Transcript for:
Forces and Motion Overview

hello everyone welcome back to this channel so in this video we are going to look into IGCSE physics chapter 3 forces and motion and these are a list of topics that we will explore first we'll understand what are the different types of force that is um that we experience on a day-to-day basis and followed by a specific type of force called CAP gravity and how the gravity on different planets will be different then the third subtopic will go through is how the term Force math and acceleration in which we touch on chapter two they all interrelate with each other last but not least we'll finish up with momentum and impulse which describe how to quantify the impact of a force and what are the different quantities scalar vectors quantities that we have so without further Ado let's dive deep into the first subtractor which is on Force so forces are basically just pushes and posts that affects object as they move and the unit 2 quantify forces are called Newton which is named after the famous physicist Sir Alex Sir Isaac Newton and because of his contribution and the mechanic physics so so here are the different types of force first we have weight so the weight here is not how heavy you are in fact that's mess but um in day-to-day conversation we use weight but weight in physics is basically just the gravitational force exerted by the Earth um on all the objects on Earth they are proof of gravity and then we also have contact force which is so for instance I'm holding this pen now and gravity is acting on it but then the reason it doesn't fall down is because it has contact force between this pen and also my finger all right it stops us from falling through the floor or we can see how it stops this pencil from falling down and the types of force we have frictions the first act when two surfaces rub each other and air resistance so it's very much like friction but it happens in the error and also water and water is called drag so brackets for liquid and air resistant is specifically for air so the last type of force is up trust so when you're assuming you will feel an upward push of the liquid that push it up even though you don't indent you don't include any force in it so here are the five different types of force and overall all types of force when it is unbalanced and then this means either we have a stronger downward force or stronger Force to the right or left will do two things mainly the first thing is that it will change cause the object to change speed for instance in the car example here if you want to increase the speed of the car you want to accelerated you need the engine we need to exit some additional Force to counter the friction that's on the road and besides changing speed an unbalanced force can also change the direction for instance the next example an indirect Force unbalanced force will change the direction of the ball and here's the um the first law that we'll learn called Newton first law it says that a body will remain at rest or move at a constant speed in a straight line unless acted upon by a resultant Force which is related to what we just talked about here if there is no Force if the force are balanced an object will always be for instance in the car it will be in constant speed whereas um same goes to the sport if there's no external force acting on it no friction it will just keep on moving in the same direction forever that's when Newton's first law comes in because when there's no resultant Force it won't change direction it will certainly change in its speed all right so so now now let's understand what what does Newton say here when he said result in force so in this example here two person is pushing this box here and each person let's assume that they are exerting a force of 200 Newton so resultant force is the sum of multiple forces so in our case here since the 200 Newton is accelerated in the same direction to the right we can say that there is a resultant force of 400 Newton towards the right hand side it's like one person exerting 400 Newton whereas here we have a work example here which shows what if the two forces are in an opposite direction so in here we have the engine exerting 600 Newton to cause the car to move whereas 400 Newton towards the left is the friction so in order to calculate the resultant Force we have to turn this Force you contain either one but I'll return this one into negative as a result we have so 600 Newton minus 400 is minus here because this is in the opposite direction and therefore the resultant force is 200 Newton the keyword is to the right hand side and understanding what resultant force is important in a lot of the applications and a lot of the question will be solving in a while so in this case we have another case whereas the engine truss is 600 exit 600 Newton force and the friction is also 600 Newton and if you remember Newton first law if there's no reason to enforce in this case 600 minus 600 will have exactly zero Newton meaning there's no result in force and it means that it doesn't necessarily mean that this car will stop it's just that if it is moving at its rate of 20 meter per second it will remain at that speed like Newton first law if there's no external Force if the object is suppressed it will remain at rest but if the object is moving remain at the same speed so it's either remaining at rest or you move at the constant speed like before all right so that's all about Force we're definitely look into how we can apply the different types of force and question later but before that now we'll dive deep into a specific type of force called gravitational force which is false accented by the Earth on every object in the verb and under this chapter we'll also dive into the further subtopic like what is gravity and also what happens during Free Falling and like a skydiver and what are the force involved when an object is moving in a circle so make sure you watch till the end so here we have a falling wall snapshots that basically explain why this board as time passes here as time passes if move further and further