NCU Physics Demonstration Lab 國立中央大學物理演示實驗

Magnet Space Stroll

The magic floating magnet

What?

To demonstrate Faraday’s law and Lens law in an amazing way.

How?

Experiment Setup: An aluminum tube about one meter long, set in vertical position, one magnet, and one Ping-Pong ball.

  1. Let the ping-pong ball free-fall in the tube and observe its motion.

    Experiments demonstration

    ×Experiments demonstration

    post-producing

  2. Let the magnet free-fall in the tube and observe its motion.

    Experiments demonstration

    ×Experiments demonstration

    post-producing

  3. Compare the results of part 1 and part 2.

    Experiments demonstration

    ×Experiments demonstration

    post-producing

Why?

Why the falling speeds are different?

Think...

×Think...


A moving magnet will induce the change of magnetic flux at its surrounding. The induced electromotive force will generate eddy current on the aluminum tube. The eddy current will induce a magnetic field in against with the magnet, so the falling speed is decreased.

Questions

  1. If we use tubes of other materials (ex. plastic, iron, copper,…), what will be the results?
  2. How do the materials influence the falling speeds?
  3. If a weight is attached on the magnet, will this change the falling speed?

About the Experiment

You may compare this experiment with the experiment E05 Pendulum Stop, and experiment E06 Flying Aluminum Foil in this website.

Reference

  1. H. Benson, University Physics, Rev. ed., John Wiley & Sons, 1995, USA., Ch31.

Producer

v.1 Mr. Zeng (曾前助理)

Advisor

Ching-Chi Chu (朱慶琪)

Written by

Shi-Lin Huang (黃時霖), Ching-Chi Chu (朱慶琪)