8.01x - Module 14.04 - Conservative and Non Conservative Forces.

[@smylegalaxy2810]

dear sir. You are like an angel for all students who want to learn physics.

[@matthewjames7513]

4:38 small typo. There should be an integral in front of F . dl

[@naman881]

Thanks professor. I am only getting marks by knowing the Defination of conservative and non conservative forces, but I knew that my concept was not clear. Now I got a clear concept

[@ashokbharati6710]

Sir... You are a LEGEND🔥❤️

[@Feynman_Fries]

Hi Prof Lewin. Thank you for all the amazing work you have done over the years, I use so much of what I have learnt from your videos during my physics classes to fascinate students like you did. While I was working with Work, I came across a problem that has been bothering me so much and I haven't been able to find out what's wrong there. Here is my confusion: when we determine work done by friction down a ramp (of a constant angle like an inclined plane or a varying angle like a curving ramp), we find that the work comes out to depend on the "horizontal length" of the ramp and not the length of the ramp itself (-umgx, where x = horizontal length of the rough ramp). In such a scenario, when work by friction seems to be path independent, how do we justify it as a non conservative force? Kindly help!

[@AmitMishra-qs5ru]

well i think that the frictonal force was dependent on the inclination as kmgcos(x) not the displacement which is still the total rough surface

[@yukikomatsu2447]

When I move an object from point a to point b, I do positive work and the friction does negative work, so the total work done is zero. Then where does the energy of heat or sound come from? If I move an object away from the earth and stop somewhere in the universe, I do positive work and the gravity does negative work, so again the total work done is zero. In this case, is heat produced?

[@manujasan9176]

I think of it like this, when you move an object from a to b applying just enough work to compensate the friction, it has to move with constant velocity. So if you look at the object from a frame of reference where only the object is visible and not any of the surroundings, you will see it moving with constant velocity, hence it would appear as theres no external force acting on the object. But if you look it from a reference with the surroundings, without the positive work it looses it's kinetic energy as heat and sound hence gradually slowing down the object (friction) and you have to apply just enough work to compensate the loss of energy to maintain the velocity(positive work). Speaking of gravity, if you move an object away from the earth, theres no loss in heat and sound(assuming it's moving through vaccum otherwise there would be friction and it won't be conservative) . Instead, the work you do to compensate for the attractive force is stored as potential energy of the system (the object and the earth here) . So if you stop the object at somewhere in the universe, it will use the potential energy to gain velocity to move towards the earth.

[@palneema5939]

Professor, can you explain the meaning of this sentence that- A particle moving one dimensionlly in conservative field may have more than one turning points

[@lecturesbywalterlewin.they9259]

>>>A particle moving one dimensionlly in conservative field may have more than one turning points>>> bizarre statement but not incorrect. A mass oscillating on a spring is a 1D motion with many turning points

[@arjunsagar6403]

great explanation, professor

[@lecturesbywalterlewin.they9259]

Glad you liked it!

[@prafullakalita1378]

Sir, what electromagnetic wave actually is ? How does it propagate ?

[@lecturesbywalterlewin.they9259]

watch my 8.02 lectures - it's all there

[@InventTwig]

2:16 professor you said that 'in' Newtonian mechanics gravity is a conservative force , so is gravity non conservative in general relativity or elsewhere?

[@lecturesbywalterlewin.they9259]

gravity is always a conservative force. The work done by gravity in moving a mass from A to B is independent of the routing.

[@InventTwig]

Thank you professor !

[@pordebaixodabandeira]

here's a silly question, i get the conservative and non conservatives forces, but my question is : the work of Walter Lewin shouldnt be higher than the work of the frictional force? my thought is : since the thing is moving, the force that u apply when it's resting is at least slighly higher than the friction force and during the path they could be equal so they will cancel out and it will go in uniform motion, so as the force in the beginning has to be a bit higher than the static friction shouldnt the work(WL) be a little bit higher than the work of friction? or you are just saying that they are equal because the difference of the forces in the very beggining is negligible?

[@lecturesbywalterlewin.they9259]

If I push an object on my table from A to B I have to overcome the friction. I do positive work W, friction does negative work W. the net work is ZERO as I start with zero speed at A and end with zero speed at B.

[@pjyt]

At several points during the motion, the force of the professor on the wallet is more than or equal to or less than the force of friction from the surface. Breaking down the overall motion into infinitesimal displacements and calculating the works done by these forces and adding all such works -> is is possible to show that the total work done is equal to the ultimate change in the kinetic energy of the wallet. Since the wallet was at rest at A and is also at rest at B, it is said that the works done by the professor and the surface friction are equal in magnitude and opposite in sign.

[@afsawafsaw1715]

Sir can you please explain That conservative force is negative gradiant of potential energy

[@lecturesbywalterlewin.they9259]

I cover that in my lectures - watch them!

[@afsawafsaw1715]

@@lecturesbywalterlewin.they9259 thank you sir .

[@luxtenebris764]

@@afsawafsaw1715 which lecture ?

[@swapnilsrivastava1378]

Professor in work done by "WALTER LEWIN sir",,,,the frictional force is still is π radians to the motion of the particle,,,,so how the WD was positive!!! I think there was supposed to be WD by the force applied by you on the particle!!! I Respect you a lot sir from 🇮🇳

[@lecturesbywalterlewin.they9259]

you have to overcome the frictional force thus your force is in the direction that you move an object thus you do positive work