and the reason this is so is because the ball is moving faster at each second is accelerating as we learned in chapter two and what causes it to accelerate right so here we have an answer here I will highlight it using the yellow color line is the force of gravity that is pulling the ball down so gravity is basically that the Earth is exerting a force like this imagine there's a ham here I'm not very good at drawing but imagine there's a chance here that exits Force to pull the ball down and that's gravitational force and the amount of force used exerted on the object is what we call weight so for instance um later on if I say that I have a full weight of 500 Newton it means that there's 500 Newton of force exerted by the gravity on me as a person all right so the on Earth here we have a fact is that for every kilogram of object 9.8 Newton will be exerted on the object so I have an example here so two balls one is five kilogram the other one is one kilogram and they will all fall down because gravity is pushing them and for one kilogram of matter from the example we learned just now is that 9.8 Newton a forces pulling it down whereas in this 5kg example here we will have 9.8 multiplied by 5. which will be 49 into pulling the board down all right so the question here is that which wall would touch the ground first and intuitively you would dot that one of the five kilogram ball will touch the ground for because it's more Force but is this not the case especially when you learn about Newton's Second Law later um the answer to this question is basically both walls will touch the ground at the same time because um the gravity is pulling the ball together they're pulling each kilogram so I split this ball into five parts so imagine that gravity is pulling all of them down at the same time so therefore regardless of the weight of the ball both balls will touch the ground at the same time so that's just one thing you need to take note of all right so we know that just somebody said that gravity will cause something to fall down and then it also cause the objective accelerate and this accelerate is called the acceleration of free fall and the other name for this is called the acceleration due to gravity all right so now that's we have been talking about weight for a long time now so let's learn how to calculate an object's weight and do note that if today I said I'm 60 kilogram I'm not saying that this is my weight in fact that's actually my mess usually in kilogram and in order to calculate Weight there's a formula here in which you multiply the mass kg by the acceleration to 3 4 and the acceleration on Free Fall is basically usually 9.8 on Earth and it's the other way around um it's another value in another planet so there's so here we have a slide on the difference between Meson weight so mass is basically how much matter an object is composed so the mass of this pen is going to be the same on Earth or on moon it's going to be the same because the method here is constant whereas the weight of something is the gravitational force that act on this object and the weight of this pen here is going to be different on Earth as compared to it is on mood so that's that's on one term so we have two term weight Mass gravity acceleration of three four and that's the third term we have a third term here called gravitational field strength it's basically a term used to describe how much gravitational force in Newton that acts on one mass of kilogram in a certain planet so we have two planets here planet Earth and also planet um Moon actually examples so on Earth here um Earth exert 9.8 Newton per kilogram of object all right so meaning if this pen is one kilogram there will be 9.8 Newton pulling it down whereas if this pan is on the moon itself the gravitational field strength is lower um here it's only 1.6 meaning that if this turn is on the moon only and it's weight 1 kg only 1.6 Newton of force is exerted on it to pull it down okay so let's look into some work example to help you grab the concept um we have a back of sugar that has a mass of one kilogram so its weight on Earth is 9.8 Newton because W equal to mg is the formula so if my sugar is one kilogram and the gravitational fuel strain of Earth is 9.8 so it's going to plot that in I have 1 times 9.8 which is 9.8 Newton that's what they are saying here they're asking what is the weight of the sugar on moon and assuming that the acceleration due to gravity and moon is 1.6 so I'm going to use the blue equal to mg again so because the mass of the sugar is going to be one well nothing will change here therefore I'll use one as my mass and the group G here gravitational field strength equivalent to a gravitational acceleration it's 1.6 so I'm going to do 1 times 1.6 so the ultimate answer will be 1.6 Newton on the back of sugar and so that's the answer and question B the weight of the sugar on the planet Jupiter is 23 Newton so now again using the same formula W is equal to 23. and the mass of the sugar will still be one regardless of you know where it is so my Mass is going to be one and a question is what is the gravitational field strength of the planet so to find G I just use 23 divided by one which is 23 Newton or you can say um the the gravity acceleration of Free Fall is 23 meter per second Square so which is a little bit higher than on Earth so that's it gravitational field strength 23 meter per second Square so here's the positive question that asks how is the weight of an object defined and before learning this chapter you might say that the answer is B meaning just how heavy it is but after this chapter you should know that the weight is basically the gravitational force that pulling the object down so the answer answer should be donkey the force of gravity acting on an object yes D is the answer so second question and that's pronounced by a five kilogram tint on quality Street chocolate so he bought a chocolate on Earth and then very funny he bought the same chocolate to the moon now what is the mass of the team so do note that here they're asking for the mess not the weight and the mass of