# Feynman irreversible and reversible weightlifting machine

Est120
Homework Statement:
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.
Relevant Equations:
understand what feynman says
i have tried to understand Feynman's words i think i finally understands what he means by "we must add a little extra to get it to run"
he refers to the "inversion" of the process, that's when we need to add extra work (lifting up a little mass)
please correct me if I am wrong, this is something i want to have clear in my head

Staff Emeritus