# Homework Help: Car physics

1. Dec 31, 2003

### carcar2

I am doing a science experiment dealing with car physics.

The experiment I am doing involves battery-powered toy cars approximately the size of a hand (four-wheel drive). I am not sure
what effect the weight distribution has on the acceleration of the car. To be more specific, I am looking for the effect of weight/downforce applied to either the front or the back on weight
transfer/traction.

I am attaching weight to the front for one kind of a car(Car F) and the back for another(Car B) and testing the time of the two in a straight-line race. According to my data, the car with the weight attached to the back(Car B) is faster. The only explanation I can come up is that the time which it takes for the weight transfer to take place for the car with weight attached to the back(Car B) is less than the other car(Car F), which makes Car B to accelerate faster. Would you explain why the difference took place?

Also, I am not sure if the traction caused by downforce in the front or the back has any different effect on the speed.

2. Dec 31, 2003

### enigma

Staff Emeritus
Hi carcar, welcome to the forums.

Is it possible that the cars aren't perfect four wheel drive? Maybe more torque is going to the rear wheels. That would explain the difference.

3. Jan 1, 2004

### phatmonky

As a car nut (a real one, not toys :p), I could have told you, that all things being equal, the car with the weight on the back will accelerate faster.

Rear engined dragsters are the top runners for a reason :)

Weight transfer, as well as traction come in to play. Assuming you are getting consistant answers, I would say that your experiment went as planned.
Traction doesn't come into play as "downforce" because frankly these cars aren't moving fast enough. This does matter in the 'launch' (the initial take off), as the weight on the rear will be greater due to transfer, and thus the more weight on the rear means more traction on the tires that will be contacting the most. This is how it works in the real world, but I do believe that wheel spin on your toy car, even if it weren't 4x4, would be negligible, but who knows :p

Swap weights on the cars, and see if you get the same results.