an object will not change regardless of where it is placed so the mass of the tin on the moon will be exactly 5 Newton but if let's say the question asks for weight instead because the gravitational field strength on the moon is lower so the chocolate there will have a lower rate but in this case as mass looks gonna be five kilograms all right so let's look into the sub subtopic of this subtopic following through the air so all objects here which we mentioned this now they fall with the same acceleration on Earth but today a watermelon will fall faster than a feather and it's not because the gravitational acceleration is different but because of the air resistance overcome by this feather is greater all right so let's look at um this skydiving example tell us understand how and people are able to do this with their parachute so just to know that Essence driver as the skydiver is falling down its weight does not change and at first the weight is going to be the weight which is the gravitational force on peop on a person it's going to be greater than the average distance and hence we have a resultant Force to be more precise is a resultant downward Force and when there is a resultant Force an object will accelerate according to Newton first law and this is why the speed of this parachute increases Point number three because when the speed increases the more the air collide with the parachuter faster and as a result air resistance increases until one point the air resistance is equal to the weight of the parachute and this is when the parachute reaches a form called which is a speed called terminal velocity so remember now there is no resultant force it doesn't mean that the parasitum will stop but it's just that it will maintain at its highest speed it's just that the speed will not be increased anymore and this exact speed is what we call terminal velocity is the maximum velocity attainable by an object as it falls through all right and now the the parachute is falling down at very quickly and in order to stop he gets he just cannot just um move like that otherwise he'll die therefore he needs something called like a parachute so that's what this parachute does is that the movement is open it's gonna greatly increase the air resistance all right so there will be the r resistance will be much higher than the weight of the parachute and as a result the force again become unbalanced there's a force upward which causes the parachuter to decrease in speed and now the parachute will reach a new terminal velocity around 10 meter per second in which he can safely land so that's the five to six points um that the parachute encounter so here we have also the speed time graph of the parachuter um that's something we learned in chapter two if you need to learn more about that you can watch my chapter 2 video so initially the parachuter speed increases drastically because there's a resultant downward Force the weight is a lot greater than the air resistance and as the speed of the parasitor increases the air resistance also increase until a point when the weight and also the errors is then equal each other this is when the parachute reaches terminal velocity and in order to slow down parachute is released here and then now the parachute will speed will decrease to a point where he can safely land and by the way if you're watching this and you want to get the slides here to revise or your teacher you want to use it to teach in your classroom please feel free to visit my website down in the comment section and um thank you first for always supporting and that's it let's move on another positive question skydiver is falling at terminal velocity he has not yet opened his parachute and he dance open his parachute what is the direction of both the velocity and also his acceleration and the direction means whether he will go up go down or up and for velocity obviously since he or she will still be moving downwards the velocity is going to be downwards but as for the acceleration if you remember when after the skydiver opened his parachute the r resistance now is higher than weight and therefore he or she will not um be going in the same speed anymore he will he or she will go slowly so the acceleration is still going downwards there's a force of acceleration going upward to cause the skydiver to slow down and that's why the direction of velocity is going to be downward and acceleration is going to be the other way around that slows the skydiver down and that's how we can answer it and the answer should be C correct so um here's the paper 4 question a vertical cube contain liquid a metabolous held at rest through this metabol and thrown in the diagram and the diameter is much greater than the diameter of the ball meaning it can just fall very easily the ball is released and they accelerate downward uniformly for a short period of time the ball reaches terminal velocity I just want you to see that how similar this question is to our Parish to our strata by example they're basically the same thing just without the parachute so when they say this carbon explain the motion of the ball until it is when it's released until reaches terminal velocity we can basically just talk about stuff that we just talked about in our skydiver example so first of all the weight we can talk about the weight how it is greater than the air resistance right and as the ball accelerates I'm just using short form to save your time but I will have knocking scheme in the back asset accelerate the speed increases and when the speed increases is going to be the air resistance will increase at the point when the downward force is equal to the air resistance meaning there's no resultant Force the sky the ball won't speed up anymore this is when it reaches terminal velocity but of course when we write on so we do have to write in sentences like this I've attached a marking scheme here which is basically just what I discussed and this is how you can get all one two three points all right let's move on to another example and here is the skydiver example so this skydiver is 4000 meter above the