Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Magnetic Free Fall
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:
The moving magnetic field induces an electric current in the surrounding conductor, and the magnetic field resulting from this "eddy current" opposes the field of the falling magnet. If the conductor were a superconductor, that is, if no energy were lost by the induced current, the induced magnetic field would be able to completely prevent the permanent magnet from moving. This is the principle behind magnetic levitation. You question sounds like a homework question; for the actual equations governing this behavior, look in your physics book under "eddy currents" or "Lenz's Law."

Richard Barrans Jr., Ph.D.


The changing magnetic flux sets up eddy currents in the copper which produce their own magnetic field opposing the change in magnetic flux. This produces a force on the magnetic slug.

Tim Mooney



Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory