Laws of motion/Grade-11/JEE/NEET/Physics

Added: 2026-05-28

[00:01:34]Hello students, welcome to the student the brand. This is sir.

[00:02:17]Hello students, welcome to the student brand.

[00:02:28]Welcome to the student the brand. This is sir. Today topic is loss of reflection. Okay, loss of reflection.

[00:02:38]Let's discuss about it. Loss of reflection.

[00:02:49]Loss of reflection.

[00:02:54]Okay.

[00:02:55]So in this topic we will discuss particularly about So in this topic we'll discuss right so first one inertia.

[00:03:12]So in this topic we will discuss about inertia right inertia. So what is inertia?

[00:03:22]What is inertia?

[00:03:26]So I'll give few examples. I'll give few examples by that you'll get to know.

[00:03:36]Point number one, the book is placed on the table.

[00:03:43]So before that table is at rest.

[00:03:47]Okay. So point number two.

[00:03:52]Point number two, fan is at rest.

[00:03:57]Okay. So when you switch it on, the fan continuously moving. Once you switch it off, the fan still it continuously in motion.

[00:04:10]And one more example. So I'll give few examples.

[00:04:14]With the help of those examples, I will explain inertia.

[00:04:19]And one more example.

[00:04:24]So the carum coins are there right? So carum board the coins are there. So they are placed like this in vertical position. So if you hit the bottom coin of the coin. So like all the coins are placed. If you hit the bottom coin.

[00:04:41]Okay. So the bottom coin will move forward. The remaining coins will stay in the same place.

[00:04:50]So keep in mind and one more example if you beat the stick sorry if you beat the carpet with stick if you beat the carpet carpet is there right so carpet with stick the carpet will move the carpet comes under motion so the dust particles are there in the carpet will fall down due to inertia of rest.

[00:05:23]And one more example if you observe the dust. So white like a chalk paste duster is there right. So after arising the dust particle chalk paste dust particles will stays on the duster. If you hit the duster okay with stick like that. So duster comes out so dust particle will falls down. So one more one example and so I'm in the running bus. Okay.

[00:06:00]So when we are in the running bus running bus so what happens suddenly the bus stops.

[00:06:13]Okay. If suddenly the bus driver applies brakes.

[00:06:19]Suddenly bus driver applies brakes.

[00:06:23]Then what happens? Suddenly bus driver applies brakes.

[00:06:27]So we fall forward.

[00:06:32]Forward forward or backward. I'll give an example. In which direction we move forward or backward? in which direction we will fall forward or backward.

[00:06:44]So when suddenly bus driver applies brakes.

[00:06:50]So observe carefully our legs are I'm sub so my legs are touching the ground. Okay. So my body is moving in.

[00:07:02]So the body is in moving condition. So when bus driver applies brakes so legs are contact with the ground of the bus like okay then so legs are trying to come to rest but upper body is in motion right so we fall forward and one more example so when the bus is at rest so we are standing suddenly the bus start moving Our legs are contact with the bus to the ground surface. Then so along with the bus our legs trying to move in. So trying to move so our upper body stays in the same state. Then we'll fall backward.

[00:07:51]Which direction we will fall? Backward direction we'll fall. Understood or not?

[00:07:57]We'll fall like this. Oh my god.

[00:08:00]So I hope it is very clear. So and one more example I'll give if you drop the object if you drop the object okay so the body is in motion so zoom it but I can't able to do in real live right so maybe in the video I can able to slow the video and make it zoom how the object is falling we can do it but in live class I can't able to do it right so but at least you can imagine like that so the body This I'm dropping the body. The body is moving down.

[00:08:37]So imagine understood from here to here you have to imagine. So from this point to this point the body is so I'll show with the hand. So hand is not know so you are not observing the hand only the object you observing slow in slow motion. Okay. Without graphics. So there is no graphic now. So there is no graphics. So real real time I'm okay I'm explaining. So that's why the body is falling down falling down falling down. Understand? You are at this point moving at this point moving at this point moving at this point moving. Is there any external force sir? Aulation is gravity acting on it.

[00:09:25]So aulation gravity will be acting on every object.

[00:09:30]Okay, even the dust particles if you dust the dust particles are coming down.

[00:09:33]Even that time also when you are standing aation due to gravity when you are falling forward or backward action with gravity is acting. So the fan is rotating that time also aation due to gravity acting. And one more example when you are taking the long jump. So the person is taking long jump. What happens when your the person is taking long jump he will move for backward little backward and he will run from that place that time onwards. So from that point onwards he will run like this. He will run he'll get that uh inertia. So he'll get that motion then then.

[00:10:13]So then what happens? He'll start. So he will take long amp. So in the middle of the air in the middle of the air. Okay.

[00:10:21]So he will continue that motion. So he he gained that energy right. Okay.

[00:10:28]Like that. So he started moving forward like this like this. So he got that energy. Okay. He got that momentum. Then what happens? He will take long jump.

[00:10:39]Okay. So like that. Understood or not?

[00:10:43]He continues that motion even in the middle of the right. Yes. And one more example I'll take. So take a stone tie to the thread and will then leave which direction.

[00:11:11]So along tangential direction it will move right. So even you can observe the throw ball can observe the throw ball.

[00:11:19]So you will they will apply force like this. They'll apply force they will take like this and they will throw like this along the tangential direction.

[00:11:29]Understood or not? And even one more point one more example we can see uh so in the like uh what we can say like like a functions like a what we can say exhibition yes exhibition. So in the exhibition the person who is moving on the bike so he will take like in the well like like a well model like it's like well type like a cone shape cone shape it is not exactly straight so it will be somewhat inclination so it will be somewhat inclined right so you'll take like this okay so it move so if you if you if he comes out of the ring then he will goes along the tangential action.

[00:12:16]Understood or not? And one more example.

[00:12:20]So you can see during winter time the water droplets the water droplet along the uh so you can observe cycle t back side of the cycle tire. So the water droplet moves along tangential direction.

[00:12:36]Okay. And one more example.

[00:12:38]So I suppose so under uh like experts so this must be done under some expert people like that will say no yes or no.

[00:12:50]So caution okay so people who are doing these type of activities must be observed by the expert or must be observed by the people or must be take some precautions like that. Okay.

