From left to right: the thick-walled pipe that came with the magnet; The next three are thin-walled copper; one uncut, one slit along the length and one divided into about 55 rings. The magnet is in front. |
So I went to the hardware store, and bought three 2-foot lengths of copper pipe. These pipes had thinner walls than the one I bought in the toy store. One I left unmolested, one I cut down the length producing a 1.5mm gap, and the last one I cut into 1/2" sections (about 50-60 before I got tired). I slipped the rings onto a thin transparent plastic tube (rolled from a fluorescent-tube cover).
The expectation was that the transit time in the original thick-walled tube would be the longest, and in the thinner-walled tube a bit shorter. The rings would be about the same as the uncut tube, and time through the slit tube would be very short. Here are the results. Since I didn't have a stopwatch, I counted ticks on a metronome. This is very rough:
Tube type | ticks |
---|---|
thick-walled | 15 |
thin-walled | 7 |
slit | 5 |
rings | 3 |
When you look down the tube as the magnet descends, you can see it rotating and tumbling. I decided to restrict the orientation of the magnet, since would also make it easier to think about the problem. I rolled the magnet into a small paper tube that loosely fit inside the tubes, in one of two positions as shown in the figure. Again I timed the transit times with ticks of the metronome:
Tube type | orientation | ||
---|---|---|---|
A | B | tumbling | |
thick-walled | 9 | 14 | 15 |
thin-walled | 4.5 | 6 | 7 |
slit | 3.5 | 5 | 5 |
rings | 3 | 8 | 3 |