AspenPhysics and the Tour

Dear Editor:

Like everyone else I have been watching the Tour de France. This morning there was an interesting mistake in physics, which seems to be widespread. Thor Hushovd was chasing Jeremy Roy (odd first name, that) and the commentator said that Hushovd now had a chance of catching up because he was heavier and they were going downhill. Heavier has nothing to do with it.

Think of the high school physics experiment where a penny and a feather are dropped in an evacuated vessel. They fall under gravity with the same acceleration. Two bike riders in a vacuum under the influence of gravity alone also come down a hill with the same acceleration. There is rolling friction from the tires but that too does not change this. The only thing that does is air resistance. Insofar as Hushovd came down faster, it was because he had a better aerodynamic position and took a more daring line.

Jeremy Bernstein