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Name: Mahmoud
Status: student
Age: 20s
Location: N/A
Country: N/A
Date: 1999
Question:
There are two cylindrical slugs of metal were allowed to free-fall down a hollow vertical tube made of copper. One of the slugs, a magnet, took significantly longer to fall through the tube than the other. Why?

Replies:
A changing magnetic field induces an electric field in a conductor. This new changing electric field induces a changing magnetic field, etc. Energy is being transfered from the gravitational field to the kinetic energy of the falling magnet. Some of this kinetic energy is transferred into the generated electric field. Since some of the kinetic energy is transferred, the magnet does not accelerate as it normally would when falling freely in a gravitational field.

There is more information on this subject. Use 'eddy currents' as your keyword.

---Nathan A. Unterman


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