ground at time 30 issue opens her parachute and here we have a speed time graph so now we need to describe in terms of forces acting on the skydiver and her motion between leaving the balloon and opening her parachute so it's the same thing as the last question so we can just look at how the answers can require us so again the weight part is mentioned and there's air resistance and when the speed of the skydiver increases air resistance also increases and when air resistance increases there will be no more acceleration okay acceleration decrease and until a point where there's zero acceleration when the weight of the skydiver is equal to the air resistance so that's just a guide on how you can answer asset question I think that's the hardest part in igcsd physics is that sometimes we just don't know um how to answer the question to get all the points and hopefully this slide help you them so now here's another subtopic which is we should describe the force that is happening when an object is moving in a circle so let's read this when a car turns a corner it changes Direction any object moving along a circular path is changing direction as it goes so if I were to draw a circle here oops sorry for car okay let me draw better so I have a circle here and if my car is moving in a circular track like that it is what they're saying here is that it keeps changing it is keep changing direction so to change direction remember Newton's First Law Without resulting resultant Force an object will just stay on track that's why if an object wants to change direction of also if you require it which is what's being here so for instance if this airplane here wants to move around in circle while maintaining its speed you need to exert a force on the left wing or right wing in order to change direction and second example how moon is able to orbit the earth it's also due to force because there is an intangible cannot invisible false pool of Gravity by the Earth to move the moon in of it so so here's some facts about um going around in circle so if an object is moving in circle like that meaning the force that exerted um the force has to be towards the center in this example the force is from the Earth's gravity all right so the size of the resultant force that means what are the factors that affect these forces is that first is mass the heavier object the bigger the force is needed to keep it moving in circle and also the faster you want it to move the more Force you need that's pretty common sense whereas the third one is radius that means the smaller this radius of the circle the bigger the force that is needed to pull the object and circle so that's just three factors that in affects the force in a circle and here we have an example of how um the law of physics and work here it's called a war of death so basically all the drivers they could be driving motorcycle car they'll just move around this circle and I'll attach a video here to let you see what it is like but efforts it looks like magic but then now we know that because they are able to stay on track without falling down because they are tired here it's in contact with the wall with all this water that provides an upward force that helps them to stay in Balance okay the friction force and the weight force is spelled equal that's why they won't fall down in this example so that's just one application of how fossil systems are involved in a circling in a circle setting all right so let's look at some positive question the moon orbits the earth at a constant speed which of the arrow on diagram shows the direction of the resultant Force so for the moon to move in circle as mentioned the force directed at it must be towards the center so it's going to be D my answer is donkey all right so a um another question the diagram shows the model car traveling on a flat circular track the speed of car increases at Point p on the diagram and the car does not stay on track state in terms of force while the car does not stay on the track at Point P that's how we say that in order to move um in order for the car to move in circle uh the force of an Epub directed towards the center and the copy here no longer stay on track when it speed increases and one reason could be that you know the force is not strong enough to pull it in circle because its speed increases and because the faster is moved the more force is required so in this example one reason could be the force it's not strong enough to pull it in circle all right so that's the answer and for B on the diagram draw and label an arrow with the letter s to show the direction of motion so if this P copy here no longer stay in the circle um you can just write draw it like that this is where it will go all right it will leave here and then move to us um this trick all right so that's basically the answers so now we finish gravity and also how gravity is involve in terms of going around the circle and also parachuting and now let's proceed to how the following three quantities Force mass and acceleration they all relate to each other in fact it's a very famous law called the Newton Second Law all right I'll just write down here Newton's third Second Law describe the relationship between force mass and acceleration so there's an equation that describe how these terms relate with each other which is false equal to mass time acceleration all right so this law basically states that if an object is very heavy in order to accelerate it you're going to need more Force so for example let's look at the on this work example Workforce is needed to give a ball of mass 10 0.1 kilogram and acceleration of 500 meter per second Square all right so we have we need to find F and we know that the three terms can be related using the equation F equal to me and to Define force I can just plug in the mass number 0.1 acceleration 500 and to the equation and then if I plot the value into my calculator I get 50 and the unit for force is going to be Newton all right yeah so that's the answer so here I want to give you some intuition on how this law basically works so if if I would take Z the same