1. May 15, 2004

### Jonh Doe

I need some information about the coefficient of circular or rolling friction for rubber on tarmac (or asphalt). It is to do a measurement of the force required to move an object of certain weight at regular speed on wheels.

I know that rolling friction is about 1/100 of the kinetic friction coefficient, and that this coefficient for rubber on tarmac is around 1.08, but I need a more precise measurement, and dont have access to such information.

If you could tell me this coefficient, or where I could find a way to calculate it or a chart that has it, it would help me. By the way, I cannot do the measurement directly, since the weight to move is around 1000 kg, and I dont have the required instruments.

Also, I would need help in how to measure the drag of air on an boject, if you know how.

2. May 18, 2004

### MathematicalPhysicist

im familiar to static and kinetic friction, what is rolling friction?

3. May 18, 2004

### turin

Just as a suggestion, you might have a relatively easy way to make this measurement. You could construct a simple contraption using one of those suspension springs and a simple frame (of wood or whatever). Then you could pull the car (at some constant speed, say 2 mph) and mark the stretched length of the spring on the frame. This together with the spring constant should give you 2 sig figs worth of determination. This may not work very well if the spring constant is too low or too high. The force you measure will be the rolling friction and the axle friction (not to be confused with each other). To get just the rolling friction of the tires, you could have them roll down a slight incline and record the time, but the deformation of the tires under the weight of the car would be absent, so I'm not sure this would be very accurate.

4. May 19, 2004

### TALewis

In college, I think we called it the coefficient of rolling resistance, Cr, the fraction of the car's weight needed to maintain a constant velocity:

$$C_r=\frac{F}{W}$$

To get a rough estimate, we used a bathroom scale that we pushed on to measure the force needed to keep the car rolling.

5. May 19, 2004

### turin

Ah, that is much simpler and more available than my idea!

I don't know why I always try to make things so complicated.