Falling Magnets

Watch the magnets dance in a pattern as you spin a large disc and set them in motion. Magnetic repulsion and eddy current braking create curving patterns.

Explanation

There are a few forces at work in this disk.

When you spin the disk quickly, the magnets fly out to the edge of this disk. The rim forces them to take a curved path.

Any force that keeps an object going in a curved path is a centripetal force (a centre-seeking force). Wet clothes in a washing machine are held in a centripetal force by the walls of the machine, while the water in the clothes is not. The water escapes through the holes in the walls.

When you stop spinning the disk, gravity’s force works on the magnets to pull them down. But they don’t fall down quickly as you might expect.

When a magnet is moved near a conductor such as the metal that makes up the circular disk, small rings of electrical current form in the metal. Those rings of electricity are called eddy currents.

Magnetic fields surround eddy currents and repel any magnets that come near them. This causes the magnets to fall slowly.

When the magnets are close enough to each other, they begin to repel each other, so appear to float on top of each other.

Extras for Experts

A magnetic field comes about because the atoms inside a magnet contain unpaired electrons that are all oriented the same way. This orientation is known as an electron’s spin. When the spins of many unpaired electrons align with each other, their effects add together to create a magnetic area called a magnetic domain. If the alignment is permanent, the material is ferromagnetic.

All magnets have a north pole and a south pole. The magnetic field is directed from the north pole to the south pole of the magnet. Another magnet (or a compass!) that is placed in this field will feel a torque that will push the magnet to align itself with the field’s direction. This results in magnetic attraction!

Magnetic attraction can be used to do some unusual work. Farmers give cows magnets to swallow so that any metal debris in their feed will stick to the magnet and not injure the cow’s stomach lining. This is not recommended for humans!

Things to Try

Watch the video at the following link for idea for some of the patterns you can create:
http://shawnlani.com/WORKS/FFMagnets/FF%20Magnets%20QT/FFMagnets%20Movie.html

Questions to Ask

Can you think of some uses for objects that spin around very quickly? What happens if you spin wet clothes around?

Explore More

Floating in Copper
Explore the slowing effect of eddy currents with your own fingers as you levitate a strong magnet between two pieces of copper.

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