[Music] hey everyone welcome to homeschool hope everybody are doing good and today i am with one of the important chapters of class 9 science that is forces and loss of motion so this is one of the smallest chapters of class nine uh i'm going to cover this chapter in two videos this video includes everything about concept clarity i do cover all concepts of the chapter in a detailed way theoretical part i'm going to cover now in my next video i will try to complete all the problems that can be asked from the chapter i do cover exercise problems too okay so don't forget to watch these two videos on a chapter so coming to today's video let's discuss every concept in a detailed way see already chapter number one to chapter number eight are available in our channel if you have not yet watched video links are provided in the description you can go and check it out okay so coming back to the chapter force and loss of motion so first we will try to understand everything about force what is a force what are the units of force what is the formula for force what are the different types of forces right so all of them we will try to discuss and later we will go for newton's laws of motion there are three important newton's laws of motion all of them we will discuss in a detailed way and finally we will go for the concept of momentum and conservation of momentum okay so uh three major aspects we are going to study in a chapter one is all about forces the other one is three newton's laws and the third concept is about momentum and conservation of momentum fine so coming to the first aspect of the chapter that is force so let's understand what do we mean by force okay see force is everywhere see without a force actually no object moves isn't it see how does a car moves or how does a bus move and can you tell me uh see i am moving this chalk piece on a board right see how is this chalk piece moving actually on a board or uh i kept the chalk piece on my palm initially it was at rest i say now chalk piece is at rest but now at one end on one end i apply force you see with my finger on one end you know i am pushing this chalk piece so that chalk piece is moving right say if i have to move you know something like this what makes me moving you know what causes motion so motion in the sense movement of an object isn't it so uh if an object have to move you know what is the reason behind that can you all able to guess definitely force okay so i can say that force causes motion causes motion see if i do not apply force if i don't push this chalk page will it move never right if a car is moving you know engine is the reason engine is actually pushing the car to move right so everywhere force is involved that is the reason uh objects move from one place to another place otherwise they continue to be at rest isn't it okay so now what is this force in short we can define force as a push so this is what the definition of force that i am giving you a push or pull acting on an object acting on an object is called you know force okay so if i ask you can you all see a force or can you all feel a force can you all experience a force right what's your answer generally i say no we cannot see force right say for example i am applying force on one end right okay can i see that force no i actually cannot see the force i cannot feel the force i cannot experience the force then we can only see or observe the effect of force okay so this is very very important guys we can only experience experience effect of force effect in the sense outcome outcome of force okay see after applying say once you apply a force what is the outcome outcome is the chalk piece is moving the object is moving right say looking at the outcome we can say that yes this much is the force applied that much is the force applied and everything okay so we can only feel or experience effect of force okay so what do you mean by effect of force i mean to say once you have applied force on certain object what is the effects uh that you can observe or experience okay so that is what i'm going to list here so the first one is if an object is at rest you know after applying force what is the effect it moves right so object at rest starts moving starts moving so this is one of the effect that we uh observe in a day-to-day life right object initially it was at rest but once i apply a force how do i know that force is applied on one end of the chuck piece it's because the object is moving right so that is a proof effect in the sense proof that a person has applied force on a certain object because force cannot be seen cannot be felt but how do you know that force has been applied on an object it's by observing these effects okay so if an object is at rest it starts moving so this is one of the effect of force right the other one is just opposite say uh a moving object right say for example i'll move chalk piece like this like this if i want to stop it i apply force only then it stops right so with my fingers uh uh with some force i'm i'm just holding this chalk piece right it was it was moving with force only it was moving because i have applied some force and again it got stopped because i have applied another type of force isn't it so a moving object moving object gets stopped stopped okay so this is another effect of a force and second one speed of an object changes speed of an object changes right suppose a car moves with some speed right so uh when you accelerate the car it moves with higher speed so accelerating in the sense what you are actually giving force okay so you are actually applying force there so that is why cars speed increases gradually right so uh when you apply a force on an object you