Can you solve these physics riddles? ft Simone Giertz - Part 1/3

The reason you use a left-handed screw on the left pedal has to do with tangential velocity.  Both pedals are revolving in the same direction; this creates angular momentum.  

Picture a space ship which has a shape similar to a bike tire, only 1000x bigger.  Now imagine we are people walking along the flat inner edge of the tire.  The angular momentum of the space ship is caused by centrifugal force (the space ship is rotating at a constant speed of 8 m/s).  It would push us outward towards the edge of the tire and away from the center of the space ship.  Voila; you have artificial gravity on a ship.

But what does that have to do with the original posited question concerning the left hand screw?  Well, quite a lot actually.  The constant pedaling would apply a force to one direction.  In the case of a screw, you screw it right to get it tight (that's how we learned the proper directions).

So the tangential velocity would gradually, over time, start screwing one screw tighter while unscrewing the other screw.  Thus, the bike makers had to thread a left-handed screw on the left pedal.  Barring a few backwards pedals from time to time (do they even make reverse-brake bikes anymore?  I'm old!), the two screws, left-handed and right-handed, will only tighten with each bike ride.

Hope that helps,

A physics professor.

P.S.  I know someone will comment on how we remembered to tighten and untighten screws.  That's just fine.