How much does a falling magnet weight?


The same weight. Easy as that, but when you see the experiment in which a magnet falls through an aluminium pipe and it slows down you wonder what the heck is happening there. If the magnet slows down doesn’t that mean that it will weight less? Or not?

Well, you got to know one thing: the magnet will weight the same, but it will slow down due to the electromagnetic interaction between the falling magnet and the aluminium pipe.

Andy, from The royal Institution explains what happens: when the magnet falls it generates an electric current in the pipe. That electric current, in turn, generates a magnetic field that traps the magnet in it slowing it down. Brilliant.

Note: electric charges that move generate a magnetic field and a magnet that moves generates an electric field. This is why both forces are part of the electromagnetic field. Sweet.

Basically, if you measure the system composed of the pipe + the falling magnet you’ll get the same weight as for both combined, if you were to weight them with a scale separately. While the magnet falls, the gravity is countered by the electromagnetic force and thus the system weights the same. It is like you give that magnet to someone to move it from a higher point to a lower point.

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