Lenz's Law Demo
If you drop the little metal slug down the copper tube, it falls under the pull of gravity, and drops out at the bottom, just as you would expect.
But take the second, apparently identical, slug; drop it down the tube, and hey presto! the slug travels down the tube extremely slowly. You can even see it's slow passage via the window in the side of the tube.
It is a great magic trick, but the truth is just as amazing. The second slug is highly magnetic. Now Michael Faraday, the British physicist, discovered as long ago as 1831 that when you pushed a bar magnet into the opening within a copper coil, an electric current was produced within the coil. This is known as electromagnetic induction.
The Russian physicist Heinrich Lenz observed that the direction of the induced current in a conductor is always such as to oppose the motion which produced it.
So as the magnetic slug moves down the copper tube, a series of transient "eddy currents" are induced in the copper tube, and these currents will create a magnetic field that opposes the downward motion of the slug.
CONTAINS MAGNETS. SUITABLE FOR CHILDREN 14 YEARS AND OVER