so we are gonna do some physics review here I'm gonna be going fast through some of this stuff so anytime you need to pause take a better look at what's on each of the slides please do but if I actually go over everything here it will take forever so I'm gonna try to make this as short a video as possible but please review the notes afterwards as well okay so let's first just talk about what we started with in the physics unit and that's all about motion okay so first thing that we went over was uniform motion so that's just something that's traveling at a constant rate in a straight line right the same distance over time and when you look at the distance time graph it's a nice straight line like that and then we looked at average speed okay and that is when we have this uniform motion so then we have a nice constant speed so that is just your distance traveled divided by the time that has elapsed okay another way we can calculate average speed is by figuring out the slope of a line on a displacement time graph make sure it is a displacement time graph right so this could be x1 y1 and this could be x2 y2 right and then you can find the slope from there so let's go over one example we have a huge ocean wave or tsunami travels a distance of 4 times 10 to the 6 meters 33 point six times 10 to the 4 seconds okay so calculate the speed of the tsunami summer speed V is just distance divided by time elapsed and we're given both of these what we don't need to do any conversion or anything like that so we have four point zero times 10 to the 6 meters divided by three point six times ten to the four seconds hopefully you know how to put scientific notation and on your calculator so that gets us 111 meter per second now remember another thing you had to do in physics is pay attention to the significant digits here we have two and here we have to sort answer needs to also have two so I'm gonna put that as one point one times ten to the two meters per second okay if you need any more help with significant digits things like that how to put things into assignment scientific notation I'll go back and look at those lessons again all right and then let's a look at speed time graphs so we know uniform motion on a speed time graph is something like this where it's just a straight horizontal line any time you have a slanted line that means you have acceleration okay so acceleration is happening here this is nice constant speed okay right here where there's where there's a horizontal line if I want to know the distance that this is traveled when we have a speed versus time graph I can find the area here underneath all here and that area will tell me the distance that's been traveled then there's scalar versus vector quantity so when were scalar is how much but no direction and then a vector is how much and in the direction so scalar is what we just say is magnitude vector is magnitude and direction okay so pause the video go over these eight things see if you can remember which is scalar and which is vector okay you paused you promised acceleration is a vector we care about Direction their displacement also a vector distance is a scalar we don't care about this direction their energy that's when people forget that as a scalar force is a vector speed is a scalar and time is a scalar because we only go one direction with time and velocity is a vector okay so let's talk a little bit more about velocity so like I said before if you have a and time graph or displacement time graph then your slope is going to be the velocity right so you choose your two points on the line and you can find slope from there okay or if you don't have that you can just do displacement over time just remember it has to be displacement not distance and displacement is very different okay another example an airplane flying at a velocity of 900 kilometers per hour west travels 400 kilometers west so remember West means we're gonna be going or making it negative okay if you remember we're gonna look at our orientation here's north your so here's East here's west north and east are your positives south and western your negatives okay so I have a velocity of negative 900 kilometers per hour and a displacement of negative 400 kilometers so I'm looking for time when I look at my velocity equals displacement over time equation I need to solve for time so what I'm gonna do I'm gonna first get time out of the denominator I'm going to multiply both sides by T okay that cancels that out we get T times V is equal to the displacement also not what we want so then we are gonna divide this side by the velocity this side by the velocity because therefore it cancels out and we are left with an equation that we can use which is T is equal to displacement over velocity okay displacement again was negative 400 kilometers velocity was negative 900 kilometers okay in our answer we want three significant digits a negative divided by a negative is a positive which totally works out because time shouldn't have a negative on it okay so what I get there is 0.4 continuing so to make that three significant digits I need zero point four four four no need to round up okay oh that's km/h those can't slope we are left with hours so point four four four hours and it doesn't say what we needed it in so I'm gonna leave it at that if we needed minutes we times that by sixty if we needed seconds we multiplied by 60 again acceleration is just the change in velocity during a specific time interval so that remember that on a position time graph like we have here if you see a position time graph curving like this that means there's no uniform motion okay it has to be a straight line if it's a uniform motion it's you also know it's accelerated in motion on a velocity time graph if it's not flat if it's slanted that means it's accelerating okay and remember acceleration is your change in velocity divided by time so if I wanted to do another example of that we have a racing car accelerating from rest to a speed of fifty five point six meters per second east so that is a positive direction in six seconds what is the acceleration of the car it's remember acceleration being change in velocity that means final velocity minus initial velocity divided by time okay so here our final velocity is fifty five point six meters per second because that's what it's speeding up to its initial velocity was zero meters per second because it accelerates from rest okay divide that by the time which is six point zero zero seconds and we get and also by the way we're looking for something with three significant digits and that is nine point two it's nine point two six continuing so that looks like nine point two six six six six six six six keeps going so if I want to round that up to three significant that'd be nine point two seven and we got m/s^2 as our units there okay so there we go there's acceleration the next thing we talked about in physics was work and that's remember when a force moves an object through a distance it does work so it's just Force Times distance do you guys remember what is required for work to be done though the force in the distance have to be in same the same direction okay so if I'm lifting something or sorry if I'm holding something up I'm applying a force upwards but if then it's moving sideways then those are not in the same direction okay so now we're gonna go over energy and how work is related to energy so remember sometimes times types of energy ones that we didn't necessarily go over nuclear energy that's energy stored in a nucleus solar energy obviously energy stored in the Sun chemical energy the energy that's given off through chemical reactions electrical energy which is basically just a bunch of electrons moving around and then ones we did go over potential energy and kinetic energy remember potential energy is energy that's stored we did define stuff like elastic potential and chemical potential energy but that one we have a formula for is gravitational potential energy and remember that's EP is equal to MGH where M is mass in kilograms G's your acceleration due to gravity 9.81 m/s^2 and H is your height in meters I remember this is all on your data sheet you don't have to memorize the formula don't have to memorize 9.81 let's do an example of potential energy we have a fifty five kilogram driver standing on a diving standing drop nut-driver divert Wow sitting on a diving platform gravitational potential energy of five point four times ten to the three jewels I want to note that vertical height so I know EP is equal to MGH and here I'm actually looking for H so I need to isolate it so in order to do that I got to divide both sides by mg because that cancels it out there and we get that height is equal to potential energy divided by M times G okay so again my potential energy was five point four zero times ten to the three jewels I'm gonna divide that by mass just fifty five point zero kilograms times G which is always the same nine point eight one per second squared please you guys please please please put that denominator in bracket so when you're typing this into your calculator you're doing five point four times ten to the three then you're dividing it and then you put a bracket and put fifty five times nine point eight one and end the bracket there okay and that gets you well we need three significant digits but isn't this nice it's just ten point zero and that is meters it's all we're looking for so there we go there is the height they Dovre okay then we went over kinetic energy which is just the energy that something has when it's moving okay still in joules and your formula is right here which again is on your data sheet okay M is mass visible acetate masses in kilograms and velocity has to be in meters per second so you if you ever get kilometers per hour you have to convert it to meters per second okay let's do an example of that we have a small toy car moving horizontally at uniform speed 2.2 meters per second and it has a kinetic energy of 18 joules so now we needs to calculate the mass so again here's our netic energy formula and here I need to isolate the mass right there so how do I do that first I multiply both sides by 2 because it's the opposite of multiplying by 1/2 technically you could be dividing by 1/2 but it's same thing guys so I get 2 EK is equal to M V squared and looking for it m to be all by itself so I need to divide by V squared a lot of people think I need to do something with that squared that squared only applies to the V not to the M so if you divide by V squared you are done you're good ok so here we get that mass is equal to 2 times the kinetic energy divided by the velocity squared all we got to do so two times the kinetic energy which is 18 joules divided by 2.2 meters per second squared and keep in mind the answer needs to be two significant digits because that's what we get in the question and we get 7.4 that would be kilograms okay and the calculator get seven point four three eight blah blah blah blah blah but again I only need two significant digits so I just look at the seven point four after the four is a three so it does not need to be rounded up so there we go there is the math for that question and then we won over mechanical energy you guys remember mechanical energy so that's basically the sum of kinetic energy and potential energy okay that's all mechanical energy is just take the kinetic energy at a point and the potential