# Homework Help: Uniform Circular Motion -Explanatory questions

1. Mar 9, 2007

### Hydroxide

1. The problem statement, all variables and given/known data
A coin is placed on a turntable. When the motor is stated the turntable starts to rotate. Before it reaches full rotational speed the coin flies off. Explain why and in what direction will it go?

And

A pilot of an aeroplane, when pulling out of a steep dive can sometimes black out. This is attributed to the lack of blood to the brain. Explain this in terms of uniform circular motion.

2. Relevant equations

3. The attempt at a solution

Well the coin stays on the turntable because of friction between the two surfaces. It flies off in a path that is tangential to the turntable at the point it leaves. But I'm not sure what is the scientific explanation for why it flies off.

And

I'm stumped by the second question

Thanks, any help is much appreciated

2. Mar 9, 2007

### robb_

First part sounds good. Think about Newton's Laws to finish it up.
Second question is very similar to the first. Why is there a lack of blood in the brain?

3. Mar 10, 2007

### sidrox

as long as $$\frac{mv^2}{r} < Friction$$ or even equal to friction, the coin is going to stay.
Whether or not it is in UCM the velocity is always tangential; so as soon as the centripetal force exceeds friction, the coin will fly off tangentially