force on let's say a mass above Mass one kilogram instead of 0.1 I increase the mass to one kilogram you see that now the acceleration is going to be a lot lower all right um it's going to be 50 meter per second Square so this law actually makes sense because imagine I have two objects one is heavier than each one the other and if the same force is applied on each item the lighter object is going to have a faster acceleration and then so that's what how this quantity is relayed together with each other all right so let's try to solve another example to help you solidify your learning so an Airbus aircraft has four jet engine each capable of providing 320k of newtonous trust and the masses this heavy what is the greatest acceleration so the trick Point here is that we are having four engine instead of one engine and according to the question they said that each engine is going to be able to provide 320 000 Newton so if you were to find acceleration again we can use the formula f equal to m a and what is the force here if the force here is going to be 220 000 multiplied by four because four engines is on the plane and we can just plug the mass into the equation identify acceleration I can simply use the force divided by the mass of the object so if I were to plug that into my calculator I'm going to get 2.28 meter per second Square so that's the acceleration that the Airbus can move so that's an example of how we can solve it all right 2.28 so let's look into another positive question here a bus driver along a flat Road its engine produces a forward driving force of 7000 Newton and track is also acting on the bus track is basically the ad resistance right the the bus has an acceleration of 1.2 meter per second square and a mass of 2500 what is the value of this t-shirt all right this is basically a tricky question first of all we need to find out what is the resultant force acting on this bus and how are we going to do that since acceleration and math is provided I'm gonna have I'm going to use the F equal to ma formula and I will do 2500 multiplied by 1.2 and if I were to plug that into my calculator I'm gonna get two thousand oh I'm gonna get 3000 Newton and that's the resultant force acting on the bus so knowing that the resultant force is 3000 I can use the resultant Force it's going to be equal to forward Force minus backward Force so my resultant force is three thousand and my forward truss show my diagram is 7000. so therefore I can calculate my drag so instead of backward I'll put d my drag using the formula 7000 minus three thousand so I have four thousand newton and the answer is going to be donkey so here's donkey and I'm including by the way if you're watching this for the first time um including passive questions so that you can apply whatever you learn in this video into questions and I believe this question will build your confidence to score in your enzyme all right so let's move on to the last two topics momentum and impulse so momentum is an interesting topic because a lot of students have told me what they don't still don't understand what it is so now I want you to think of momentum that is a measure of an object's ohms so this is a relatively informal way or you can say how um the resistance the object's resistant to changes in motion so for instance I have a train here and also motorcyclists here so if they both of them were to move towards this person obviously we're going to know we know that it's harder for the train to stop as compared to the cyclists so in other words I can say that this train has a higher resistance towards changing emotion which is stop so this bus I mean this train here is going to have a higher momentum than the cyclist and I believe this will explain better that momentum is actually calculated by using the mass of something multiplied by the velocity or you can also say momentum is the impact of a force how much impact the force is making and how if an object has high resistance that means it's harder to change its motion so that's the formula to calculate momentum here's another formula is to use momentum equal to mass times velocity so let's look into the work example a car of mass 600 kilogram is moving at 15 meter per second so that's the speed so to calculate momentum all we need to do is just to use the formula momentum P equal to MV is equal to mass which is 600 multiplied by velocity which is 15 and you plug that value into your calculator you get 9 000 and the formula and a unit for momentum since we know that mass is in kilogram and velocity is a meter per second we can just do kg meter per second you basically just multiply the two unit together that's about it 9000 meter per second all right so that's all about momentum Mass multiplied by velocity so let's move on to impulse so now we learn what is in the momentum um the impulse is basically the change in momentum momentum and some here we have a description the effect of false depends on two things how big the object is how big the forces and the time intervals it acts on so I have a boxer here just imagine that um you are the you have the boxer if you want a better damage you're going to touch the opponent's face for a longer period of time and that's basically creates a greater effect on the force and this is why um when we look into the impulse formula later you will see that impulse basically equal to force times time so you're exerting a force but the time that you exert the force is going to be affecting the effect of that Force so that's first formula for impulse you use Force multiply by time and the second formula is so another way you can Define impulses the change in momentum um how the momentum changes from one um one point of time to another so let's look into the first work example to better understand a car of mass 500 kilogram is moving at 50 meter per second so we have the mass we have the Velocity the driver accelerates gently so that a force of 30 Newton act on a curve for 10 seconds so 30 newton is acted on a car for 10 seconds we need to calculate the impulse of the force so again we can just use the