Help With Science Fair; Calculating Force

  • #26
Simon Bridge
Science Advisor
Homework Helper
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Though what I don't understand is, if a pulley reduces the force necessary to lift an object by half, if you use enough pulleys, wouldn't you be able to reduce the force necessary to reset the weight to a level that the generator could achieve by itself?
Yes - it would reduce the force. But it still takes the same amount of energy - at best.

If you reduced the needed force by a half, then it would take twice as long to reset (strictly: you have to haul in twice as much rope).
And that is with magic lossless pulleys - each pulley will add an extra loss to the system so less of the applied power goes into resetting the system.

Have you seen:
http://www.lhup.edu/~dsimanek/museum/unwork.htm
... it's a good place to learn about these kinds of traps.
 
  • #27
tms
644
17
It isn't a question of force, but of energy. Raising an object to a certain height takes a certain amount of energy (at least), regardless of how you do it.

In addition to that, each pulley loses energy to friction, and the more pulleys you have the more friction there is. Plus, since the pulley have mass, they require energy to spin.

There ain't no such thing as a free lunch.
 
  • #28
OmCheeto
Gold Member
2,131
2,581
The closest I can come to a ready made device is a pair of lockwire pliers:

https://www.youtube.com/watch?v=CU-NAX7vwfY

If your experiment fails to perform as expected, you will at least have something you can nicely twist wires with.
 

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