If you lean a stick against a wall, the stick is applying force to the wall. Possibly for hours, days, or even many many years. Does that mean the stick is generating infinite energy?
No, Pliny, it does not. And as usual the problem here is that you just don't understand what you're talking about.
You're expending energy by pressing against the wall-- contracting your muscles uses chemical energy, and generates heat. But you're not generating energy any more than the stick leaning against the wall is generating energy.
Why would I think the stick is generating infinite energy in such case? The force of gravity is the only thing in play here keeping things in an equilibrium. Now if the stick were off the ground, just sort of up against the wall, seemingly defying gravity, I would wonder how that could be. If there were no mass holding it up on the wall there would have to be some force holding it up.
And holding the ball at constant height is no different from a table holding a ball at constant height. Is the table burning energy? If a ball sits on a table for 100 years, does that mean that the table has generated an incalculable amount of energy during that time? No.
All you are doing in this instance is inserting a mass so energy does not need to be expended.
If I hold my arms out in front of me it takes energy for me to hold them there. If I put a table underneath them they are at rest and I no longer need to expend any energy holding them up.
If you say so.
If you put a brick between two magnets to keep them apart, is the brick generating energy? Nope.
Right. A mass is keeping them apart. The same as a table keeps things from falling on the floor. There is no energy necessary to hold them up in that case and in your case there is no energy necessary to keep the magnets apart.
Your muscles are burning chemical energy while you're holding the magnets in place, but that energy isn't being added to the system of magnets. It's being lost as heat. It's not being added to the system of the magnets.
So all my muscles are doing are burning chemical energy and producing heat? There is no work being done.
With one hand on each magnet, the magnets when brought into proximity to each other will pull my hands together. Is there any energy used to do that? Usually my muscles have to burn some chemicals and produce some heat to bring my hands together.
Edited by Pliny, 29 October 2011 - 07:30 AM.