formula here impulse is equal to force multiplied by time in which I will have 500 um 30 Newton since that's the force exerted multiplied by 10 which is seconds so the impulse is 300 Newton Second and that's it and this impulsing is you can also say that the momentum of the car changes by 300 because impulse is equivalent to the change of momentum and that's the answer 300 Newton Second so that's the unit for impulse again you don't have to memorize you just have to know that I'm multiplying Newton with seconds force times time so I just combine these two formula unit into one so calculate the momentum of the car after the accelerating Force has acted on it so from the previous example we know that in pulse is equal to 300. but we also know that impulse is equal to the change of momentum meaning the change of momentum here is 300 kg meter per second one so we we care about it the momentum of the car after the accelerating so before we calculate it the after effect we need to calculate what is the initial momentum of the car and we can calculate it using just the formula mass times velocity so let's go back the mass of the car is 500 kilogram and a velocity is 15. so we will have 7500 kg meter per second so that's the initial momentum of the car and because the change in momentum is 300 to calculate the final momentum I can simply use 7500 so Plus 300. and that would give me 7800 kg meter per second negative one inverse so that's basically the final momentum of the car and if we look at the result and that's the answer here right so that's about it um oh here's another question a force of 500 Newton acts on a rocket for 600 seconds causing the blockage velocity to increase again they want to calculate the impulse which is force times time 500 times 600 which will give me 30 000. Newton the unit of the force second the unit for the time let's move on so that's the answer and by how much does the Rocket's momentum increase we know that impulse is equal to the change of momentum therefore we can also say the change in momentum is 30 000 kg meter per second negative inverse or you can use this unit as well all right the impulse unit so um so far we have learned about momentum with Force so here is how we can relate momentum back to the force formula so from Newton's Second Law we know that the equation is f equal to m a and in Chapter 2 we also learned that the formula for acceleration to calculate a is V minus U over t and if we were to expand on this formula we'll get MV minus mu over t and hopefully now you can see that MV here V is the final velocity U is the velocity initial velocity but both are Velocity right and when you multiply mass times velocity it's actually the momentum and MV minus mu this part here is basically the change of momentum change of momentum so when you divide so here I introduce another formula which is how to really change your momentum back to force so when you divide change from momentum by time essentially you'll get the force of the object so in this case force is besides equaling to F equal to me so I could so equal to change in momentum divided by time all right um here's an application of how this lowest and work so we have a high jumper here how this cushion is able to reduce the impact is that it increases the contact time so when this diver fall on this map here it's gonna he's gonna stay down a little bit be in contact with the cushion a little longer as compared to when the cushion was not there it's going to be on the four and then hurt its back but because when we put a cushion there it's time increases therefore this guy here will probably not experience so much of an impact in fact he should be okay and that's because we increases the contact time and when you increase the contact time in the denominator if this value increases the amount of force experienced by the high jumper here is actually less okay so that's um let us look at one work example on how crash tests helps which is um how the airbag helps passenger to experience less false so initially this crash test dummy has a mass of 70 kg and it comes to a stop in 0.03 seconds in a crash whereas in the second test when the car is fitted with airbag this dummy takes five times longer to test which which means it takes instead of 0.03 seconds it takes 0.15 seconds and what force are acting on the dummy both tests and here I have the solution straight away Force because we know that we can calculate force using change in momentum divided by time we can see that in the no adab example the dummy experiences 35 000 Newton of force but then as we increase the contact time now the dummy experiences only 7 000 Newton of force and that's a way of how this formula that we um derive here comes into play why is it that when we increase an app when we Implement an airbag increases the contact time the driver is actually safer because the force experienced by him or her is less all right so that's all about um the change in momentum so here's another example on momentum hitting a ball with a tennis racket before the Heat and after they hit so what happened is that before the Collision the record is moving to the right and because the record has a mass right and when it's moving it also has velocity therefore it has momentum on it to the right hand side and after the Collision the racket is moving toward the right but more slowly than before this because all the momentum has been transferred to the ball so the ball now creates momentum it also has mass therefore it's free will also increase all right so let's look into um this principle called principle of the conservation of momentum meaning when the racket touches the ball so we know that record has momentum and when it touches the ball the momentum is basically transformed all the way to the ball and that's principle of conservation of momentum meaning the momentum of the initial object will not be lost in fact it will be transferred somewhere else okay and let's look into this example to better help you calculate how this momentum things work so here we have all the information the mass the velocity before