in a liquid the equation is rho GH the equation is rho GH where rho is density ah remember earlier in the session I told you this is going to be important G is 9.8 and H is the depth uh keep in mind a friendly reminder again most questions in the mark schemes uh from 2022 and before that will have the value of G set to 10. so if you're practicing at home and you're solving past papers it's not 9.8 it's 10 it's fine but starting this year the value of G is 9.8 keep that in mind yeah this the final point I want to make here which is very important the pressure of a liquid is not affected by the area of the container give me a thin container give me a thick container it does not matter the cross-sectional area does not matter give me a wave like a container with a different cross-section area give me a wavy container it still doesn't matter I wish I had the I wish I had the you know a stream deck because because this moment like needs a meme doesn't matter I was like oh I think it was John Cena I think it was anyway anyway moving on last thing when it comes to pressure under water has an extra detail about it when you go deeper the deeper you are underwater the more pressure acts on your body you go and say yeah I know that because there's obviously more water there's more depth that's great obviously and it's harder to breathe obviously because there's more pressure acting on your body and therefore you know your lungs can but anyway the greater the pressure but the pressure acting on you is not only due to the water if the water applies the pressure of let's say 20 000 Pascal on you because of this height the pressure acting on your body at this level is actually 120 000 Pascal why because the air itself also has pressure we call this atmospheric pressure now you don't memorize the value of this atmospheric pressure but it's about a hundred thousand Pascal or one times ten to the power of five percent so when you're underwater the total pressure acting on your body is due to the sum of the atmospheric pressure and the liquid pressure so both just one of them both very good now before I go on to moments there were a couple of questions didn't you say that stiffness is the original the stiffness is not the original position of the spring stiffness is just a constant in Springs stiffness is just the constant it just represents how tough the spring is it's not the original position I never said that we call that the original length of the spring and k equals F over X that's when we calculate K the spring constant or the stiffness so when we want to calculate this right nothing absolutely it does all right so it's just this all right now uh oh one more question does the atmospheric pressure apply to the pressure of liquids in the cylinders in the previous slide yes it does but the pressure we calculate here pressure we calculate here is the pressure what due to what the liquid I have not calculated the atmospheric pressure I did not include it what I'm asking you to get is the liquid pressure if I wanted the total pressure I would say total pressure I wouldn't say atmosphere I wouldn't say liquid pressure we have a couple of more topics let's let's go through them very very briefly and quickly because they're not too difficult a moment a moment is defined as the turning effect of a force especially here so if you apply a force on an object and there's a pivot unsaid object and a fixed point on the object applying a force on the object makes it rotate or turn take the stroller I'll hold it from this end I apply a force on the other end it will rotate or turn that rotation or the strength of that rotation is called a moment you calculated by multiplying the force and the perpendicular distance from the pivot so force times this distance over here there are two directions when it comes to moments because a moment is a vector if it rotates this way we call it clockwise if it rotates the other way we call it anti-clockwise or anti-clockwise now there there's a when an object is completely balanced we say it's in a state of equilibrium equilibrium means that the resultant force is zero this means that the upward forces and downward forces acting on the object are equal so they can signature the route and forces on the right and on the left or pointing right in that array but an object in order between equilibrium also has to have a resultant moment of zero this means that the clockwise moment needs to be equal to the anti-clockwise mode so if you have a beam like before you have a pivot here and a force on this side and a force on the other side if at the clockwise or the anti-clockwise moments when you multiply the force and distance their moments have to be the same if this is 10 Newtons for example and 10 centimeters and this is 5 Newtons and 20 centimeters obviously this diagram isn't scale and you calculate their individual moments so it's a force times distance so 10 times 10 this gives you a hundred Newton centimeters the anti-clockwise moment is 5 times 20 for science distance which is also 100 Newton centimeters but it's anti-clockwise it will not rotate clock it will not rotate anti-clock it won't rotate this way it won't rotate that way capish sure it's a capish next let's use moments to solve this example in this question he says the beam is in equilibrium measurement it's equilibrium which means clockwise moment equals F and we're going to use both Rules by the way f is the force of an unknown load R is the force of the pivot on the beam using the information calculate F and calculate r well to calculate f I'm going to need moments because here f is applying a clockwise moment and the hundred is applying an anti-clockwise R has no moment because it's passing through the pivot if a force is acting through the pivot it has zero moments please so step one clockwise moment equals anti-clockwise mode the clockwise moment is f times what's its distance to the pivot 0.2 the anti-clockwise moment is a hundred times distance to the pivot is 0.5 this gives me a value of f of 100 times 0.5 divided by 0.2 and 100 times 0.5 over 0.2 this gives me 