Pinewood derby: Difference between revisions

The force propelling a pinewood derby car is [[gravity]] and the only opposing force is [[friction]], therefore car modifications are aimed at minimizing the friction that occurs when the wheel spins on the axle, contacts the axle head or car body, or contacts the track guide rail. Friction due to [[wind resistance]] is a minor, although not insignificant, factor. The wheel [[tread]] can be sanded or lathed and the inner surface of the hub can be coned to minimize the contact area between the hub and body. Polishing the wheel, especially the inner hub, with a plastic polish can also reduce friction. Often one front wheel is raised slightly so that it does not contact the track and add to the [[rolling resistance]]. Axles are filed or lathed to remove the burr and crimp marks and polished smooth. More extensive modifications involve tapering the axle head and cutting a notch to minimize the wheel-to-axle contact area. A proper lubricant, typically [[graphite]] powder, is essential. [[Wheel alignment]] is important both to minimize wheel contact with the axle head and body as well as to limit the contact between the wheels and guide rail as the car travels down the track. The [[center of mass]] of a typical car is low and slightly ahead of the rear axle, which helps the car track straight as well as providing a slight advantage due to the additional gravitational [[potential energy]].