know it can go with much speed say for example with little force you see this chalk piece moves very slowly because very little force i am applying but you see now the top piece is moving very fast because much force i have applied right so by changing the force the amount of force that you apply on an object speed of an object changes so this is another effect another outcome that you can observe whenever force is applied on an object okay and coming to the next effect direction of an object changes direction of object changes okay so uh actually speaking force is a vector quantity guys okay so remember force is a vector what do you mean by vector vector is such physical quantity which have both magnitude and direction quantity which has both magnitude and direction okay so such a physical quantity is called uh what is that vector and magnitude in the sense what amount direction in the sense uh you know what in which direction you are applying force that also matters a lot okay see magnitude means how much force you are applying little or much and in which direction you are applying because the object moves uh in the direction where you apply a force right say for example i am applying force in this direction on the chalk piece that's why chalk piece is moving in this direction but now you know i apply force in the opposite direction when i apply force in the opposite direction the log base moves like this so you know in what direction the object moves always depends on in what direction you are applying force okay so that's why you know force is always a vector quantity so whenever you apply force sometimes direction of an object also changes and third one dimensions of an object dimensions [Music] object changes so what do you mean by dimensions it is shape of an object changes if you take a spring you know you expand a spring initially the spring has certain shape right but when you expand how do you expand with some force right so when you expand that means uh when you expand that with the force its shape changes right like that dimensions in the sense shape shape of an object changes uh with the application of force direction of an object changes with application of force so all these things will change you know these are actually outcomes of force so looking at the outcome observing the outcome one can say that yes some push is taking place on an object or some pull is taking place in an object okay so that's why we say force is actually a push or pull acting on an object right so hope you are clear with the basic aspect of force right and definitely this is very very important guys force is a vector quantity it has both direction and magnitude and remember force has got a formula which we write it as f is equal to m a here m is nothing but mass and a is nothing but acceleration and don't worry about this formula we will try to explore more about this formula actually this is a second law of motion okay we will again discuss how this formula has come don't worry now just the basic aspect so this is the formula for force right and the unit s i unit of forces newton sr unit of force is newton okay so about the unit also we will try to discuss more in the next coming aspects okay so this is much basic aspects you need to know fine and now we will go for uh different types of forces okay so everyone first let us understand about balanced forces and unbalanced forces so it's very simple suppose you have a box so this is a box right and this is your friend actually pushing this object with 10 newtons of force i told you newton is the unit of force okay so how much force he is applying on an object so it is 10 newtons okay so this is your friend applying 10 newtons of force okay and uh this is you this is you who is applying i mean you are applying 10 newtons of force from this side okay your friend is pushing this object with 10 newtons of force and you are also pushing this object with 10 newtons of force so can you tell me will the object move okay so you have applied you know the same force your friend is also applying the same force on an object to push okay so you both are trying to push an object you know the object will not move why because this force got balanced with this the force that your friend is applying is exactly equal to the force that you are applying on a box isn't it so the box will never move it will stay at rest isn't it so such a force is called as balanced force okay so when do you say a balanced force when a net force when a net force net force in the sense total force total force is zero okay then you will call it as balanced force balanced force you know actually on an object two forces are acting one is from this way the other forces from this way okay so both forces are actually equal right so uh you know here the forces are balanced so the net force or the total force that are acting on this object is zero so when the net force is zero you say uh the object is experiencing balanced forces okay fine and now you see another situation okay so this is your friend and who is applying 10 newtons of force on this object and this is you who is also applying 10 newtons of force okay see your friend is applying 10 newton 10 newtons of force and he is pushing it and you are also applying 10 newtons of force and you are pushing it in the same direction okay so you you are actually pulling it you are pulling it and your friend is pushing that object so here uh you know same direction both of you are applying the forces in the same direction right so here uh what are the total forces present 10 newton plus 10 newton right so all together 20 newtons of force is what experienced by this particular object