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

Added: 2026-05-19

[00:03:44]Hello students.

[00:03:47]Hello. Hi students. Welcome to the student brand. This is today topic is loss of motion. Loss of motion.

[00:03:56]Right. So in this topic we'll talk about inertia.

[00:04:11]momentum, impulse, Newton's last after that weight, friction, after that connected bodies.

[00:04:27]Okay.

[00:04:29]So after that we'll discuss puly mass system and few free body diagram analysis.

[00:04:38]Right. So let's discuss about inertia.

[00:04:46]So I'll tell few examples then you'll get to know.

[00:04:51]I'll tell few examples.

[00:04:55]So the body is so a book is placed on the table.

[00:05:00]Point number one.

[00:05:03]And the second one is if you hit the carum coins, the bottom carum coin will move forward. Remaining coins will stay in the same stitch.

[00:05:16]And one more example. Take a glass of water, place the paper over it. And take a coin and place over it. And pull the paper. The coin will fall for in the same direction. In the same place, coin will fall down.

[00:05:32]And if you shake the branches of the tree, the fruits will fall down.

[00:05:39]And if you beat carpet with stick, if you beat the carpet with stick, the dust particles will comes out and fall. The carpet will move.

[00:05:55]The carpet comes under motion.

[00:06:02]And one more example.

[00:06:05]So when you switch on the fan, it continuously rotating.

[00:06:10]Once you stop the fan, still the fan continues its motion until certain time.

[00:06:19]After that only it stopped.

[00:06:23]After that only it will stop.

[00:06:28]And one more example when the person is getting down from the running bus so he has to move forward in the same direction otherwise he'll fall and roll.

[00:06:41]Okay. And an athlete long jump person so he has to go little backward has to run some far distance.

[00:06:56]Not too much for but certain appreciable distance.

[00:07:04]He has to run certain distance then he will take a long jump.

[00:07:11]So by that you will get that momentum then it continues right. And one more example you are in the bus.

[00:07:23]So in the moving bus suddenly the driver applies brakes we feel we fall forward.

[00:07:33]We are not only feeling we we will fall forward.

[00:07:38]Why?

[00:07:40]And one more example when you uh standing in the bus then the bus suddenly start we fall backward.

[00:07:53]So you can observe all these examples.

[00:07:57]There are many examples out there. If you observe all these examples, okay, one common point is inertia.

[00:08:07]Maybe there are types I can agree. But one common point is that is inertia.

[00:08:15]So inertia is nothing but so inability of the body to change its state of change its state or the body is unable to change its state without external force.

[00:08:34]If external force is applied on it then the body trying to change its position change its state.

[00:08:43]without external force acting on the body. Unless external force acting on the body, the body does not change its state. So here types are there inertia of rest, inertia of motion, inertia of direction, inertia of rest, inertia of motion, inertia of direction. So what is inertia of rest?

[00:09:10]So best example if you hit the coin so the coins will fall say fall fall in the same place.

[00:09:19]Okay. So the bottom coin will move move forward.

[00:09:25]And one more example.

[00:09:28]If you shake the branches of the tree, the branches of the tree comes under motion. The tree the fruits will fall the fruits will fall down.

[00:09:40]The fruits will fall down due to inertia of rest. If you beat the carpet with stick the dust particles comes out, the dust particles will fall down due to inertia of rest.

[00:09:56]And coming to inertia motion when you when you switch off the fan still the fan continues its motion after certain time it stops and inertia of direction if you take a stone and w like this and leave along the tuition direction the stone will move.

[00:10:21]So you can see in the winter season so when you are cycling a bicycle so the water droplet moves along the tangential direction.

[00:10:35]Okay. So these are all we can say inertia of rest motion direction and even a ball is moving on the ground unless external force acting on it we can't able to change the direction direction of the ball okay so that these are all examples these are all examples we can say energy of rest inertia of motion energy of direction so we are Talk about loss of motion.

[00:11:09]Loss of motion.

[00:11:18]Loss of motion. Right?

[00:11:23]Yes.

[00:11:25]So, next one is momentum.

[00:11:28]Momentum is nothing but mass into velocity.

[00:11:33]So we are talking about inertia of rest inertia three times inertia.

[00:11:48]First one is rest.

[00:11:51]Second one is motion and third one is direction.

[00:12:02]understood or not?

[00:12:04]So I hope it is very clear. Now we'll discuss momentum.

[00:12:13]Momentum equal to mass into velocity.

[00:12:18]Momentum equal to P bar = M into V bar.

[00:12:24]kg m/ second.

[00:12:30]Okay.

[00:12:31]And here conversation of momentum momentum before collision equal to momentum after collision. m1 u1 + m_sub_2 u2 = m1 v1 + m_sub_2 v_sub_2.

