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Falling magnet demo

Hi Phys-lers:

Others have posted:


I tried a classic demonstration of dropping a magnet through a copper
tube at the same time as dropping an unmagnetized bar. They both
landed at the same time.

I think this demo is normally done with neodymium supermagnets. The
magnet should be a stubby rod in shape, with only a small clearance around
the tube, a "slip-fit" in other words.


We use 1.27 cm diameter neodymium supermagnets in regular 5/8" O.D. copper
conduit and it works great. A second copper conduit has 5 mm hole drilled
every 5 cm for the first 0.75 of the length and then every 1.0 cm for the
rest the the way. There is a noticeable increase in speed the last 0.25 of
the length.

In Honors physics, this demo follows the test over electromagnetism because
one of the questions asks them to predict what will happen compared to a
steel marble falling through the tube and explain why (Calculator not
needed here). Having to think about it in a testing situation helps them
enjoy the demo even more than normal (even if they got the question wrong).
Their comments always of the order of "Neat !" "Cool !"

I think Pasco has a grooved Al track down which you can roll a neodymium
magnet which the students can see.

Lowell Herr wrote:


I must tell a story on myself about the "Falling Magnet Demo." When I
first did this experiment (fortunately without students present) I use a
metal clamp to hold the rod. When I dropped the "cow magnet" through the
tube, it never did come out the bottom. I got a good laugh in private.

This actually happened in class to a good friend of mine and I'm sure Bruce
I will not mind my mentioning it since he told us about it at a Physics NW
meeting.

Bye, DiRT

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David R. Thiessen FUN + PHYSICS = PHUN
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