8.01x - Lect 11 - Work, Kinetic & Potential Energy, Gravitation, Conservative Forces
Why Physics Stack Exchange recommends it
Physics Stack Exchange askers cite it as the source of confusing points about work done by gravity versus the lifting force and about energy conservation in the loop-the-loop problem.
Recommended by 1 people across 1 different months, 2023 to 2024.
What it is
Walter Lewin's MIT 8.01 lecture on classical mechanics covering work, kinetic energy, potential energy, Newton's law of universal gravitation and conservative forces. It is a blackboard lecture with live demonstrations, including the loop-the-loop problem.
What people said
Recommends Khushiv Batra · 2024-07 · Physics Stack Exchange · on “Why is work done by force $+mgh$ in the situation of throwing something up?”
If there is a particle at point A(at rest) and a force moves it to point B(Above point A vertically)(final velocity = 0 at this point), the work done by gravity is $-mgh$ . This I understand as the force of $mg$ is downwards while displacement is upwards so negative work is done. But the work done by the force that brings it above to point B is $+mgh$ . I dont think its necessary. That will mean that the force making it move up is $+mg$ but it can also be something else. This is the part that I do not get. Maybe its very simple and I am not getting the concept. Can somebody explain why is that both intuitively and by theory? refer to [this video] at 5:40
Cites MrBrN197 · 2023-04 · Physics Stack Exchange · on “How is Potential Energy equivalent to Kinetic energy in the loop the loop problem?”
I'm watching a Physics MIT lecture about classical mechanics and I'm on the episode about Work and Energy. I'm stuck at this point in the video [this video] . because I can't wrap my head around how the solution the lecturer uses is valid. basically, how is it in the "loop the loop" problem that the potential energy is related to the kinetic energy? at the beginning of the lecture, he starts by deriving 1/2mv^2 using the definition that this work done is defined as the integral, with respect to dx of a force where the force acts along that distance dx. so this comes out to being 1/2mv^2 but the velocity (v) must also be in the direction of the force. In the "loop the loop" problem the velocity v
Cites Erick Hernandez · 2024-01 · Physics Stack Exchange · on “Why is the work done by moving an object up vertically not greater than mgh”
Watching Walter Lewin's classical mechanics. In lecture 11 [this video] he says when moving object up vertically distance h, the work done by gravity is -mgh, which makes sense. But then he said the work done by him is obviously mgh. Why is that the case? Doesn't the force he exerts need to be greater than mg in order to overcome the force of gravity? I.e. I would expect the work done by him to be (mg+ma)h. Thank you for your help.