[00:13:03]Normally the person who is coming or getting down from the running bus suppose I said I so I didn't mean you have to go and try this experiment with some experiment some people are there some guided person some expert person I'm not telling like that so if suppose so it's like imaginary things right so suppose if the person is getting down from the running bus what he has to do so immediately has to jump out and move along the particular direction.

[00:13:33]Understood or not? So if he's not moving in the particular direction, if he's not moving along the particular direction, what happens? If he if he want to stop immediately himself, then what happens?

[00:13:46]So he will fall and roll in the same direction. Okay. So due to inertia of direction, so he has to move in a particular direction otherwise he couldn't able to stop himself. So immediately so it has to continue that motion understood or not and so so I hope uh maximum uh I given so many examples right related to energy of rest inertia of motion inertia of direction.

[00:14:16]Now one by one we will discuss inertia of rest.

[00:14:21]So what is inertia of rest? Unless external force acting on it the body does not move from its position. Simple point. The body opposes the change in motion.

[00:14:34]Simple. So we want to sleep in the early morning. Okay. Suddenly alarm rings. So what we will do? So generally general cases. So I I'm not saying extraordinary cases like that. So the one who has determination compulsory has to get up and do that. Even for every person, everyone some inertia will be there that is okay sometime at least. So I have to stay sometime on the bed then I will wake up that so the body opposes the change in motion. So we couldn't able to wake up the couldn't able to wake up from the bed. So somewhat inertia will be there.

[00:15:19]So that is called inertia of rest. Okay.

[00:15:22]Coming to the inertia of motion as I mentioned once you switch off the fan so fan still continuous once you off the fan once you off the fan still the fan continuously in motion and one more example you observe so once we get up and do the work we'll continue doing work so we don't want to go to back and sleep okay so once you are in uh work so it will continue.

[00:15:53]Understood or not? So that is also inertial only. Yes. And one more example energy of direction as I mentioned energy of direction. So when you are getting down from the running bus he has to move in the particular direction until certain distance. After that only he can able to stop otherwise he couldn't able to stop himself.

[00:16:13]He definitely couldn't. If he trying to stop immediately then what happens? C will fall and roll like a ball.

[00:16:22]Understood? Like a football he will fall and roll like this. Okay. Someone should stop him. Okay. Otherwise he will do rotating, rolling, moving on the ground and if anything object comes then he will hit the that object and stop otherwise there is no option. Understood or not? So otherwise so he could slowly he has to come out and he has to come out and move in the same direction at a certain distance then automatically he can able to stop himself right so this is about inertia of rest inertia of motion inertia of direction okay as I said object object wise if you taking the take a stone try to the thread and will like this in a circular motion and leave it moves along the tangential direction along the tangential direction. If you leave the if you take the arrow leave it moves along the tangial direction in one direction. Yes or no? So like these examples we can say for inertia of rest inertia of inertia of rest.

[00:17:36]Second one, inertia of motion.

[00:17:39]Inertia of motion.

[00:17:42]And coming to the third one, inertia of direction.

[00:17:48]Inertia of direction. I hope it is very clear.

[00:17:52]Understood or not? Inertia of motion, inertia of rest and inertia of direction.

[00:17:59]Right? Yes. So next one we will discuss about contact forces and non-cont forces. So next one we will discuss about contact forces.

[00:18:12]Contact forces. First one. Coming to the second one is non-cont forces.

[00:18:20]Non-cont forces.

[00:18:23]So coming to the contact forces.

[00:18:27]What are the contact forces? By if two bodies are contact each other, if two bodies are close to each other, if two bodies are attached or two bodies are contacted, then the forces are acting that time that time in that case we can say contact forces. Sir, what are the example for contact forces?

[00:18:50]Like we can say friction. So I want to move on the ground. Okay. So I'll tell one story.

[00:19:01]So the person very serious okay story a very very serious story. Okay. So uh two two persons are talking each other person A and person B. So I'm not giving any names just person A person B like this that's enough. Okay. So if you think A is also name I can't do anything. So just I'm telling person A person B that's enough. So person A is telling so I am I am very brave person.

[00:19:33]Okay. So I am the bravest person in the world. So I can do any challenge. I can do any activity. I can do any work. Like that he will tell to person B.

[00:19:45]Huh? You will do any work. Huh? You're the bravest person. Okay. Okay. I'll give one challenge. You do one thing. So during night time. So go to that ground and uh stay 5 minutes and come to me. So I'll stay at uh 100 m away from that place. So there is a dark place there's a ground. So dark dark place will be there. So you go and stand that place and come to me after 5 minutes then I will say you are the bravest person, you are the strong person, you are confident person, you are a courage person. I will believe I will accept. So I'll do the same thing. I'll prize you throughout the year only year that's enough. So what challenge you are giving to me?

[00:20:39]That is very small. Okay. So I will do anything. I will do any challenge. That is very ch small challenge. Okay. I will I will do C like like this. I will do it. So he is telling to person B then person B h okay okay do it do it we'll see so that night he went to that place okay he went to that place and stood 5 minutes there and uh started moving started moving he couldn't able to move forward oh my god she fries trying to scream came trying to shout doing everything what he can do to you knowh shout like that.

[00:21:29]Okay. So somehow he managed to escape from that place and uh okay so reached to person B. So next day morning he went to that place and uh saw that so nothing is there. So there is a stick like a tree tree fell down in that place. There is a stick. So that stick is attached to his uh shut.

[00:21:53]Okay. So it is pulling. Okay. So so he is moving right. So he want to move forward but at the same time the shut is attached to that uh stick right. Then he is trying to move forward. So the stick is pulling back him. Okay. So then so he he fooled by that stick. He became like that. So anxiety, so tension, so much tension like that. So next day you know, so person B said see that so that is your courage, that is our challenge. So don't uh no do over expectation, don't say over like a dils like that he said.

[00:22:36]Okay. So person A also accepted. So like that. So here what I'm trying to say is contact forces if the bodies are attached like this. Okay. The force will act. The force will act. So best example friction. You can take friction.

[00:22:52]Friction. Okay. So friction is there. So when you are moving forward, when you are moving forward, so when we are trying to apply force forward direction to friction. So when we are applying force on it, the friction will oppose the forward motion. Okay. So the friction between the ground and foot.

[00:23:12]Okay. Between the ground and foot, the friction will be there. Friction opposes us. So to not moving forward direction.