[00:12:45]Okay. So here so conversation of linear moment here m1 u1. So after collision m_sub_2 u2 after collision you can see m_sub_1 v_sub_1 m_sub_2 v_sub_2. So the bodies are moving with the m1 v_sub_1 collision.

[00:13:14]So m1 v_sub_1 m_sub_2 v_sub_2.

[00:13:20]Now you can see m_sub_1 u1 + m_sub_2 u2 = m1 v1 + m_sub_2 v_sub_2.

[00:13:33]Okay. So even kinetic energy also we can take of m_sub_1 u1² + of m_sub_2 u2² = of m_sub_1 v1² + m_sub_2 v2² okay so momentum momentum before collision equal to momentum after collision So I hope it is very clear understood or not?

[00:14:09]Yes. So next one, next one we will discuss about impulse impulse.

[00:14:36]impulse.

[00:14:43]So impulse I = F into T.

[00:14:49]Hi ma welcome to the class. I = F into T.

[00:14:55]So that is impulse equal to change in momentum m_sub_1 minus mu final momentum minus initial momentum.

[00:15:05]So moment already we know that mass into velocity.

[00:15:13]Okay. So I hope it is very clear right.

[00:15:19]So next one we'll discuss about Newton's first law, second law, third law.

[00:15:27]So Newton's Newton's first law first, second law and third one is third law.

[00:15:45]So what is first law? Notice first law describes inertia.

[00:15:52]Okay. So mass is measure of inertia.

[00:15:56]And coming to the second law, the net external force is equal to mass into acceleration or the rate of change in momentum.

[00:16:13]Rate of change in moment of the net external force net external force.

[00:16:28]Here you can see FXL equal to rate of change in momentum. FB - M U by T is directly proportional to then FX = K into MB - M U by T MB minus M U by T understood or not? So now fra = So k = 1 then m you're taking v minus u by t then fal = mass into acceleration net force acting on the body is equal to mass into acceleration mass into acceleration. And I hope it is very clear understood or not.

[00:17:30]Okay.

[00:17:32]So next one.

[00:17:51]Next one we are talking about Next one.

[00:18:14]So there's a proportionality constant.

[00:18:17]So in S system any system K = 1 only we will consider.

[00:18:24]And here next one we will discuss about friction.

[00:18:32]So friction friction is nothing but which opposes the applied force acting on it which opposes the applied force acting on the body. So there are static friction static friction.

[00:18:58]Second one is limiting friction.

[00:19:04]Limiting friction.

[00:19:07]And coming to third one kinetic friction.

[00:19:16]Kinetic friction. In kinetic friction one is sliding friction and the base rolling friction.

[00:19:28]sliding friction and rolling friction static friction. So when the body is placed on the table so force is acting so fs F static friction will be acting opposite.

[00:19:47]So when the body is ready to move this the maximum static friction maximum value of static friction that is limiting friction the body is ready to slide ready to move.

[00:20:00]Okay. So coming to the chinetic friction. So you can see so one body slide so another. So like you can see the example uh windows.

[00:20:13]Okay. one uh window will slide over another right you can see that in a fixed one and coming to that rolling friction anyway so you can see daily are observing the bodies are rolling like a luggage bag everything now if you draw the graph now if you draw the graph so we'll see that So I'm drawing the graph. Observe here carefully.

[00:20:57]So friction applied force.

[00:21:08]So mag the static friction.

[00:21:12]So this the maxal of static friction and ready to so anyway it is moving here sliding kinetic friction here fs = mu into r here fk = muk into r static friction static friction max value of static friction maximum value of static friction and here kinetic friction.

[00:21:53]Kinetic friction.

[00:21:55]Okay. Here limiting friction.

[00:22:02]Limiting friction.

[00:22:05]Understood or not? So I hope it is very clear.

[00:22:08]So this is the graph related to applied force and friction.

[00:22:15]Okay. So it is the maximum value of static friction. There the body is ready to slide.

[00:22:22]So once it is start moving it is comes under kinetic friction.

[00:22:28]Okay. So until from here to here is static friction.

[00:22:33]Okay. So apply force on x-axis friction on yaxis.

[00:22:38]So next one we can see weight.

[00:22:52]So when the body is in lift, so I'm taking the body is in lift.

[00:23:02]So reaction force is upward and weight is acting downward direction. Even on the table also weight is acting downward direction action will be upward direction. So the body is move with a constant velocity if it is not moving r = mg.

[00:23:23]And the next one if the wedg is if the lift is moving upward direction R1 M1 R1 here I'm taking MG lift is moving upward direction if the lift is moving upward direction R1 minus MG = M A so R1 = MG + M A so equation one.

[00:23:54]If the lift is moving downward direction, lift is moving downward direction mg and R2.

[00:24:06]So, lift is moving downward direction.

[00:24:12]Okay. So, mg - r2 = ma.

[00:24:18]So mg - m a = r2 understood or not one check here.

[00:24:41]Is it clear?

[00:24:50]Next one.