- #1

Rishabh Narula

- 61

- 5

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?

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?

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