Eddy current braking effect

A demonstration of the eddy current braking effect using a neo magnet and aluminium.

The aluminium is 10mm x 20mm x 10mm x 1.5mm square U section 95cm length, near vertical (approx 85 degrees)

The magnet is an NdFeB (Neodymium Iron Boron) disc, 10mm dia x 3mm thick.

To give a comparison of the effect, I dropped another magnet alongside on the wood surface. The magent in the aluminium channel takes approx 10 seconds to reach the ground & the magnet on the wood takes a little over 0.5 seconds.

Category:

Howto & Style

Tags:

• eddy
• current
• braking
• neo
• ndfeb
• magnet
• aluminium

[shubus]

Now do it with the opposite pole. You may be surprised.

[stop4stuff]

works the same with either pole

[shubus]

Check to see if it takes the same amount of time to drop when the South is to the metal versus the North is to the metal. You may need a longer run. My 24" aluminum sheet is NOT long enough.

[stop4stuff]

what you're probabloy seeing is th magnet's repulsion & attraction to the earth's magnetic field... place a disc magnet on edge on a smooth surface & the magnet will tumble depending upon its orientation to the earth... the same thing happens with the magnet on the Al.

[stop4stuff]

I marked a magnet with north & south... & tried doing this again at different orientations to the earth's magnetic field... when the magnet is repelling the earth's field, it will tumble at a less steep inclince than when the magnet is attracted to the earth's field.

[99rhetbaboons]

Neat. Still not sure how it works.

[stop4stuff]

Basically, as the magnet falls it creates an electric current within the Al, which in turn creates a magnetic field slowing the magnet.

[shubus]

That's what the rest of us are seeing. No idea why, or what the significance of this is, but is a curious phenomena. Longer length runs are needed. A slightly less vertical angle and the magnet won't tumble but slide dowe.

[th15n4m315t4k3n]

currents'' which flows in a way that opposes the the downward movement of the magnet. Thus a force generates by eddy currents is pushing the magnet up and pulling it up to oppose its changing flux.

[th15n4m315t4k3n]

Lenz's law states ''if a conductor experiences a change in magnetic flux, it will induce a current from the conductors ''freely hanging electrons'' which propagates in such a way that it opposes the change that created it'' therefore in the video we saw a magnet moving down a conductor at a slow rate less than 9.8ms^-1. this is because as the conductor experiences the changing magnetic feild from the magnet it generates ''eddy

[99rhetbaboons]

ah, now see, that's what I'm now finding out. But when this was first demonstrated to me back in 1985 on pbs on a show called "the mechanical universe" (you can still see it on the annenberg website) it was explained to be kinetic energy being used up by the heat energy being created by the current in the copper of the pendulum. Nothing was said about counter magnetism.