it hit the ball the velocity after it hits the ball and the mass of the tennis ball velocity okay so now let's do the question is find the momentum of the racket before the collision and to find the momentum we use P equal to MV and the math of the racket is three and the initial velocity is 20. so the momentum is 60 kilogram meter per second so that's um the momentum of Racket before the Collision and we have our answer here and now we need to find after the Collision again use P equal to MV again the mass of the bracket is three the velocity is now become 18 and the final momentum is less than what we have previously we have 60 previously now it becomes 54. and according to the conservation of momentum we know that the loss momentum is actually being transferred to the ball all right so now we can find out what is the momentum of the ball after the Collision which is six kilogram meter per second because that's the momentum that the racket loss loses so the answer is 6 60 minus 354 equal to six kilogram meter per second and by using the momentum by having the momentum of the ball we can calculate its velocity again use the formula P equal to MV 6 and how heavy is the ball so the boy is 0.25 kilogram so we can use P equal to MV and we plot with 0.25 into the math to find the velocity we simply use 0 6 divided by 0.25 we will have 24 meter per second so that should be it the answers so I'm going a little bit faster so if you need to digest feel free to pause the video so let's look into the past year question and that's how we can learn better and every plane of mass 2.5 times 10 to the power 5 kilogram lands with a speed of 62 meter per second at Time Zero and the airplane then decelerate uniformly as it travels along the runway until it reaches 6 meter per second at t equal to 35. calculate the deceleration of the airplane so um here's the formula that we learned in Chapter 2 a equal to V minus U over T all right and the final velocity here is six an initial velocity is 62. I just basically just plug the value in I'm gonna have six divided by 62 6 minus 62 let's use the calculator divide by 35 I'm going to get Negative 1.6 meter per second Square so the answer is a negative because it's it's decelerating so when the question asks what is the deceleration basically you can convert it into 1.6 instead so um the next question calculate the resultant Force on the airplane as it accelerates so we know that to calculate resultant Force we can use the formula that we use f equal to m a and mass here is equal to 2.5 times 10 to the power of 5 multiplied by the acceleration we calculated in fact it's deceleration but you can use the same thing and then we can just plug that value in to a calculator and then we'll get 400 000 Newton all right so that's it and calculate the momentum of the ever plane when the speed is 6 meter per second so to calculate momentum we use the formula P equal to m v so mass is equal to again the same value multiplied by 6 which is the velocity so if I were to do that in my calculator I'll get 1.5 million which is 3 4 Newtons sorry kg meter per second inverse so that's basically the answers um so next the next question is about how to write sort of like an essay answers explain in terms of the momentum of the molecule why the Trap air gas exerted pressure on the wall and for this question I'm just going to show you the answers because the molecules the eye molecules here collide with the wall and because of this we know that the speed of the momentum or we can see the direction of the momentum also changes that results in the momentum of the molecule changes and this causes a force and a force spread out over the wall to create pressure all right so that's the question so let's move on to the last subtopic here which is on scalar and Vector quantities so in physics we will learn different types of terms like acceleration velocity and all of this term can be categorized into two categories so first we have the scalar quantities followed by the vector quantities scalar quantity is a quantity that has magnitudes but has no Direction whereas the vector quantities they contains Direction so what I here I have an example some examples for instance there's no Direction involved in the following quantities here like time speed mass energy temperature whereas um something like force it can be either to the left or to the right or upwards or downwards so direction is important therefore force is a vector quantity acceleration they can either increase in speed or slow down same goes to momentum feel strength we'll talk more about this in the following chapters so that's basically the difference between scalar and Vector quantities so here we have a note here force is a vector quantity so it's important for us to know how to calculate the resultant Force when multiple Force are added together so if I have a force towards the right of 600 Newton and 300 Newton on the left hand side I'm gonna have 300 Newton resulting Force towards the right this is when Direction comes in handy because direction towards the right and towards the left is going to be two very different things and let's look into I believe this is the last question and I'll drag with three forces acting on its shown below I have an upward force of 75 Newton plus 35 Newton so in total I have 110 down upward force and the downward was 200. what is the resultant Force so downward force is 200 Newton and upward force is 110. so we know that there's a resultant force of 90 Newton downwards so the answer here should be a and that's the end of this chapter it has been a pretty long video and I hope that in this chapter we have learned the following terms let's go back to what we have um we learned what are the different types of forces available and how the specific type of force gravitational force work and how the three terms Force methods and acceleration they're all contributes together and also momentum impulse and the differences between scalar and Vector quantities and thank you so much for watching I'll see you in the next video where I will explore topics on moment