# Understanding of rotational motion

1. Dec 2, 2003

### acoult

Hello anyone that can help. I am trying to gain an understanding of rotational motion, including (tangential speed, angular momentum, centripetal force and so on). The first question I was hoping that someone could help me is:

An automobile speedometer is configured yo read speed proportional to the rotational speed of its wheels. If larger wheels are used, will the speedometer reading be higher, lower or the same.

I understand the question but I was hoping someone could help explain this to me in a mathamatical equation.

Thank you for your help. I promise not to bug you guys to much!

2. Dec 2, 2003

### Ambitwistor

The question is slightly ill-posed, since it didn't specify what is kept the same when the wheels are changed. But I assume they mean that the ground speed of the automobile is kept the same. The ground speed is the same as the tangential speed v of a point on the wheel. By $v = R\omega$, the rotational speed &omega; must decrease if R increases, if we hold v constant.