okay so uh when the net force is not zero when net force is not zero then it is called as unbalanced force then it is called as unbalanced force okay see here the net force is 20 newton right so only when an unbalanced forces act upon an object it moves okay so this point is very very important guys object moves object moves only when unbalanced forces unbalanced forces acts acts on an object okay so when the forces are balanced the object will not move so in this case object object do not move right so when balanced forces are acting on an object object will not move so whenever the forces are unbalanced okay only then the object can move okay so what type of forces lead to movement of an object it is unbalanced forces okay fine so now i'll give you different situations and try to predict whether an object moves or not okay fine so this is a particular box right so uh from this direction i'm applying 10 newtons of force and you know like this i'm applying 10 newtons in this direction i'm applying 10 newtons of force and here from up i'm applying 10 newtons of force and from bottom also i am pushing with 10 newtons of force so post your answer in the comment section whether an object moves or not okay so how much is the net force here okay so how much is the net force and also tell me whether the object moves or not okay fine and now another situation you see so here from this direction i'm applying 10 newtons of force uh then from this direction i am applying 10 newtons of force so from up i'm applying 10 newtons of force and from bottom i'm applying 10 newtons of force okay so here let me calculate what is the net force if the net force if the net force is zero it is balanced force uh you know the object do not move right if the net force is not zero you know it is unbalanced force acting on an object uh in that case the object always moves okay so this is the homework for you you are commenting your answer in the comment section and this i'll explain okay so suppose you know if if this direction is a positive direction okay so force is a vector quantity right so i'll take uh moving right side is a positive direction and moving up side is a positive direction okay fine so here this is plus i'm i'm adding all the forces now this is plus 10 newtons okay and and this one is this is also plus 10 newtons okay and moving up is a positive direction so this force i can take it as plus 10 newtons whereas this force you see it's the force that is applied downwards right so this i will take it as minus 10 newtons okay so the 1 plus 10 minus 10 gets cancelled so total net force is 20 newtons so the total force is not equal to zero here isn't it total force is not equal to zero so when total force is not equal to zero it is called as unbalanced force whenever unbalanced forces act upon an object object moves so tell me whether the object moves in this case or not definitely the object moves okay so likewise you can calculate here also okay so take uh this direction and up okay these two directions are positive forces the other two directions are negative forces so that way you take down you can calculate like this and decide whether the net force is zero or not if the net force is zero it's a balanced force if the net force is not zero it's unbalanced only when unbalanced forces are there the object moves okay so this is the concept of balanced forces and unbalanced forces so now we will also talk about the different types of forces guys we actually have uh two types of forces one is a contact force the other one is non-contact force so i'll give you some general introduction about what do you mean by contact force and non-contact force okay so broadly forces are divided into two types one is contact force contact force the other one is non-contact force non-contact force okay so under contact force the very first variety is called muscular force so what do you mean by muscular force okay you see contact force is the the force that arises on an object when an object is in contact with another object suppose this chalk piece which is there on my palm initially at rest if i want this chalk piece to move on my palm i should touch one end of the chalk piece with my finger and with my finger i should apply force i should push this only then it moves right so what type of force it is how how this chalk piece is experiencing a force when this chalk piece is in contact with my finger okay so the force arises or the force experienced by the object when the object is in contact with another object okay got to know so such a force is called contact force clear fine so contact forces are again various types one is muscular force uh you have normal force you have tension force you know all of them you will discuss in much higher level uh now i will try to uh mention only two types of contact forces one is muscular first the other one is frictional force so you should definitely understand about frictional force here okay say muscular force in the sense uh just this say the chalk piece if it has to move if a chalk piece has to experience a force it should be there in contact with my finger right so this with my muscle with my uh you know finger i am actually uh pushing this chalk piece forward i have applied force on this chalk piece so that it is moving forward right so such a force we will call it as muscular force say you are lifting something say uh chalk piece was here and i am lifting the chalk piece right so i actually contacted i have touched this chalk paste with some force i am lifting it up right actually here my muscles are working uh to create this force okay so such a force is called as muscular force coming to frictional force