# Racing car example to do with coefficient of friction

1. Jul 12, 2006

### dopey9

A racing track has a corner which is banked at an angle of 30 degrees
cars passing round the corner travel in an acr of a circle of radius 20 metres.
car is travelling at 30 m/s and using g as 10 instead of 9.81

I need to find the smallest value of the coeffiecent of friction needed to prevent the from slipping sideways......but i dont know what forces that i need to use...they havent give the mass the car so im not to sure about the reaction...also air resistance do i include?

Is there any one that can show how to do it the steps and the forces i need to resolve...thankz

2. Jul 12, 2006

### Andrew Mason

When an object moves in a circular path, what force must be acting on it?
AM

3. Jul 12, 2006

### dopey9

Centripetal force is acting on it...is there a formula for this?

4. Jul 12, 2006

### Hootenanny

Staff Emeritus
Try using Newton's second law radially.

5. Jul 12, 2006

### NateTG

"Centripetal force" is IMHO a confusing phrase, generally to be avoided.

It's probably less confusing to say that an object moving in a circular path is has centripetal acceleration. (That is, it must be accelerating towards the center of the curve.)

The usual method for doing this problem is to assume that the car has some unknown mass, say M, and then to draw a FBD of the car on the banked curve, with the understanding that there is some net centripetal acceleration (a function of the car's speed and the radius of curvature).

6. Jul 12, 2006

### nrqed

Hi,

as NateG said, the mass actually drops out at the end of the calculation. So just assume a mass M and work through the problem

It's really hard to explain without a blackboard to draw on. First you really should start with a free body diagram. Let's say one that shows the car heading directly toward you. So that will show the car on an inclined surface. It's heading directly toward you (toward the z axis).
What are the forces? There's the weight, the static friction force and the normal force. That's it! No other forces. Now draw the three forces on the diagram. The static friction force has to be parallel to the surface. But it could go upward or downward, depending on the situation.

I am confused by the question "to prevent from slipping sideways"...Sideway upward or sideway downward?

Patrick