So if I push against a wall and neither the wall nor I move any distance then no energy has been expended, although I might break out into a sweat.
That's a mathematical formula for determining the amount of energy expended to move an object a specified distance. If the distance is zero of course mathematically I get an answer of zero. I may apply a force but not enough to overcome the inertia of the mass. Does that mean zero energy has been expended?
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.
But in fact, a magnet on a fridge does not drop to the floor. The force of gravity, is pulling it's mass toward the floor. The properties of the magnet are keeping it stationary resisting the pull of gravity. In effect, it is similar to me holding a ball outward in my hand, I am expending energy by preventing the ball from dropping. When I run out of energy and can no longer hold the ball it drops to the ground.
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.
Essentially, a state of equilibrium of forces is attempted to be achieved by all objects, it takes energy to maintain them in a state out of equilibrium.
All objects on Earth to reach equilibrium remain on the ground. An energy is applied to move it off the ground
and it must be continuously applied to keep it off the ground in a state out of equilibrium.
The magnet behaves as any other object that is put on a vertical surface. It falls off, unless it is in contact with a ferrous metal, in which case it does not.
The formula tells me no energy is being expended. The magnet is moving 0 distance. Is this the case?
If I have two magnets and hold them apart, keeping their polar opposites from moving toward each other. I must use force. How long I can apply the force to keep them apart is the amount of energy I have to keep them apart. I don't see how that energy can be zero???
If you put a brick between two magnets to keep them apart, is the brick generating energy? Nope.
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.
Edited by kimmy, 27 October 2011 - 11:12 PM.