frictional force is the force that opposes the motion of an object this is very important this is a kind of a force that opposes that opposes motion of an object motion of an object so such a force is called frictional force okay say for example uh you see if the surface the chalk piece if i keep it on a rough surface okay so will it move very easily no right even though i applied some force although i push the chalk piece you know it will struggle to move if the surface is very rough you know so such a force actually that a kind of force opposing chalk piece to move a kind of force that is not allowing chakras to move freely you know such a force is called as frictional force okay so whenever you try to move your cycle or something some vehicle on a rough surface you know it will not move smoothly right because the surface will create you know a resistance uh for an object to move you know it will not allow an object to move freely so such a force such an opposing force uh is called as you know frictional force so frictional force is the force that opposes motion of an object okay fine so uh these two are very very important type of contact forces and non-contact force under non-contacted force you will have three types of forces one is gravitational force gravitational force which you will study it in the next chapter don't worry say actually whenever i throw a chalk piece down say i'm throwing a chalk piece automatically it falls on a ground actually the earth's gravity uh you know which we will call it as gravitational force that is making the choppies to go down okay see the moment i through this chalk piece it is going down only it's because the earth the earth force is pulling the chalk piece towards it okay so such a force is called as you know gravitational force okay so to act this force to create this force uh it's not that the object must be there in contact with earth right so it's not there in contact with earth but still when i through it it is going down okay so such a force that actually pulls everything towards the ground you know is called as gravitational force fine and next is magnetic force magnetic force suppose two magnets are there i hold the magnets you know i i'll bring the magnets closer and closer what happens they you know they combine with each other right it's not that i should uh bring this magnet and i should touch this magnet only then you know they get attached with each other it's not that concept right so i hold them very far with each other you know but then they are you know they try to combine isn't it so such a force such an attractive force between the two magnets is called as magnetic force similarly we have another force called electrostatic force so electrostatic force is the force between the two charges so whenever you bring positive and negative charges near they automatically combine they get attracted towards each other right so such an attractive force between the two charges uh is called as electro static force so all the three forces are non contact force and frictional force very importantly this is an example for contact force okay so these are the different types of forces and now with this idea we will go for studying the three important newton's laws of motion coming to newton's first law it's very simple definition is written on a board say the definition says an object remains at rest or if an object is moving it continuously wants to be moving okay an object remains in a state of rest or in a uniform motion in a straight line unless an external unbalanced force is applied on it suppose this chalk which is there on my palm is at rest and it will be addressed okay so until unless i disturb it wants to stay at rest it is at rest it will be at rest right till till i apply some external unbalanced force okay only when i apply some external force it starts moving otherwise it will be at rest or you can take a moving car okay so moving car moves moves and suppose if it is moving in a straight line with uniform velocity okay so it it always moves with uniform velocity till you increase the speed or till you apply some bricks okay so when you apply brake it will try to stop otherwise it continuously moves with the same speed that you are driving with right so this is what we mean by first law of motion so an object it can be of any object it if it is at rest it will be at rest okay it wants to be at rest if it is moving it wants to be moving until and unless you apply external force onto it only when you apply some external unbalanced force only the object starts moving or the object's position will change isn't it so this is what we mean by first law of motion newton's first law of motion and this first law of motion is also called as law of inertia law of inertia so now we will talk about what do we mean by inertia see there is a similarity between uh the definition of inertia and newton's first law first let me write what actually inertia is it is the tendency of an object tendency of an object to be at rest to be at rest okay or to be in a motion okay till till an external till an external force applied on it so if you look at the definition of inertia and newton's first law it seems to be similar right it is that ability of an object or you know it is the resistance of an object to be at rest okay if an object is at rest it wants to be at rest rest all the time until and unless you disturb it until and unless you apply some force it wants to be at rest or if an object starts moving you know it wants to be moving moving always until and unless you apply some external force only then some change can take place okay so it is that tendency of an object to be at rest or