[00:23:21]Okay. So because sometimes see here friction is a friend. Friction is a flow. How how how it is when it is where it is like the first point is when it is. So if you take initially if you bought a shoe shoe so there are there are spikes to the shoe. Okay.

[00:23:42]After one year, two years if you observe so the spikes will reduce because of the friction. So if you're keep on walking, keep on running, keep on no okay so like uh walking, running, jogging like that. If you do then what happens? Automatically the friction because of the friction the spikes will reduce. So that is contact force only frictional force. Coming to the tensional force. So strength is so if your object is sank weight is acting downward direction tension will be there because of the uh contacting the bodies so both arc can contact then tension force will be there. So one more example one more example so actually now I'm giving the introduction once coming up so the level increases the level increases if you have patency please try to wait some time so uh the level increases one by one step by step okay so those uh level concepts also will Okay. Coming. Okay. Just wait some time.

[00:24:54]Okay. Right. Yes. So one more point where we are. Yes. So tension force, frictional force and normal force if the object is placed on the if the object is placed on the like a table. So weight is acting downward direction. So normally action is acting upward direction. So these are examples we can say. And coming to the non-cont forces, non-cont forces, gravitational force, gravitational force like electrostatic force, magnetic force, gravitational force, we can say gravitational force.

[00:25:36]If you drop the object, if you drop the object, okay, so without any contact, the body is moving downward direction.

[00:25:43]The body is moving downward direction.

[00:25:46]Understood or not? Yes or no? So uh earth attracts each and every object towards its earth center.

[00:25:58]Earth attracts each and every object towards its earth center. So yes so after so apple fell down on the ground. So because of that this all much all loss are generated all created. Okay. So it start from questioning.

[00:26:21]So it it all start from questioning what exactly why it is, how it is, when it is, why it is like that only.

[00:26:33]Okay. So okay fine. Now leave it about it. If you go uh in that way so we'll go beyond the point, beyond the extension, beyond out of the topic we'll go. So leave it about it. So we'll be fixed, we'll be constrained, we'll be okay like we can see we will fully focus on a concept based later we'll see.

[00:26:57]Okay. So first come to the point gravitational force electrostatic force.

[00:27:03]Gravitational force if you if you drop the object always it it attracts towards it at center. If you throw the object, if you drop the object, if you throw a projectile or up, down, side, from height, inclined plane, any direction the body moves towards it center. So that's enough that is a gravitational force. Coming to the electrostatic force, take a comb, comb it and take the so you can absorb the piece of paper.

[00:27:29]Those papers will be getting attracted due to electrostatic force. And coming to the magnetic force. So magnetic force north pole north pole north pole north pole ripple or attract ripple north pole south pole attract south pole north pole attract. So south pole south pole ripple. So by these examples we can conclude that we can understand that two similar poles will repel. Two dissimilar poles will attract. Two similar poles north south north south repel. South north south attract. Okay. I hope it is very clear. So that is about uh magnetic force. So these are contact forces. So coming to the next one. Momentum mass into velocity. momentum mass into velocity. Okay. So next momentum I'm taking momentum momentum = P bar = mass into velocity.

[00:28:32]So P = MB bar P = MB bar. So I'm taking so here SI unit is KG m/s that is B bar SI unit. So momentum is a vector quantity. Momentum is a vector quantity. So we know that law of conversation of energy. Law of conversation of energy. Energy neither be created nor be destroyed. Energy neither be created nor be destroyed but it changes from one form to another form. Okay. So here law of conversation of momentum. Law of conversation of momentum. Momentum before collision equal to momentum after collision. So m_sub_1 u1 + m_sub_2 u2 = m_sub_1 v1 + m_sub_2 v_sub_2. So momentum before collision equal to momentum after collision understood or not even kinetic energy also. So yes one more question they'll be asking there there is important concept that is recoil velocity of a gun. Recoil velocity of a gun. Understood or not? So if you fire the if you fire so then what happens?

[00:29:46]Bullet will move forward direction gun will move backward direction. So when the gun is moving backward direction the direction of the gun is called the the velocity of the gun is called recoil velocity of the gun. Okay. So because of the bullet is moving forward gun will move backward direction. Okay. Action equal to reaction. So here L converation of linear momentum. So energy like momentum before collision equal to momentum after collision. Now you can observe here both bullet and gun are at rest. Both bullet and gun both are at rest position. That time this entire term becomes zero. This entance become zero here. So m1 v1 plus m_sub_2 v_sub_2. Okay. So m1 is the mass of the bullet. V1 is the velocity of the bullet. M2 is the mass of the gun. B1 is B2 is the velocity of the gun.

[00:30:40]Understood or not? So like this we can take. So that is recall velocity of the gun. Is it clear or not? So like that and one more example when you are in the boat. When you are in the boat, so there is nearby seashore. Okay. So there is a boat. So one more example also we'll take. So this type of questions they will ask. So here this is the boat. So here is a sheore. Okay. So the person is standing here. So, so initially m_sub_1 u1. So here m_sub_2 u2. So he jumped from boat to the shishaw. Okay. To the ground. Then what happened that time? So this is moving backward direction. He is moving forward direction. So that time also we will use law of conversation of linear momentum. M1 u1 + m2 u2 equal to m1 v1 plus m2 v2. Is it clearer? There are different kinds of problems we will ask. Okay. So based on a particular concept based on each and every concept there are number of questions they can ask. So that's why I'm I'm explaining the topic clearly and related to that what are the questions they will ask those questions also we will discuss right and like a cases and based on that what type of concept they will ask and so where exactly they will concentrate like that those questions we will discuss right. Yes. So coming to the next one law of conversation of kinetic energy. So what I mentioned law of conversation of linear momentum likewise law of conversation of kinetic energy also that is nothing but of m1 b u1² plus of m_sub_1 u1².

[00:32:25]Okay. of m_sub_1 u1² + of m_sub_2 u2² = to of m_sub_1 v_sub_1² plus of m_sub_2 v2² okay so converization of kinetic energy right kinetic energy before collision equal to kinetic energy after collision understood or not so if the two bodies are colliding each other so I'm taking here even momentum also I'm taking so m1 u1 So this is M_sub_2 V2.

[00:32:58]So come to the collision also this type of examples elastic collision, inelastic collision, one-dimensional collision, head-on collision. Okay. So like that there are different kinds of concept, different kinds of okay number of concept. So like in different ways, right? So like one by one we will discuss M1. So m_sub_2 after collision so you can observe m_sub_1 v_sub_1 m_sub_2 v_sub_2 understood or not I hope it is very clear. So before collision bodies are moving. So here u1 this is u2 okay m1 u1 m_sub_2 u2 after collision m1 v1 m2 v2 is it clear or not? Yes. So here law of conversation of linear momentum is there law of conversation of kinetic energy also will be there right?

[00:33:54]Yes. So based on collisions. So now we are discussing about impulse. So next topic is impulse. So see here impulse.

[00:34:06]What is impulse?

[00:34:09]Impulse.

[00:34:11]Okay. Okay. So impulse is nothing but large force acting in a small interval of time. Large force acting in a small interval of time. So best example. So just now I explain momentum. So mass into velocity. So initial momentum will be there. Final momentum also will be there. Right? So a batsman he will hit the ball with okay he will apply maximum energy on the ball in less than so very fraction of time he will know he will touch the ball means hitting the ball okay in a fraction of seconds he will it like this so if it is straight forward so it has to apply if it is backward then we can do it like so sometimes it may be so different understood or not so now impulse I = F into T F into T. So impulse we can take change in moment Mus U. So yes I know so we can take I = F into T right. So what is F? M A. So what is A? What is A? V - U by T. Substitute here. I = M into V - U by T. Okay. Into T. So t is remains same. Okay. I'm not changing the t. Right. Right. So now you can see here I = mv minus m u by t. So tt get cancel that's why = change in momentum.

[00:35:44]Impulse equal to change in momentum.

[00:35:46]Understood or not? So this one also we can take and this one also we can write.

[00:35:51]So according to the given data according to the given data. So impulse equal to change in momentum. final momentum and initial momentum. So I equal to F into T. So force into time force into time. I hope it is very clear. Right? So that is about impulse.

[00:36:08]So coming to the next one.

[00:36:12]So next one is Newton's first law, second law, third law. Newton's Newton's first law Newton's first law.

[00:36:29]So first law coming to the second law and coming to third law. Third law. So what is first law? So in the starting of the chapter in the starting of this class, so I mentioned so many examples about one concept. What is that?

[00:36:50]Inertia.

[00:36:51]Okay. So, first law describes the inertia. Okay. So, mass is a measure of inertia. More mass, more inertia. Less mass, less inertia.

[00:37:01]Understood or not? So, that's enough.

[00:37:04]And coming to the next one, Newton's second law. What is second law? So, F net external force is directly proportional to DP by DT. What is DP by DT? Change in momentum.

[00:37:18]S I know change in momentum F is directly proportional to MV minus M U by T F = K into MV - M U by T. So what is K? K = 1 either in S S any K = 1. So f = m v - m u by t then f = m you're taking common v - u by t then f = m a f= ma so new second law what is Newton second law second equal to mass into aation what is Newton second law f= ma mass into aation the net force acting on the body is equal to mass into aation that is about Newton's second law This is second law. Okay. So coming to the third law. What is third law? Every action there is a equal and opposite reaction. For every action there is a equal and opposite reaction. If you throw the ball on the wall again the ball returns back. Okay. So for every action there is equal and opposite reaction. That is called Newton's third law. What is that? Newton is solved.

[00:38:38]Okay. So coming to the next one. Coming to the next one. What is that?

[00:38:45]So we'll discuss about Lamis theorem after that friction. Right? So Lamis theorem if you are taking so here f_sub_1 f_sub_1 here I'm taking this the f_sub_2 and here f_sub_3. So opposite to f_sub_1 alpha opposite to f_sub_2 beta opposite to f_sub_3 gamma.

[00:39:10]Okay. So now you can see here f_sub_1 by sin alpha f_sub_1 by sin alpha equal to f_sub_2 by sin beta and f_sub_3 by sin gamma f_sub_3 by sin gamma. Understood or not?

[00:39:28]f_sub_1 by sin alpha, f_sub_2 by sin beta, f_sub_3 by sin gamma. Understood?

[00:39:35]Is it clear or not? Yes. Yes. Yes. Yes.

[00:39:39]This is about lame theorem. This is about lame theorem. So coming to the friction friction friction friction.

[00:39:51]So friction friction friction.

[00:39:56]So coming to the friction.

[00:39:59]Okay.

[00:40:01]So here one is static friction.

[00:40:04]Static friction.

[00:40:07]Static friction.

[00:40:10]So coming to the next one. Limiting friction.

[00:40:16]Limiting friction.

[00:40:19]Limiting friction. And coming to the third one, kinetic friction.

[00:40:26]Kinetic friction.

[00:40:28]Under kinetic friction again we have uh sliding friction.

[00:40:36]Sliding friction and coming to that rolling friction.

[00:40:41]Understood or not? Static friction, limiting friction, kinetic friction, sliding friction, rolling friction.

[00:40:50]Okay.

[00:40:52]Static friction. Static friction is a self adjusting friction. So what exactly the static friction? So what is friction? Friction is a friction is also a force. Normally friction is a force.

[00:41:07]Okay. which opposes the relative motion between the two object or two bodies or two surfaces.

[00:41:15]Right? So what causes the friction?

[00:41:18]Interlocking of irregularities. What are the irregularities? So if you observe there is no perfect smooth surface.

[00:41:27]There is no perfect smooth surface in the world. Okay. Some irregularities will be there. Some irregularities will be there. So here you can see. So I'm taking one surface. These are irregularity grooves. And here one more surface like this. So this irregularities are interlocking then friction will be generated. Friction will be created. Friction will be there.

[00:41:52]Okay. So this body I'm taking body A and body B. So when body is B is sliding over body A. So this because of irregularities. So because of the contacting of because of interlocking of this irregularist friction will be generated friction will be created.

[00:42:11]Okay. So because of that friction will be produced. So these two surfaces cannot move until unless so we apply force that is greater than this one the interlocking are irregularities.

[00:42:26]Okay. So uh so you're applying so you you're drawing the table table. So like this I'm applying the force on the table run. So table is not coming. Applying force not coming applying force not coming because irregularities are greater than we are applying force.

[00:42:44]Okay. So interlocking irregularities is more that friction will be more then still you're applying force not coming.

[00:42:51]Still you're applying force not coming.

