rubber band/mousetrap car wheels?

Question

i have to build a rubber band car for distance.
is it better to have 3 or 4 wheels?
what is the reason for this, or does it matter?

Answer 1

When I was in EE school the best one of these cars I ever saw was built using three 33 1/3 rpm vinyl records as wheels. The car covered the entire track and bumped into the wall beyond the end. No other car came close.

The axles had Teflon bearings. The moment of inertia of the records was high, so it barely started out. Once rolling though, it seemed to have te best conversion of energy from the mouse trap to kinetic energy. Also, since the records created wheels that were large in diameter, the number of revolutions was less, so there was less loss due to friction. Since the speed was lower, there was less loss due to air resistance, too.

Good luck

j

Answer 2

Yes. Cars can be struck by lightning. No. The tires do not protect them. Think about this for a moment, a giant electric spark just jumped through a VERY LARGE distant. What is going to keep it from also jumping the twelve inches or so of air gap from the car to the ground? Besides which the carbon black used in the tires to make them black (you did know that both natural and synthetic rubber are black because of the additives, right?) is very conductive at the voltages involved so they don't do that good a job of insulating the car in the first place. That said the metal of the car might protect you from the lightning by shunting the electricity around you. I say might because the metal is discontinuous and is not a perfect Faraday cage.