The Weight-

Powered

Vehicle (WPV)

HOW FAR CAN A CAR GO
ON ONE FOOT-POUND
OF ENERGY?
BY RICHARD B. GRAEBER

After my son won his high school science class mousetrap-powered vehicle (MPV) competition, I asked him if he knew what a foot-pound of energy was. He gave a vague answer that didn’t really nail it. Admittedly, a foot-pound (ft-lb) is an abstract concept — where do you get a pound of feet from anyway?

Construction

My son and I built the car from pinewood we picked up at the hardware store. We also bought a wooden yardstick, and we found lead sinkers and monofilament fishing line at a sporting goods store. The local hobby shop supplied us with wheels, a small pulley, aluminum tubing for axles, and polypropylene tubing lubricated with teflon powder for bearings. We used these parts, along with a few other odds and ends, to cobble together our experimental vehicle.

Photograph by Ed Troxell

To illustrate what a foot-pound of energy is and what it can do, I designed a vehicle that derives its propulsion from a falling weight (rather than an unwinding spring as used in an MPV).

This small car, which I call a weight-powered vehicle (WPV), demonstrates the conversion of potential energy into kinetic energy in one of its most rudimentary forms, leading to a better understanding of energy conversion and loss.

74 Make: Volume 20