# Donkey for a cart and the carrot for a magnet

Atilla1982
Me and my buddy had a discussion the other day.
Imagine the scenario with the donkey that has a danglin carrot in front of him. If we swap the donkey for a cart and the carrot for a magnet, what would happen?
My buddy was pretty sure that the cart would move, and I thought that it wouldn't. So who is right?

whozum
If the conditions were such that the two objects were magnetically attracted, they would not move (roll) if the magnet is rigidly attached to the cart by some kind of overhang. If the magnet is not attached to the cart in any way then there will be some attraction.

Atilla1982
yeah, there would be an overhang. The magnet and cart would be one, but there's a gap between them. My friend is still convinced that the cart will roll anyway. Can anyone please explain why it won' t ?

ascky
What the cart is made of is important, as to whether you get paramagnetic or ferromagnetic effects.

It depends whether you mean 'will the cart will move', or 'will there be a magnetic force'. Also remember there will always be very weak diamagnetic effects, because all substances are diamagnetic.

If you're talking about a four-wheeled horse of Troy to substitute for your donkey, and a carrot-shaped magnet, the cart won't move. But if the cart is an iron Matchbox car, and your magnet is very strong, it will...

ascky
If the magnet and cart are rigidly attached, then there's something holding them apart. So all that will happen is the stuff between the magnet and the cart will get squashed. If it's rigid, it can't get squashed. So nothing moves.

ascky
If it were true that you could get something to move as your friend proposes, you could weld a magnet on a stick to your car, and you wouldn't need an engine.

Staff Emeritus