06 April 2008

The Physics of Pinewood Derby Cars

As a Cub Scout I made Pinewood Derby cars, but unlike Clifford Lazar I didn't approach the Pinewood Derby from an engineer's perspective.

Hypothesis: for Pinewood Derby cars, air drag is irrelevant; most slowdown is due to rolling resistance and the wheels bumping up against the track as the car wobbles.

Strategy: cut grooves into the axles to reduce the axle-wheel contact area, and grease the axles up well. To reduce wobbling, increase the angular momentum (around a vertical axis) by placing weights at the very front and very back of the car.

Validation: Cliff's car placed second one year and an improved design placed first, showing up a bunch of cars that looked like drag racers and that had been tested in wind tunnels.

Moral: engineers are great.

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