[00:42:53]It's not like that we have to move at any cost. So I play then the body is ready to slot ready to move that time friction will be there.

[00:43:09]Do you understanding or not? So when the body is ready to move the body is at the edge edge of the motion. Then if you so normally if you take a small weight automatically it will go down. Okay small weight. So even if you're playing small for then automatically the body slot start moving. So if you take a small stone and place at the end of the inclined plane. So end end that is edge edge. So what happens? Okay. So I did so much hard work.

[00:43:45]So day and night day or night I did so much hard work. So much hard work.

[00:43:50]Trying trying.

[00:43:52]Okay. for getting my dream rank, for getting my dream marks, for getting my dream college, for getting into IAT. I did so much for getting into neat. So I did so much hard work day and night, right from the starting of the day onwards, starting of the day onwards, doing so much hard work, so much hard work. So So we are frustrated.

[00:44:20]So getting lot of hard work. So I'm not saying how many hours how many hours I prepared like that. I'm doing I'm doing so much hard work hard work hard work in and out in and out of the day. I did so much hard work. So we are at the edge of the getting into the rank. We are at edge of the getting into the dream rank.

[00:44:47]We are at edge of the getting into IAT uh need okay so at that time some people they will give up so enough so much hard work I did so we should we can't able to do it so let it be so then few people will draw so one person one person so it it should not it should not be like this. My story should not end like this. My story should be written in the great way.

[00:45:26]Okay. So my story should be inspiration story for everyone. I have to be an inspiration.

[00:45:35]Okay. I have to be an inspiration to reminding people those who are dreaming big, those who are coming with the great dreams, those who are coming with the great hard work. So yes, I have to show yes this is a possible the word itself it is saying impossible word itself it is saying I am possible then why can't I try? I will try whatever it happens I will try.

[00:46:03]then that person will become the success story right? Yes. So that is that until that time that edge if you do hard work that edge if you bear it all this day and nights hard work okay little more little more if you do definitely you will do it definitely you'll get it okay be patience so behold your tears okay so behold your tears until you get success so once you get the success then automatically you no need to show you no need to prove automatically it will be visible to everyone.

[00:46:49]Okay. Success stories will be written on the wall success stories will be displayed understood or not not failure stories.

[00:47:00]So if you want to be in the success story, if you want to be displayed as a success story as inspiration to everyone, so do hard work. Do hard work.

[00:47:13]Not like normal person. Do extraordinary hard work, extraordinary hard work, extremely hard work that can be seen by you only with your wisdom. Okay? Then you will get it. Being different, being odd, being so like uh so what we can say choosen.

[00:47:40]So being different is not easy.

[00:47:44]Okay. So there are many fingers will point out to be. So you see in the we can identify what we can say know odd numbers out.

[00:47:56]Okay. So the question itself it is there the one who which one are normal like looking similar. So no one will look at it the one will no the answer itself. So the question itself it is there odd identify the odd one out. See are you understanding? If you apply to the life it is sure being different, being creative, being your extraordinary field knowing uh extraordinary in your field it's definitely it's a odd one out. Definitely it's odd one out. Okay.

[00:48:34]So if you bear all the all the things definitely you're going to win. So why I'm saying all these things means so people will do so much hard work. Okay.

[00:48:43]So in middle of the path sometimes they will feel enough we couldn't able to do it there are lot many like external forces acting on it acting on it okay acting on it so we couldn't able to bear it so they feel like that so it is even though it is not seen by anyone okay it is seen by only him our heart yes or no so that couldn't be okay polished towards your uh goal towards your work.

[00:49:21]Okay. Take that paint, mold it and grind it and shape it and uh so make a stepping stones for your success so much.

[00:49:34]So why we are saying all these things?

[00:49:37]Yes. Because of limiting friction. Okay.

[00:49:41]Okay. So because of limiting friction I'm saying all these things. Okay. Come to the point. So actually so I'm applying force on the table. I'm applying force on the table. So still the okay still this table is not coming.

[00:49:54]Not coming. Not coming. You're applying force. You're applying force. Still table is not coming. So so it is not like that. It shouldn't be not like that. I have to move the table at any cost. I have to use my whole and soul energy to displace the object. So then I I started pushing the table. I started moving the table. Then the body the table start moving. So at the edge at the end of the at the edge of the body to ready to move ready to slide that point is called limiting friction. I draw the diagram just observe here.

[00:50:31]Okay. So yes that is about limiting friction and kinetic friction. So kinetic friction once the body start moving once the body start sliding the once the body is start moving so like the body is under motion then friction will be less so once you are succeeded so automatically you'll go forward because of that path because of that path is allowing to move forward that's enough so keep in mind be motivated so be energetic Always think about your goal. Always dream out our goal. So little more energy, little more work, little more extra effort it's required. 99 we can get but that one mark how much work you did for 99. So equal amount of work you have to do for getting that one mark to be a 100% to be one first rank air India all one okay understood or Okay. Done. So come to the point sliding. So if you talk, so we'll go. So it's like a flow only. So we can't stop it here. So it goes like that only. So come to the point.

[00:52:04]So sliding friction. So you can observe the constraint. Okay. constraint like windows you can observe windows. So one window is sliding over another one. So like that keep on sliding. Okay that time friction will be less friction will be less because uh that window is sliding over another surface right. So there is a there is a uh less time for interlocking the surfaces. When the bodies are at rest and the bodies are in contact then friction will be there.

[00:52:32]Friction will be there. Okay. So friction will be there. Understood or not?

[00:52:38]Interlocking of irregularities will be more. So friction will be more. So comes to the sliding so the friction interlocking of irregularities will be less means there is a less time to contact. Okay. Coming to the rolling so when the body is keep on moving when the body is keep on sliding understood or not? So there is no interlocking of irregularities still friction will be less. Now static friction is greater than the sliding friction. Sliding friction is greater than the rolling friction. Understood or not? At start at static friction. Okay. Starting friction is greater than the sliding friction.

[00:53:14]Sliding friction is greater than the rolling friction. So, so here in the rolling friction friction will be least compared to sliding. So, sliding friction is less compared to static friction. Is it clear or not? Okay. So, let's start the drawing the diagram. So, I'll draw the diagram.

[00:53:56]So here I'm taking like this and here I'm considering like this. So here is applied force. This applied force.

[00:54:06]Applied force.

