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Spinning coins



Ever been really bored and done something really random? Ever been really really bored and pondered the physics of said random act? I know I have. Just the other day while sitting at a table, I got bored and had a penny in my pocket, so I decided to spin it on the table in an attempt to satisfy my boredom. After about five minutes I made some interesting observations. One thing I noticed is that every time it spun, it would slide across the table. At first I thought this was because the table was at a slight angle, and gravity was causing it to slide down, but after some closer observations I learned that this was not the case, as the table was level. After some more thought I figured it out. Every time I would spin it, the reason it would move was because its axis of rotation was not 100% perpendicular to the table. Because of this, the edge of the coin that was touching the table had a frictional force acting opposite of the direction of the edge's tangential velocity, causing it to accelerate and move along the table

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Very interesting! I'd never considered the rotational axis of a spinning coin before. I had to try it out as soon as I read your post, neat! :money:

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