Traffic

Imagine being on the center-strip of a divided highway. Traffic goes by on both sides in a counter-clockwise sense: facing either side, it travels toward your left. The angular momentum of a moving particle is r x (mv) where r is the position vector of the particle from a reference point. In the traffic example, a point between roadways gives you an easy way to see the counterclockwise rotation, but any reference point would work. Consider two cars, same m and same v but going in opposite directions along straight lines distance d apart. You should be able to show that magnitude of the total angular momentum vector is dmv with respect to any point. And if you think about the directions, you will find that US traffic has angular momentum up. In Great Britain, Japan and Australia, traffic goes the other way and the angular momentum is down.

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My other main pages:

fluids, heat, electricity and magnetism
vibrations and waves
quantum

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