[00:54:14]Applied force. And here friction friction and coming to here friction. So this one is fs = m into r f_sub_r fk = muk into r muk into r. Understood or not? I hope it is very clear. So this is the static friction static friction and this is the maximum value of static friction.

[00:54:53]Maximum value of static friction.

[00:54:59]Static friction. So that is called limiting friction.

[00:55:05]Limiting friction.

[00:55:08]Limiting friction. And here we are taking this one is a kinetic friction kinetic friction. Understood or not? So I hope it is very clear. Just check once.

[00:55:23]Just check once.

[00:55:26]Applied force, friction, static friction, kinetic friction. Magdal of static friction is the limiting friction. Kinetic friction when the body start moving. Kinetic friction. This is static friction. So this is the point where the body is ready to move. This is the point where the body is ready to slide. Okay. That is a maxwell of static friction that is called limiting friction. Understood or not? So I hope it is very clear. So coming to the next one.

[00:55:57]So one more example I'll tell. So like weight when we are in the lift.

[00:56:04]So this is very very important. So I'll explain this lift condition. So when we are in the lift, so I'm taking here reaction force is acting weight is acting downward direction.

[00:56:20]Understood or not? So if lift is moving with a constant velocity or lift is not moving. V is constant or lift is moving the constant velocity or lift is not moving that time r = mg r = mg. So if lift is moving with aation upward direction. So I'm taking here.

[00:56:52]So here you can take R1 and M1 sorry MG here lift is moving with aation A.

[00:57:04]Lift is moving with aation A. So reaction okay reaction force. So now you can see here. So R1 is greater than weight of the object.

[00:57:18]R1 is greater than weight of the object.

[00:57:21]So R1 - MG = M A.

[00:57:27]Okay. R1 = MG + M A.

[00:57:34]MG + M A. So when the lift is moving upward direction with aation A with aation A. Okay. So this is the concept right? So in the problem they will give values.

[00:57:48]So here I'm taking like this. So R2 so in each and every case different reaction will be there. So here the body is at rest. So where in the lift? So lift is at rest are move with a constant velocity r= mg. So if the lift is moving upward direction with accelation a so r1 minus c r. So as I said F= to Newton second F= ma this is the net external force acting on it this is mass into acceleration so F= to which force is greater reaction force R1 is greater than the weight of the object that's why R1 minus mg then ma will be the same because mass into aation so each and every time when you're drawing okay so when you're writing the equation we have to follow the Newton's second law okay so you have to Follow the Newton second law. So observe carefully. Now here if the lift is moving downward direction, if the lift is moving downward direction, what what exactly? Here weight is acting downward direction. So weight is greater than the R2 S. So each and every time as I mentioned this formula Newton second law we have to use. So F is the net external force acting on it. Greater minus smaller greater minus smaller. Okay. So, loss of motion, loss of motion topic.

[00:59:26]Okay.

[00:59:28]So now you can see weight is greater than the R2. So now you can see mg - r2 = ma mg - r2 = ma understood or not? So now we can see mg - m = r2.

[00:59:51]Is it clear or not? No. So this is about lift condition. So if the lift is move with constant velocity R so not moving then we can say R= mg here lift is move with some actation A then R1 is greater than the mg so R1 - MG equal to MA so here mg I'm taking that side R1= mg + ma if lift is moving downward direction lift is moving downward direction then mg minus r2 = ma so ma we are taking this side R2 that side then we'll take MG - M = R2 understood or not? So this is very very important. Okay.

[01:00:43]So next one we will discuss about so when the bodies are connected so here you can see I'm taking the two bodies two bodies are attached like this so forces acting on it F m1 and m_sub_2.

[01:01:14]So agillation is in this direction.

[01:01:18]Now anyway contact force will be there between m1 and m2. Right? Contact force will be there between m1 m2. So fdash and here also fdash.

[01:01:31]Is it clear or not? Now you can see here. So aation is moving along this direction. Then force is acting in this direction. So we know f = m a. So here m = what? m1 + m_sub_2 into a f = m1 + m_sub_2 into a is it clear or not? So a = f_sub by m_sub_1 + m_sub_2. So equation 1.

[01:02:03]So reaction force on m1 that is m_sub_1 a = m1 a f by m_sub_1 + m_sub_2. So coming to second equation reaction force on m_sub_2 m_sub_2 a so = m_sub_2 f_sub by m_sub_1 + m_sub_2 equation 3 understood or not? So I hope it is very clear. So now so two bodies are attached. What if three bodies are taken? If I attach three bodies, how it will be? We will see how the contact forces will be there. So everything we will discuss now. Now if two bodies are attached, so I'm taking here You have fun.

[01:03:14]You have fun.

[01:03:28]Okay. Now you can observe we know that f = m a new second law. What is f? m1 + m_sub_2 + m3 into a m1 + m_sub_2 + m3.

[01:03:46]Now you can say a = f by m1 + m_sub_2 + m3. So equation one.

[01:03:55]So reaction force f_sub_1 = f_sub_1 a that is nothing but so contact force you can say contact force contact force between m1 and m_sub_2 between m1 and m2 only between m1 and between m_sub_1 and m_sub_2 between m_sub_1 and m_sub_2.

[01:04:21]Okay. So now we can take So f_sub_1 = m_sub_2 + m_sub_3 f_sub_1 m_sub_2. So m_sub_2 and m_sub_3 a right. So f_sub_1 = m_sub_2 + m_sub_3 into a = f_sub by m_sub_1 + m_sub_2 + m3 equation 2. So now contact force between m_sub_2 and m_sub_3 m_sub_2 and m_sub_3 that is f_sub_2. So f_sub_2 we are going to write for f_sub_2 equation m_sub_3 f_sub by sorry m_sub_3 a we can write okay now I will write here like this so m3 into a equal how much f_sub by m1 + m_sub_2 + m3 so equation three so observe carefully Okay.

[01:05:48]Okay. So I hope observe carefully your diagrams.

[01:05:53]So M1 M2 M3. So contact force between M1 M2 is F_sub_1. Contact force between M2 and M3 is F_sub_2. So F= M A. So M= M1 + M2 + M3 into A. So A= M1 + M2 + M3.