energy and add them together okay so remember usually we went over situations where mechanical energy was constant okay so that means mechanical energy here is the same as mechanical down here but it's just being added in different ways right so at the top here it has lots of potential energy but really low kinetic energy so maybe that potential energy is 10 joules and the kinetic energy is zero joules right but maybe down here the potential energy is zero joules and the kinetic energy is now 10 joules right so it still ends up being 10 but we just get there in a different way so that's what we did for conservation of energy saying the potential energy at the top is equal to the kinetic energy at the bottom okay so here we have a 1.5 kilogram rock so there that's a mass okay dropped over the edge of a cliff 30 meters above the surface so that's the height we want to know what's the speed of the Rock just pour it strikes the surface of the lake so it looks like we have enough information to find the potential energy okay and then we need to find the kinetic energy but we know that potential energy at the top here is equal to the kinetic energy at the bottom of this things of this rocks fall okay so there's two ways to do this just find potential energy by going MGH and that's equal to your kinetic energy okay but I want to just use this thing because a lot of you guys forgot that you could do this and it's actually a bit of a shortcut because we know since potential energy at the top which is MGH it's equal to kinetic energy at the bottom that's equal to one-half MV squared okay and then there from here we can just solve for the velocity and because we have em on both sides guess what happens when I try to divide both sides by M they both cancel out so in these questions you don't actually even need mass okay so what I actually end up getting is that gh is equal to one-half the squared okay so if I want to rearrange that for velocity multiply both sides by two okay - gh is equal to V squared and then to get V we just square root both sides okay so that means velocity is equal to the square root of 2gh okay if you don't like this method you do not have to use it whatsoever but it actually is a bit of a shortcut and I don't even need to worry about mass so if you get good at using this kind of situation or this technique and no one to use it right know that when we're talking about something that's going from this highest height to its lowest height that's when you can use this method because then here I only need the height I do not need the mass whatsoever it gives it to us okay okay and so that gets me at twenty four point two six but how many significant digits do I need I have three there and three there so I need three which gives me twenty four point three meters per second and there we go that's my velocity okay and finally we went over things like systems and laws of thermodynamics and stuff like that okay so remember systems you can have open closed or isolated open exchanges everything closed can can't exchange matter but it can't connect can't exchange energy and an isolated system you can't cheat exchanged anything with the surroundings the first law of thermodynamics was you can't create or destroy energy you can only transfer it from one form to the other and the conservation of energy is the total energy including heat in the system and its surroundings remains constant okay so that those are pretty much saying the same thing then your second law of thermodynamics as heat always goes from hot to cold always it will flow naturally from hot to cold never naturally from cold to hot okay so remember there's some energy when we're trying to get something to do something there's useful energy and there's energy that comes out anyways that's not as useful right so when you light a lightbulb the usable energy is the light the not useful energy sometimes is the heat that always comes off with a light bulb okay so the initial source is called the energy input so with a light bulb that would be your electrical energy the desired energy is called the output okay so whatever the output is is just the work that the machine it's supposed to do so if we're talking about a light bulb it's in the name you need light right so anything that's not giving off light is not useful energy output okay so we used that kind of concept to calculate efficiency of different systems okay so remember that it's just useful work output divided work input and then we just change that into a percentage by multiplying it by a hundred okay if you're ever worried about that remember you can't have over 100 percent efficiency so if you get over 100 percent something's wrong you probably need to switch your output in your input okay you probably have the wrong numbers for that so output should always be smaller than input we've got a bunch of different energy sources so just know that energy can come from all these different things right so that wind energy water biomass fossil fuels and then non solar is from geothermal and tidal okay and some of those are renewable like solar wind water only if the water is recycled right if you're using the same water over and over then it's not knowable we're sorry renewable do you thermal so that's basically just using heat that comes from the core of our title that's basically the water and the oceans and the tides and stuff like that and biomass which is plants and things like that that of course we're planting again and again and again and again not a newa belitz stuff like nuclear because we only have so much nuclear fuel source and fossil fuel okay so that is the physics unit in a very small nutshell okay so good luck with studying for that