12+
Gallery 2

Floating in Copper

Use your fingers (and an electrical field) to keep a magnet suspended in mid-air between two long conductors.

How it works

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

Things to try or ask around the exhibit

  • Try floating the magnet from one end of the copper to the other.
  • How quickly can you make the lower magnet move by dragging the upper magnet along the copper?
  • This exhibit contains a strong magnet! Please keep credit cards or any devices that might be affected by magnets, away from this exhibit.
  • Make sure the lower magnet is sitting horizontally between the copper slabs before you try floating it.

Background

When a magnet is moved near a conductor such as the copper slabs, 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 magnet to slow down as it moves toward the upper magnet, creating the ‘floating’ appearance.

This slowing effect is used in eddy current braking systems. These systems have the advantage that they don’t wear out as do friction brakes. The braking effect is proportional to the speed of the conductor’s movement relative to the magnet. A fast spinning wheel experiences a stronger braking effect compared to a more slowly spinning wheel. This means that a vehicle’s braking speed is smoothed as it slows down to a stop. Eddy current braking is quite an inefficient process, as it converts kinetic energy to heat energy.

Finding the science in your world

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.