250. mutants that's fantastic now this example before I move on this example should give you another hint when it comes to the relationship between force and distance when it comes to moments the closer a force is to the pivot the greater the value of that Force and the further away an object is from the pivot the smaller that Force look at this look at this they're balanced but this force is 250 it's more than 100 because it's closer think of that when you open and close your door the easiest core to open or close your door is the very edge or tip of your door you can use your finger to push and pull the door put something's wrong why because you're very far away from the pivot so your moment is very large thanks to the distance not thanks to the a to the force next what center of gravity or Center of mass is sometimes called it's defined as a point where the weight of an object is considered to act so we always assume that the weight acts through the center of the object even though the weight actually pulls the entire object down from All Parts but we simply assume it's acting through the center but if an object is not uniform it doesn't have a constant thickness or something it's non-uniform the weight will act closer to the heavier side of the egg of the object though it's going to act on the heavier side of the object closer to the heavier side now there's no need to get the exact location just a rough location is fine yeah before we talk about stability let's just do a quick review of how does an object fall in terms of forces how does an object fall here's the center of mass here's the weight when an object is tilted just a bit in the center of mass is here the edge of the object acts like a pivot so this creates an anti-clockwise moment so it goes back so if you tilt an object a very small distance it goes back very soon it goes back if you tilt it a lot however when will it fall when the force goes over the edge of the object which creates a clockwise moment in this particular scenario causing it to fall over an object is more stable as in it's harder to make it fall over by making the center of mass lower so the heavier the base of the object is the more stable it is that's great and making the object wider because if the object is wider and lower it's harder to make it fall a little hard to make it flip over and fall so it's more stable last but not least buff let's talk about energy energy is a scalar quantity and it's something we need to use every single day all the time right now I'm expending huge amounts of energy just talking and explaining things and I'm using a lot of electricity to make my monitors work and my microphone work and everything else and you know what if if I was feeling hot I would turn on my air conditioner which which would consume even more energy and after I'm done I'll be hungry so I'm going to need to eat because I need to recover my energy so energy is something you need in order to do a lot of things but energy has many different types like kinetic energy which is the energy of speed the faster you're moving the more kinetic energy gravitational energy which is the energy of height or position higher an object is the more gravitational potential energy it has it's not doing anything with it it's just stored because the because of how high it's going chemical energy which is energy stored in food in fuel stuff that you burn and batteries that also works elastic energy which is the energy stored in anything that is stretched like a spring or a bowl you know a bowl when you pull on the bow string and it bends anything that you bend or compress or stretch that's elastic or string like or a ball that you squish as long as it's deformed that's called strain internal energy or heat obviously when you heat something nuclear energy which is stored inside the nucleus of an atom this is often released through one of two reactions nuclear fission or nuclear fusion and electrical energy or electric potential energy right but how do you transfer energy like how do you move energy from one place to another either way you transfer it using waves so light waves sound waves heat or infrared waves all electromagnetic waves essentially so think ultraviolet and everything else all of these are just methods of transferring energy a cell light sound in heat are primarily things like Heating it's not just wave so you could talk about heating through conduction or convection we will mention those you need to doing work which is just applying a force on an object that's a method of transferring energy and the electric currents like you can transfer energy using electricity this is why I often say physics is mostly a study of matter and energy in relation to in lesson time obviously just matter and energy there are two equations that you need to calculate and this is extended only why do they not show up when I was writing extended Artemis was thinking hey did I accidentally add an a here so it's extended such a cringe I'm sorry sometimes I got these cringe jokes and I can't stop them my brain works in mysterious ways so just tell me I'm funny self-esteem and stuff anyway calculating kinetic energy how do we calculate this now you calculate kinetic energy using this equation half times n times VA squared half times mass times velocity squared so obviously the faster an object is they the faster an object is the more kinetic energy it has right gravitational the potential energy is calculated using MGH so Mass times 9.8 or 10 in the older Market schemes times height so the greater the height of an object the greater the gravitational potential energy of the object also the greater the mass of the object the more gpe it has right but remember uh core students year nines don't really calculate kinetic energy in GP that's why we're saying it's extended next energy cannot be created or destroyed it's only changed from one form to another very important law I'll just do a quick one quick example if you have a light bulb you have a light bulb what type of energy does it take in and what type of energy does it give out it takes in electrical