I mean, I always used to fancy as a kid why can’t we use magnets to keep a fan going in circles? Why can”t we create a perpetual machine using magnets? Even if the magnets get worn out, we can still use them for considerable time. What is the science behind it that makes it impossible?
In: Engineering
You can use gravity to move stuff. If you like, you can push a cart full of bricks up to the top of a hill. Then you can attach a rope to the cart, and let the cart roll back down, and it’ll pull on the rope. You can use that to do work.
But what you *can’t* ever do, is get more work out of the cart rolling down the hill, than you spent on pushing it up the hill. Every downhill movement of the cart, must be paid for, sooner or later, with an equal uphill movement. There’s no shortcut you can take from the bottom of the hill to the top, without spending energy to get there.
The same thing is true with magnets. You can push the repelling poles of two magnets together if you like, and then if you release them, the repulsive force will make them move away from each other. But just like the cart on the hill, that repulsive movement will never give you back more energy than you spent on pushing them together in the first place. And the same is true if you use attractive force instead of repulsion. Every bit of energy you get from allowing the magnets to push/pull on each other, must be paid for by spending energy on pushing them together/pulling them apart, to get them into that position.
TL;DR: Magnetic forces can store potential energy, but they can’t give you energy for free.
(edit: removed a paragraph about a math topic called “conservative fields,” because some details were potentially misleading/not correct in the most technical sense.)
Latest Answers