The rules for soap box racing state that the soapboxes must be powered only by the strength of a push and the force of gravity while going downhill. Any form of stored power or external energy sources, including engines, petrol, batteries, electrical cords, catapults, and afterburners, are not allowed. The emphasis is on using the natural forces of gravity and momentum for propulsion. However, this doesn't mean that the soapboxes won't go fast; racers use their design and weight distribution strategies to optimize speed while adhering to these rules.