energy and it gives out what light and Heat if I give in a hundred joules of electrical energy the total amount of energy given out also has to be a hundred also has to be a hundred so if I tell you hey you're giving out 80 joules of light then you're also giving out 20 joules of heat the total still has to be a hundred sometimes we represent this using what we call a send key diagram it's nothing special you've seen this several times in questions before which is like this basically we have a hundred joules of electricity going in which is then split into 80 joules of light and 20 joules of heat all of this like this diagram just shows you how it's split the smaller or thinner the arrow the less energy is split and the thicker the arrow the more energy split so if this is a hundred this is about 80 this is about 20. it doesn't have to be to scale or anything so if you take a look at this diagram you should be easily able to tell what the energy transformations are going on this is an example for the extended students again because we we're the ones who calculate gravitational potential energy and kinetic energy uh the mass of the cyclist of a cyclist is 90 kilograms this girl and her bike have a mass of 90 kilograms she writes down without using brakes or pedaling so it's just pure energy what's your gravitational potential energy at the top so yeah gpe is MGH so that's 90 times 9.8 times 10. 90 times 9.8 times 10 which gives me 8 820 joules then what's your speed this is a very common question so keep in mind the gravitational tension energy at the top changes to kinetic energy at the bottom always assuming no energy losses this is why I assume no friction or resistance so gravitational tension energy has changed to kinetic energy so what's kinetic energy half m v squared what does he want the speed don't let the word maximum confuse you of water don't let this confuse you maximum is just what's the final speed so let's substitute kinetic energy is 8820 because it's been changed from gravitational to kinetic half times M which is 90 times V squared rearrange this V squared is going to be equal to 8820 divided by half of 90 should be 45 and then we square root our answer to get V so square root 8820 divided by half of 90. this gives me a speed of 14 meters per second we have three final equations that you need to memorize work which is when you apply a force on an object and it moves a certain distance you've given it energy work is calculated using force times distance or energies for science distance I know it looks like the equation for moments but the difference is is that the distance is in the same direction as the force it's not perpendicular same direction so if I'm pushing an object forward the distance you take is forward by lifting an object up the distance you take is up power power is how fast your transferring energy It's Just Energy over time or work over time this is a very common equation because we use the same equation in unit 2 and thermal physics when we calculate heat to energy and I ask you hey how fast am I transferring the energy well here's the power and time what's the energy we use that a lot and in electricity so memorize this very important if I want to calculate energy and I given you power and time it's just Power Times time and finally remember when we was talking about how this light bulb takes in 100 joules of electricity gives me 80 joules of light and 20 joules of heat we say that this light bulb is 80 efficient what does that mean this means that it's successfully converts eighty percent of the energy into useful energy it's successfully converts 80 percent of the energy to useful energy so how what do I mean efficiency is the useful output so KT joules that's that's the useful stuff the heat is considered wasted energy I don't want heat I just want light so 80 joules divide by 100 joules times a hundred so it's 80 so 80 is useful this means we have wasted twenty percent so quick example uh a crate is pushed 12 meters that's the distance across horizontal floor against the 13 Newton that's a force force in six seconds here's time against or with I don't care calculate work I know the equation work is force times distance so that's 30 times 12 because that's force and distance so 13. times 12 this gives me 360. 360. juice calculate the power developed in pushing the Box so power is energy or work over time so that's 360. divide what's the time again are six seconds six so 360 over six this gives me 60 watts the unit of measurement of energy is joules the energy measurement of energy is of power sorry is Watts and I'm sure you've all seen the Harry Potter meme if you're a putter head there's a Euro unit of power Harry and Harry responds I'm a what I love it I love it I'm not going to apologize for that green shock I love it anyway before I move on to power stations there's a question is it possible for him to ask me to calculate inefficiency no because inefficiency isn't actually a term but he could ask it directly you could say how much or what percentage of the energy was wasted like he has to stated that way but you can't just say what's inefficiency but yeah but he can't ask you how much is wasted so fatality what do you do in this case you divide that useless wasted energy divided by the two times 100. is there any other question here without asking when will we be done right after power station so in about in a few minutes power stations are large facilities that we used to generate electrical energy because we live off of electricity like everything in our lives depends on electricity so we need different methods of generating electricity we different sources there are renewable sources they are sources that return when they're used up like solar and wind and hydroelectric and waves in geothermal all of these are renewable sources of energy and non-renewable sources of energy like coal oil and gas these are fossil fuels and nuclear energy uranium that we use in nuclear fission nuclear efficient is a process where you take a nucleus and you break it into smaller pieces smaller nuclei to release