Circular Motion Question

1. Mar 4, 2009

chops369

1. The problem statement, all variables and given/known data
This is just a conceptual question:
Give an example of a situation in which an automobile driver can have a centripetal acceleration but no tangential acceleration.

2. Relevant equations
N/A

3. The attempt at a solution
I understand that centripetal acceleration occurs when there's a change in direction, but how can a driver change direction without having a velocity? I think it may have something to do with skidding, but then again, I might be totally off

2. Mar 4, 2009

MrB3nn

Think about the definition of velocity, being a vector. It has a magnitude and direction. Since centripetal and tangential acc'ns are at normals, you can have one without the other. A change in direction with no change in magnitude of velocity (speed) will give you a centripetal acc'n without a tangential one.

3. Mar 4, 2009

chops369

So, would an example be if velocity stayed at a constant 5 m/s and the car turned?

4. Mar 4, 2009

MrB3nn

Yes that would be ok. In the example of a car, there will always be resistive forces i.e. friction/air resistance but if the driver accelerates enough to balance these, his speed will stay constant. If he turns the car there will be a static friction force directed towards the centre of the turning circle, this supplies the centripetal force.