[01:06:12]Understood or not? I hope it is very clear. So between M1 and M2 F_sub_1 = M2 + M3 into A. So A= M1 + M2 + M3. Then we'll get So between M2 M3 that is F_sub_2. So m3 m3 into f by m1 + m_sub_2 plus okay I hope it is very clear. So this is about when bodies are connected right so attached attached now if bodies are connected with the string what happens if the body is placed on inclined plane what happens we'll see so I'm placing the body on inclined plane so here I'm taking like this so I am considering the body is placed here.

[01:07:06]So this is the angle theta understood or not? So weight is acting downward direction. So I'm taking here this the weight is acting downward direction. So, mg cos theta, mg cos theta, here is angle theta and here is mg sin theta and here is the reaction force r.

[01:07:36]So, ailation will be in this direction A.

[01:07:40]Okay. So if it is friction surface, if it is friction surface, friction will be acting opposite of applied force or movement of the body. So body is moving downward direction. Right? Body is moving downward direction. So normal reaction is acting like this. Mg cos theta is balanced by the normal reaction. So here mg sin theta weight is acting downward direction. Here why we are taking r. So here r = mg cos theta. Why we are taking like this? Because the body is moving on the incline plane along the horizontal direction. It's not moving like this, right? Along vertical direction to the plane. Okay. So it is moving along the horizontal surface like to the plane like this. along horizontal on the on the plane on the inclined plane the body is sliding like it is along horizontal direction there is no motion in vertical direction that's why r = mg cos theta r = mg cos theta now you can see here as I mentioned f= ma f= ma newton second law f= ma net external force acting on it is equal to mass of the body and accelation of the body. So here you can see which one is greater mg sin theta is greater. Why?

[01:09:08]Body is moving downward direction. Body is moving downward direction. That's why mg sin theta is greater than the friction. So if it is friction is greater than so friction is more than mg sin theta then but body must be moving for upward direction. Right? Body should move upward direction. If the body is not moving upward direction. So a body is moving downward direction then towards the downward direction force is greater than the friction. Okay. Suppose I'll tell I'll tell one thing. So 10 so this person A and person B person A applying 20 Newton force on the object. Person B is applying 10 Newton on the body. So person A apply 20 Newton. Person B is applying 10 Newton force on the body. So in which direction the body will move towards the boy? The person which is applying 10 Newton on the object. Yes or no? The person who is applying 10 Newton force on the body in that direction the body will move because there is a greater than than the person B the one who is who is applying 5 Newton on the body. So which one is greater? So leave it about 10 Newton 5 Newton. So I'm applying force. The body is moving towards me like a tager.

[01:10:36]Tagafur. Do you know tagafur?

[01:10:38]Okay. So one side 10% another side 10%.

[01:10:42]So they will drag. Okay. The one who is applying more force uh along that direction the second person. So the second team will move.

[01:10:55]But actually in tagafur if you apply some techniques so we may apply this force but we will say the example for tagafura the one who is applying more force towards that direction will move but it's different in the game so techniques and tactics different but finally in which direction the force is greater that side only he will the team another team will move okay so the one who is applying more force only that team only will win that is a game right here also you can observe the force which is greater in the direction only the body the object will slide so here mg sin theta is greater than the friction so that's why mg sin theta mg sin theta - fs = m a so newton second= ma so you have to fill You have to you have to feel it. Yes.

[01:11:57]Newton's second law net external force acting on the body is equal to mass into acceleration. Yes. Greater minus smaller. Always you have to think greater minus smaller. So when you are adding the numbers greater minus smaller 10 - 5 6 - 3 8 - 2 so 50 - 26. So it will be easy. Okay. So instead of writing minus so bigger values sign we will take right here also always you have to think towards the bigger side force only the body will move the force which is acting greater or more uh more than others more than another force in that direction only the force will act the body will move right yes so mg sin theta minus f= ma Now so fs equal to what? fs = mu s into r. What is r? fs = mu into r= mg cos theta. mg cos theta. Understood or not?

[01:13:05]Mg cos theta. Now you can substitute the values here.

[01:13:24]So here we can take mg common. Shall I take mg common in the left hand side?

[01:13:32]Left hand side mg I'm taking common yummy. So here what is common in the left hand side and the right hand side?

[01:13:45]left hand side right hand side both mass is same so I cancel it okay so now a = g sin theta - mu s cos theta cos theta cos theta cos theta understood or not I hope it is very clear observe carefully here is it clear or not so like that like that each and every point you have to analyze. If you analyze each and every point okay then you can able to draw you can able to write the equations easily.

[01:14:27]Okay. I hope it is very clear understood. So coming to the next one.

[01:14:53]money.

[01:15:14]So force T1, T2, T3.

[01:15:29]Okay. So now you can see here M1, M_sub_2, M3. So angulation is in this direction.

[01:15:43]Okay. Okay. Okay. Okay. Okay. Okay.

[01:15:47]Okay. Okay. Okay. Okay. Okay.

[01:15:50]First weight is acting downward direction.

[01:15:56]R3 weight is acting M_sub_2 G M3 G and here R2 here R1 M_sub_2G okay so I hope it is very clear just check once now you can see here so T1 T1 = F_sub_1. F_sub_2 = F_sub_1.

[01:16:30]Now TS2 = M_sub_2 + M_sub_3 into oh F = MA that is F = M1 + M_sub_2 + M3 into A. So A = F by M1 + M_sub_2 + M3.

[01:16:54]understood or not? So we know f= m= m1 m1 + m2 + m3. So a= m1 + m2 + m3. Is it clear or not? So now a I'm taking here ts2. So now tsub2 = m_sub_2 + m_sub_3 into what is a f by m_sub_1 + m_sub_2 + m3. So this is the equation.

[01:17:27]So equation 1 equation 2 what about tension 33?

[01:17:34]T3 = M_sub_3 A that is M_sub_3 into F_sub by M1 + M_sub_2 + M3. So equation three understood or not? I hope it is very clear. Just check once.

[01:17:54]Check once here.

[01:17:58]Is it clear or not? So m1 m_sub_2 m3 t1 = f = m. So here you can see so m1 + m_sub_2 + m3 that is a = m by m1 + m2 + m3 equation 1. Coming to the ts2 so tension ts2 m_sub_2 + m3 into a so towards that side tension is acting actually moving masses we have to take m_sub_2 + m3. So into a a is nothing but m by m1 + m2 + m3. So t3 only mass m3.

