Gravi Car

A falling weight propels a car forward.

What it shows:

Gravitational potential energy can be converted into mechanical kinetic energy.

gravi car

How it works:

A Gravicar is a vehicle powered by gravitational potential energy that it stores in a 2.5kg mass on a thread which is coupled to the car's rear axle via a pulley atop a high platform (see figures 1 and 2).As the mass falls the thread, which is wrapped around the axle, turns the wheel and accelerates the car. When the mass hits the floor, it is released and the Gravicar moves on with constant velocity.

figure 1: the Gravicar

gravi car

Setting it up:

The mass is lifted by wrapping the thread around the rear axle, securing the end using the catch illustrated in figure 2. The rear wheel will need to be chocked.

figure 2: release catch

gravi car


Everyone should build their own Gravicar to their own specifications out of any old scrap; our rear axle is an old cable reel. The mass needs a padded base because it can land with a thud. The release mechanism, designed to let the mass and thread go free when they hit the ground, leaves a lot to be desired; too loose and the mass drops early, too tight and it gets dragged along the ground acting as a very efficient break. Just right, and it glides like a well tuned Ferrari.