in a motion till an external force applied on it so that tendency or resistance of an object is called as inertia see guys the best example to show inertia uh i took a tumbler a glass tumbler and i took a cardboard piece and this is a coil okay and this coin i'll place it on this cardboard okay and this coin actually it is at rest it is at rest and it wants to be at rest i can prove that okay see now what i will do is i will just apply some force on a cardboard and i'll push the cardboard cardboard will flow away okay but the coin will not go along with the cardboard coil coin is not going with a cardboard instead it is falling into the tumbler that means coin is at rest it wants to be at rest it doesn't want to move that's why even when i apply some force on a cardboard it's not moving with a cardboard it is there on a cardboard but it's not going along with the cardboard it is falling into the tumbler okay so this is what we call inertia inertia is there with every object it is the inbuilt property i can say inertia is a kind of laziness okay so every object has a certain level of laziness see as human being we do have certain amount of laziness so when we sit in a sofa and watch tv we just want to sit and watch every time every time until and unless somebody comes and disturbs us until and unless if we have any work right so inertia is like inbuilt property of an every object okay so if an object is at rest it wants to be at rest if an object is moving it wants to be moving moving it doesn't want to stop okay so now let's see i will just throw this cardboard okay i will just apply some force on a cardboard cardboard will slope away but the coin will fall into the tumbler you see right see i push the cardboard it it fell down but the coin did not go along with the cardboard instead it fell in the tumbler that means coin was at rest on the cardboard it wants to be addressed okay so it doesn't want to go away with the cardboard piece okay it is falling where it is there in the tumbler right so this is the best example of inertia and one more example i can give you suppose you are sitting in a bus okay so uh suppose there is a bus okay so there is a bus and you are sitting you are sitting in a bus okay and the bus is at rest you just went and you sat in your seat the driver came he will start the bus and he'll start moving the bus so will you stay at rest or will your body's movement changes so the moment the bus starts going forward okay for a fraction of time you go backwards imagine you're sitting in a bus the driver just now started the bus so the bus will try to move for a fraction of time you move backward that jerk you will observe in your body that means your body was at rest it wants to be at rest it's not ready to go along with the bus so that's why for a moment you you will just go backward okay so this is uh this is because your body has some amount of inertia your body is so much lazy it is at rest it wants to be at rest okay so it is not ready to go with the bus okay so that's the reason you go backward you will fall onto a seat backward right so uh this is what the concept of inertia so every object has inbuilt uh inertia guys it is a property of an object okay so that's why it is a tendency of an object to be at rest if it is at rest it wants to be at rest always if it is in a motion it wants to be in a uniform motion okay so uh till an external force applied on it okay so that is called inertia and actually uh you know mass is a measure of inertia guys mass so you have mass is a measure of inertia okay so if i ask you a question does everybody has same amount of inertia no okay say an object with more mass has more inertia an object with less mass has less inertia okay say uh for example and every hefty person comes and stands beside me okay see uh if somebody pushes both of us who will fall first i will fall first the heavy hefty person stands like that only it's because he is more heavy right so the person is more hefty so it's like the person with more mass or an object with more mass has more inertia so remember this point guys it's very very important an object an object with more mass has more inertia more inertia it's very difficult uh to change the position of heavy objects right you will have to apply more foods to change their position right or to make them moving right so that's why an object with more mass has more inertia right say for example i have a chalk piece and duster heavy duster so which one will have more inertia duster will have more inertia big choppy small chalk piece big chalk piece will have more inertia thin person fat and hefty person so fat and hefty person will have more inertia okay so uh inertia is actually uh you know mass the the quantity that is the mass is a good measure of inertia or mass or inertia is nothing but the same okay so weight is again different okay so about the weight we will talk uh it in the next chapter don't worry so mass is actually it's a measure of inertia right so this is all about inertia and newton's first law so newton's first law is very very simple it can also be called as law of inertia also it's because so both are similar here look similar so what is newton's first law an object remains at rest or if it is an emotion it wants to be in a motion until and unless some external unbalanced force acted on it okay fine so we understood everything about newton's first law now we will go for newton's second law of motion coming to newton's second law guys it is the application it it is the next level of first law so uh in our first law we have discussed that until unless you apply force the object will not move right or for a moving object when you