I encourage my students to be observant and bring interesting problems to
class. This afternoon one of them brought the following:
In the lab are some wheel and axles from old Hall's carts, two 2-cm steel
disk wheels attached to a 5-cm steel axle. He put one of them on an inclined
board, about 15 degrees incline, and it rolled down the board. Next he
turned the wheels about 20 degrees to the slope, and it rolled down 20
degrees to the slope. His question, and mine to anyone who wants to play
with it, is why does the thing roll sideways? We solved it to his
satisfaction, but not really to mine.
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