[01:18:34]So m3 a m3 m3 by m1 + m2 + m3. So that is equation three. So is it clear or not? Yes or no. So if you like the content, if you like the channel, do like, share and subscribe to student brand.

[01:18:50]Student brand, right? Yes. Coming to the next one.

[01:19:07]So now pulley mass system. So now you tell me the equation. So I'll give an incident. So now you tell me the now you tell me the equation. Right? So I'm taking this case like this.

[01:19:25]So pulley mass system.

[01:19:31]So here I'm taking here pulley.

[01:19:35]Pulley here this is m1 weightight is acting downward direction.

[01:19:40]M1 g act aulation is there tension will be t1. So here tension t only anyway same thread. So t I'm taking m_sub_2 m_sub_2 g. So here weight is so here condition is very important condition is very important m_sub_1 is greater than m_sub_2 so body is moving downward direction so m_sub_2 will be going upward direction as I mentioned f= ma f= ma so you have to keep in mind when you are writing the equation okay for pulley mass system or constraint bodies are like that If you take anything okay so inclined plane so attached attached to the string okay are connected like that anything if you take okay so F= M so this must be in mind so net external force equal to mass into acceleration so acceleration is downward direction because M1 is greater than M_sub_2 okay so M1 is moving downward direction M2 is moving upward direction now write the equation now write the equation so So write the equation. So for m1 so m1 for m1 = m1 g - t = m1 a. So equation one as I said you have to write the equation right as I said. So weight is m1g is greater than the tension because body is moving downward direction. So aellation is towards weight of an object. Okay. So that's why m1 g minus t = m1 a coming for m_sub_2 for body m_sub_2. So here tension is greater tension is greater than weight of the object. That's why body is moving upward direction. So what is net external force t minus t minus m_sub_2 g = m_sub_2 a. So this is equation 2.

[01:21:51]So how to solve these two equations?

[01:21:53]Just simply add 1 + 2. That's enough.

[01:21:56]Nothing else.

[01:21:58]m1 g - t plus c. Okay.

[01:22:04]T - m_sub_2 g = m1 a + m_sub_2.

[01:22:11]So tdt get cancel g. I'm taking m1 - m_sub_2 = a m1 + m_sub_2. So aation a = m1 - m_sub_2 into g by m1 + m_sub_2.

[01:22:30]So aation you got automatically you can able to identify the tension right.

[01:22:37]Okay. So if you know the aellation if you know the aellation we can find out the tension. If you substitute in equation one, you'll get tension easily, right?

[01:22:48]So not that tension here, tension in the string.

[01:22:54]Okay. So just check once. Is it clear or not? So coming to the next one, one more case. One more case. I'll do it.

[01:23:08]Writing equation is writing equations.

[01:23:12]So for a body a body m1 and m2 that is very important. You must write the equations.

[01:23:21]If you write the equations that's enough. If you take proper notations, okay, simple thing very very very very simple one is keep in mind F= to MA greater minus smaller that's enough LHS side greater minus smaller in RHS side always MA so if you taking M1 M1 A if you taking M2 M2 if you're taking M3 M3 if you're taking M1 plus M2 Okay. So m is mass of the body. On that body what are the forces are acting? So on the particular body greater minus smaller you have to take. So generally bodies okay. So in which direction the force is acting along that direction body will move. It's in the another direction will another direction the body will not move. If you are taking horizontal direction only the body will move along horizontal direction at a time it won't move horizontal as well as vertical right okay maybe different cases but here maximum the bodies will move along horizontal so according to the position like if you take the on the ground so like a police different cases so the point is the ultimate point is so towards the greater force side the body will move that's enough that is the end of the story okay so no need to no need to give introduction and highlighting so giving a background music after that elevation after that uh interval after that again story continues at the end so elevation and end of the story no not like that greater minus smaller that's enough greater minus smaller equal to m into a that's enough.

[01:25:22]Okay. So, so one more.

[01:25:32]So, I'm taking here object.

[01:25:46]So m1 m_sub_2 so bodies are moving aation a. So here aation here tension t m1g okay so tension t here understood or not now you tell me so which one is greater m1g greater m1 g minus t = m1 a so that is equation one coming to equation 2 t = m_sub_2 a so equation two substitute in t value m1 m1 gus m_sub_2 a = m1 a so simply we can say from equation 1 and 2 1 and two so t I'm substituting in equation one equation two in equation one now take that side so m1 g = m1 + m_sub_2 into a a = m1 g y m1 plus m_sub_2. So equation one then if you substitute here tension you'll get right. So tension t = m1 m_sub_2 g by m1 + m_sub_2 equation 2.

[01:27:08]So like that that's enough simple understood or not? So very easy try to identify then you'll get the equation.

[01:27:20]Is it clear or not?

[01:27:23]Yes. Coming to the same case, we can take the friction.

[01:27:36]So one example I'll give you can do it and uh let me know. So here friction surface fs = mu into fs = m into mg that is uh here here I'm taking m_sub_2g m_sub_2g m_sub_2 g r so m equal to m_sub_2g now you can write the equations so I hope it is very clear are you understanding or not just you can take and write the equations and let me know.

[01:28:13]Okay. So in the next class in the coming class so if you know just practice this question that's so if you like the content do like share and subscribe to student the brand. So yes few more examples I can give but uh try this one we'll see. Thank you so much for joining and attending listening. If you like the content if you like the channel do like share and subscribe to student the brand. So we'll come with the different topics in the coming class and every day in the morning live class will be there around at 8:00 8:00 a.m. So in the evening time also 8:00 p.m. okay live classes will be there. So topic and class I will update in the community post. You can check in the community post each and every time whenever I'm updating. Okay. So I will release that. Okay. So what we can say date and timings and everything like a poster. So thank you so much for joining and attending listening and giving an opportunity to teach. This is signing off. Do like, share and subscribe to student brand if you like the content.

[01:29:21]If you like the channel so share to your friends, ask subscribe friends to join to the class. So spread one word regarding the channel. So drop one word among your friends regarding the channel. Share to everyone. So one share gives lot of energy to me. One like gives so uh to help so many students so so many people right so by in your hand so it will be in your hand only just click and share to your friends so let them know let them know regarding the channel uh let them know regarding the concept let them know regarding our live class let them know regarding the channel so thank you so much we'll see you in the next class thank Who?