Feynman Lectures vol.1 Chapter 4 Topic 4-2GravitationalPotentialEnergy

• Rishabh Narula
In summary, the author is explaining the first law of thermodynamics in detail and how it applies to weight lifting machines. He provides an example of how to lift a weight using a weightlifting machine and explains that the gravitational potential energy of the weights remains constant.
Rishabh Narula
Could anyone explain me in simple words what is being said in this topic from this book (great book and author btw)...
i don't understand after it starts talking about perpetual motion and lifting and lowering of weights.please explain in simple words.
okay someone said to add more details to my question since it wasn't clear what i was asking.
so i got confused at this point-
"Consider weight-lifting machines—machines which have the property that
they lift one weight by lowering another. Let us also make a hypothesis: that
there is no such thing as perpetual motion with these weight-lifting machines. (In
fact, that there is no perpetual motion at all is a general statement of the law of
conservation of energy.) We must be careful to define perpetual motion. First,
let us do it for weight-lifting machines. If, when we have lifted and lowered a lot
of weights and restored the machine to the original condition, we find that the
net result is to have lifted a weight, then we have a perpetual motion machine
because we can use that lifted weight to run something else."
umm like how exactly weight lifting machine lift one weight by lowering another.and what does that line mean that no perpetual motion at all is a general statement of the law of conservation of energy.im also confused by the last four lines and the whole topic that follows...can't seem to visualize what is being said...so if anyone can say the whole thing in this topic in simpler words or help me visualize it would be of great help.

im also a bit more confused by the next para-

"
A very simple weight-lifting machine is shown in Fig. 4-1. This machine lifts
weights three units “strong.” We place three units on one balance pan, and one
unit on the other. However, in order to get it actually to work, we must lift a
little weight off the left pan. On the other hand, we could lift a one-unit weight
by lowering the three-unit weight, if we cheat a little by lifting a little weight
off the other pan. Of course, we realize that with any actual lifting machine, we
must add a little extra to get it to run. This we disregard, temporarily. Ideal
machines, although they do not exist, do not require anything extra. A machine
that we actually use can be, in a sense, almost reversible: that is, if it will lift
the weight of three by lowering a weight of one, then it will also lift nearly the
weight of one the same amount by lowering the weight of three. "

why would you need to lift a little weight off the left pan?wouldn't the machine lift the right side(with one unit) up as soon as you placed 3 units on the left side?also what does the last four lines here mean again?how will you lift a weight of 3 by lowering a weight of one?how can one weight on one side make 3 weights on the other side go up?

Last edited:
What is precisely your question? I consider Feynman's Lectures some of the best-written textbooks. So I don't know, how to reformulate it in "simple words".

vanhees71 said:
What is precisely your question? I consider Feynman's Lectures some of the best-written textbooks. So I don't know, how to reformulate it in "simple words".

Rishabh Narula said:

You can't copy just that. He explained a bit more in detailed in several paragraphs following that, even in the form of an example.

http://www.feynmanlectures.caltech.edu/I_04.html
Zz.

Rishabh Narula said:
how exactly weight lifting machine lift one weight by lowering another
A lever allows you to lift one weight by lowering another. Similarly with a pulley, if you attach two weights by a pulley then lowering one weight can lift the other.

Rishabh Narula
Dale said:
A lever allows you to lift one weight by lowering another. Similarly with a pulley, if you attach two weights by a pulley then lowering one weight can lift the other.
okay thanks that solves atleast one doubt here.

Hey can someone please answer the questions i asked...im still pretty confused with this whole thing...i can move on but if someone could answer them straight forward it would be great. :3

okay so i read more and i think i get the gist now...that weight of balls times height lifted or lowered remains constant i.e the gravitational potential energy...right,right? anyways moving forward now... :3

1. What is gravitational potential energy?

Gravitational potential energy is the energy that an object possesses due to its position in a gravitational field. It is the potential for an object to gain kinetic energy as it falls towards a larger object, such as the Earth.

2. How is gravitational potential energy calculated?

The formula for calculating gravitational potential energy is GPE = mgh, where m is the mass of the object, g is the acceleration due to gravity, and h is the height of the object above the ground or reference point.

3. What is the relationship between gravitational potential energy and mass?

The gravitational potential energy of an object is directly proportional to its mass. This means that as the mass of an object increases, so does its gravitational potential energy.

4. How does the distance between two objects affect gravitational potential energy?

The gravitational potential energy between two objects is inversely proportional to the distance between them. This means that as the distance between two objects increases, the gravitational potential energy decreases.

5. Can gravitational potential energy be converted into other forms of energy?

Yes, gravitational potential energy can be converted into other forms of energy, such as kinetic energy. When an object falls towards a larger object, its gravitational potential energy decreases while its kinetic energy increases.

• Mechanics
Replies
11
Views
3K
• Mechanics
Replies
35
Views
4K
• Classical Physics
Replies
5
Views
4K
• Mechanics
Replies
2
Views
2K
• Mechanics
Replies
4
Views
9K
• Mechanics
Replies
11
Views
1K
• Other Physics Topics
Replies
2
Views
2K
• Mechanics
Replies
4
Views
6K
• Other Physics Topics
Replies
7
Views
4K
• Classical Physics
Replies
3
Views
2K