apply force it moves faster it moves faster and to some extent we understood the amount of force uh that we require to apply on a moving object depends on mass isn't it more mass you have for an object more force you have to apply if you want to move such an object isn't it so based on that we have this newton's second law let's write it in a point wise newton's second law so what i write in a simple terms is force required for an object to be in a motion force required for motion of an object for motion of an object okay always depends on depends that force actually depends on mass and velocity mass and velocity of an object okay so this is really very very important or in other words uh we can say that the rate of change of momentum so a new word for you the rate of change of momentum is directly proportional to is directly proportional to unbalanced force or let me write it like this proportional to applied unbalanced force on it okay so you have a new word here momentum okay so momentum say in a simple terms our second law is nothing but uh force required for a motion of an object okay mainly depends on two factors it depends on mass of an object and it also depends on velocity of an object okay so this is really very very important to understand a small bullet which was having very less mass okay so travels so fast in the air right it's because velocity is very high so you know what all these are the bullet a small bullet traveling in the air with very high velocity this is application of second law itself right so various things that we see it in a day-to-day life is based on the newton's second law okay so always the force required uh by an object you know always depends on the mass and velocity and you know the product of mass and velocity itself we will call it as momentum product of mass and velocity is called momentum body will be product it's a multiplication so mass and velocity is called as momentum momentum is represented with the letter p okay so momentum is also a vector quantity it has got the both magnitude and direction okay so product of mass and velocity is called momentum and you see the statement the rate of change of momentum rate of change of momentum is what suppose you have an object suppose you have an object with mass m with mass m so this object has initial momentum initial momentum p1 okay so the object has final momentum final momentum p2 right so what do you mean by rate of change of momentum it is nothing but change of momentum that is p2 minus p1 divided by t rate in the sense always something divided by t rate of change of momentum in the sense momentum divided by t is called rate of change of momentum so this rate of change of momentum is directly proportional to what force so this is a mathematical formula or formulation that i am doing based on the statement of newton's second law so according to a statement so this is something that is written in a sentence that i converted into mathematical format okay so force is always dependent on rate of change of momentum in other words the statements meaning is this only force required always depends on mass and velocity product of mass and velocity is called movement so rate of change of momentum is directly proportional to force so this is how mathematically we can write so what is momentum product of mass into velocity right so mass is anyway constant right so initial moment this is a final momentum that was a initial momentum okay so how do you write final momentum as m v2 v2 is the final velocity of an object okay minus m into v1 is the initial velocity of an object divided by t okay is directly proportional to f so m you take it common what do you get v2 minus v1 by t which is directly proportional to f so here you observe v 2 minus v 1 by t final velocity minus initial velocity change in velocity divided by time is nothing but acceleration so m a directly proportional to f so to remove a proportionality sign we have to introduce a constant called k so m a k is equal to f so proportionality constant k is always considered as 1 so f is equal to m a so this is the mathematical formula of newton's second law so this is the most important formula you need to remember formula number one okay so this is formula number one f is equal to p2 minus p1 by t next formula number 2 is this f is equal to f is equal to i have written i can write directly because k is the proportionality constant its value is 1 so f is equal to m into v 2 minus v 1 by t this is second formula this is the third formula so based on these three formulas uh problems can be asked that we will solve it in the next video okay so this derivation is also important guys so this can also be asked for two marks so this is really very very important so this is how uh this formula is derived this is what we mean by you know second law of motion okay mathematical way of telling uh second law of motion so force is always directly proportional to mass and acceleration okay so more the mass of an object more is the force that you will have to use okay and uh you know the more force you apply more will be the acceleration of a body acceleration of a moving body okay so that is what the meaning of this particular formula right and uh you know the unit of force actually uh mass unit standard unit is kg acceleration unit is meter per second square right so this is the unit of force this unit we can also call it as newton okay so 1 newton is always is equal to kg meter per second square actually okay so that is how you have got newton as the unit for force right so this is all about the second law of motion now we will go for third law of motion which is very simple see guys newton's third