matthen:

You’re on a merry-go-round and you want to pass a ball to someone opposite to you. Looking from above, the ball will travel in a straight line, but to you it will seem to curve in towards them. You ought to throw it towards where they are going to be by the time it gets to them. However if you didn’t realise you were spinning, you might think the ball was experiencing a sideways force, causing it to curve. This effect is called the ‘Coriolis effect’, and it explains why tropical storms always spin clockwise in the Southern hemisphere and counter clockwise in the Northern. [more] [my code]