Levitating Magnets:

Eddy Currents

 

Eddy currents defy gravity and let you float a magnet in midair. Think of eddy currents as brakes for magnets. Roller coasters use eddy currents to slow down fast-moving cars on tracks and in free-fall elevator-type rides.

Materials

  • Neodymium magnets
  • Copper pipe
  • Plastic, wood, and aluminum metal sheets
  • Stopwatch or timer

Experiment

  1. Make a ramp from a plastic sheet (like a cutting board, or whatever you have around) by propping up one end.
  2. Place the magnets at the top. How long do you think it will take for the magnets to reach the bottom?
  3. Write your guess here:_____________
  4. Now release the magnets, timing how long it takes to reach the bottom. Write your answer here:______________
  5. Make a wood ramp, like a wood cutting board or even a coffee table that you can raise one end so it’s higher than the other. How long do you think it will take your magnets to reach the bottom? Write your guess here:____________
  6. Release the magnets again and write your answer here from your stopwatch timer:____________
  7. If you have a cookie sheet, it’s probably steel, so prop one end up to form a ramp and place the magnets at the top. What happened? __________________
  8. Take your aluminum sheet and lift up one end. Place your magnets at the top of the ramp and let go. What happened? Repeat this experiment and this time, use your stopwatch to time how long it takes for the magnets to reach the bottom: ___________________
  9. Now try something else: take a non-magnetized object, like a nail or pencil and slide it down the metal ramp. Did they slide down faster or slower than the magnets?_________________
  10. Grab your copper pipe and stand it on end. Place your magnets at the top and get your stopwatch ready.
  11. Release the magnets inside the pipe and release them, timing how long it takes for them to reach the bottom. Was it faster or slower than the aluminum metal plate? Write the time you measured here:______________

 

What’s Going On?

If this experiment has you scratching your head in confusion, here’s the basic idea about the science behind this effect (which is actually quite complicated!)

When a magnet moves near an object that conducts electricity (usually metal), it creates electric currents called eddy currents which start to flow in the conductor.

These eddy currents create magnetic fields in the opposite direction of the moving magnet, slowing an object down so it appears to float down the ramp slowly.

Eddy currents are brakes for moving magnets!

 

 

Questions to Ask:

  1. What is the average speed of your fastest magnet?
  2. What makes the magnet slow down the most? Is it the size of the magnet, the strength of the magnet, number of magnets, or something else?
  3. What if you stack two aluminum plates on top of each other and use this for a ramp? How would this affect your data?
  4. Does the angle of the ramp matter?