law is very very simple okay so for every action there is an equal and opposite reaction right for every action there is equal and opposite reaction equal and opposite reaction is called newton's third law right for example you take a ball with some force you hit the wall that is there in front of you with the same verse it will come back to you right so almost with the same force but in a different direction it is coming back to you right so one more example i can uh tell you say uh you have a rowing boat okay so rowing boat so here a person is standing and he want to jump you know this is a sea and this is a big rock uh he want to jump from this boat to this particular rock what will he do he'll stand at the tip with some force you know he'll try to jump so when he jumps with some force so here the force is acting in this direction right because the person is jumping in this direction so with some force he is jumping onto this particular block or a you know a big store so the force is acting in this direction but at the same time you can observe one thing when he jumped standing on the tip of a boat the boat also start moving in the opposite direction right so there is some force applied on this object also but in the opposite direction right so this is what is a proof for newton's third law so in simplicity i can tell you say if one there are two object so if this object exerts a force on this is object a and this is object b so if a object exerts a force on b object b object will not sit quite it will also exert force on a object okay so uh this is what we mean by third law for every action see this object is exerting a force on b object so this is action okay there is equal and opposite reaction so b object also will exert a force so that is what we call reaction this is action this is reaction but you see the force this force is in this direction and the b objects force is there in opposite direction right so for every action there is equal and opposite reaction so that's all about the third law and coming to the last concept of the chapter conservation of momentum conservation of momentum okay so this is really uh something very important to understand we all have seen momentum is nothing but mass into velocity right so every moving object will have certain level of momentum okay so it is nothing but mass times the velocity okay so uh usually you know how big is the momentum or how small is the momentum depends on mass and velocity okay so every moving object will have certain amount of momentum and this momentum is highly conserved you cannot destroy momentum and you cannot create momentum do you remember law of conservation of energy energy can neither be destroyed nor be created right that is conservation of energy similarly conservation of momentum is nothing but momentum momentum can neither be created neither be created nor be destroyed okay nor be destroyed right so this is what we mean by conservation of momentum we can actually uh take one example here suppose if these are two balls this is ball a moving ball so both balls are moving balls okay so this ball is moving in this direction even this ball is moving in this direction this is ball a and this is ball b okay and this ball has a mass m a and this ball has a mass mb okay so it is moving with some initial velocity let's take it as ua1 and this is moving with some velocity let me take it as u2 okay fine so u 1 is the velocity of ball a and u 2 is the velocity of ball b okay fine and now both of them have collided okay so they were moving two balls were moving at some point they collided they collided and after the collision they start moving okay so they both collided at some point after the collision you know they started moving they started moving again okay fine so after the collision whatever the mass of a ball is there that remains as m a and after the collision whatever the mass of b ball is there that remains same that is mb okay but will the velocity remain same no with u1 this ball a was moving after the collision maybe its velocity might have changed let me take it as v1 okay so here again ball b's velocity also will change it is not similar as initial velocity so let the velocity be v2 okay so what is the momentum here before collision what is the total momentum here total momentum momentum of this body is what mass into velocity now so m a u1 right plus i'm talking about total momentum total momentum before collision m a u1 plus mb u2 so this is the total momentum before collision before collision so this will actually be equal to total momentum after collision before collision they were moving with some momentum collided after donation they started moving again okay with different velocity but mass is same okay so after collision the momentum of these bodies is m a v1 plus mb v2 right so this is the momentum after collision this is the momentum after collision right so total momentum before collision is equal to total momentum after collision okay so this is what we call the conservation of momentum just like conservation of energy and mass momentum is also conserved you can neither create momentum nor describe momentum you can only change it it all depends on uh you know it directs towards the force that's all okay so uh this is all about the chapter guys so with this i completed all the concepts of the chapter in my next video i will come up with all the problems uh that you get from a chapter let me solve all uh exercise questions and other different varieties of problems from the chapter okay so do subscribe our channel to learn the concepts in the easiest way and in a detailed way thank you so much see you all in the next video [Music]