energy which converts nuclear energy into heat and light changes nuclear energy into heat and air and Light in general all of these have both advantages and disadvantages obviously renewable sources advantages are one they're renewable two almost all of them cause low pollution whatsoever it's a very big advantage this Advantage is that they're not very reliable like you cannot generate electricity at night using a solar panel for example it's a big disadvantage okay none real and they don't generate as much power as non-renewable by the way non-renewable sources have very strong advantages they produce large amounts of energy and they are reliable and they work 24 7. day night raining or it's not raining snowing or it's not snowing as long as I'm feeding it with fuel it's generating electricity disadvantage is that they almost always cause a ton of pollution depending on the type so if it's air pollution you know manipulate the water you've got a lot of waste that you throw into the ground you've got nuclear waste that causes you know cancer and ionization it's very dangerous so all of these are a disadvantages and obviously they're non-renewable they will eventually end they do not come back when they're used up although of the three also Fuels Gas is the cleanest it causes the least amount of pollution and recently a lot of scientists have been working very hard on nuclear fusion which is a very clean source of nuclear energy we use hydrogen and we fuse it together to form helium and that also releases energy it's a very difficult process but it's very clean but that's another story let's quickly go over the power stations and how they roughly work you have a boiler in the chemical Power Station you burn your fuel which converts chemical to heat energy the water turns to steam the steam hits what we call a turbine which is just a big fan the turbine spins a generator remember the one with the coil and it's between the poles of a magnet and it cuts the field to generate electricity same thing so it converts the kinetic energy of the turbine as it's spinning into electrical energy the water then condenses we send it back to the boiler rinse and repeat this works for oil and gas and coal and sometimes biofuels by the way like when we have waste fuel from you know Farms you know stuff that you can burn we just burn that and we can use it to generate electricity nuclear power stations work almost the same way with the exception is that first we have a nuclear reactor where nuclear fission occurs this produces Heat and the heat boils water the water turns to steam steam hits a turbine the turbine spins and the generator spins which generates electricity so nuclear to heat and the reactor kinetic to electrical in the a turbine engine hydroelectric power stations we build a dam we block off the flow of water just like a beaver does but better when the water level starts to rise because we've blocked the water it now stores gravitational potential energy because it's higher than the rest of the river when the water falls and falls down whether it's from the top or from the bottom it doesn't matter we convert the gravitational to kinetic energy which spins a turbine and the turbine turns a generator and the generator produces electricity geothermal is a very important one it's just like the coal and nuclear power stations in terms of how they function but we have the boiler underwater and sometimes you don't put the boiler itself we just have pipes underwater we drop cold water down into the hot rocks that are underground so we go to places that are naturally volcanic and they have very hot rocks underground not not love obviously but just hot enough to dump a lot of cold water down there it boils turns to steam the steam goes up and turns a turbine and a generator it's the same process with the exception is that it's renewable geothermal energy is a renewable the last three are very simple wind turbines just convert kinetic energy of the wind to Electric you know wind hits this it turns we generate electricity done wave turbines are the same thing but we use flowing water to turn the turbines or make them vibrate up and down which convert kinetic to electrical energy right away no other steps solar is even simpler you've got light from the sun that hits these panels and they immediately convert it to electrical energy you'll notice that solar panels are the only method of generating electricity with no turbine and no generator meaning there are no moving Parts it's purely a plate which produces electricity using light right away and finally hello [Music] all right it's not okay a very common question is this is the sun the source of all of these types of energies well yes and no the sun is the source of coal and oil and gas and hydroelectric and wind energy and solar energy the sun is not the source Sport and this is what you need to memorize that of tidal energy which is high tide in low tide it's just like hydroelectric between multi of geothermal and nuclear energy why because nuclear energy uses uranium as fuel which is just a metal that we dig from the ground does not come from the Sun geothermal it's just heat from the core of the earth that has heated certain parts of our crust so does not rely on the sun tidal which is high tide and low tide the change in Tides is due to the Moon so it's unreliant on the Sun all of these come from the Sun colon oil came from living organisms that used to live millions of years ago they were alive thanks to the sun producing plants and the animals would eat those plants and so on hydroelectric energy comes from the rain cycle water heats though I'm sorry water in the ocean is heated by the Sun forming clouds the clouds rain you get the idea wind comes from the sun because the sun heats up our atmosphere the differences in atmospheric temperature from one region of the Earth to the other causes it to move and do I need to talk about solar energy that's literally directly from the Sun I didn't think so thank you very much we'll stop here but today that's unit one I'll see you guys for the next revision sessions