### Earth Orbit

Follow in the steps of Newton and find the path that the earth follows around the sun.

### Gravity Paths

Where will the spaceman go when he falls through these strange planetary systems?

### Motorbike Momentum

A think about the physics of a motorbike riding upside down

# Whirlyball

##### Age 16 to 18Challenge Level

See video [mediaplayer avi - 3.4MB] [quicktime - 0.5MB] [ipod - 1.3MB]

A ball of mass $m$ is attached to a light inextensible string of length $l$. The ball is whirled around so that it moves in a horizontal circle with constant angular speed $\omega$.

Find the angle $\theta$ between the string and the vertical. Show that the angle $\theta$ is given by $\cos^{-1}{g\over l\omega^2}$.

Now increase the angular velocity. What happens to the ball?

What is the smallest angular velocity with which the ball can whirl in a circle on the end of the string in this way?