# Homework Help: Gravity probe b gyroscope

1. Mar 15, 2004

### powerball

In GPB's experimental conditions, a negligible amount of precession takes place.

So in terms of rotational inertia, why does the spin axis of a gyroscopes remain pointing in the same direction?

Also, why would changes in space-time cause the axis to change?

Thanks

2. Mar 16, 2004

### powerball

Actually i understand the second part, just not the rotational inertia bit

3. Mar 16, 2004

### da_willem

Because of the conservation of angular momentum. In absence of a torque the angular momentum of the gyroscope is conserved. This is basically the rotational analog of Newtons second law for conservation of 'normal momentum' in absence of a force.

The angular momentum, which is a vector, points in the direction of the spin axis, because it is the crossproduct of the radius and momentum of the gyroscope. In absence of a torque the gyroscope will spin with a constant speed AND direction. So the spin axis of the gyroscope will remain pointing in the same direction.

Last edited: Mar 16, 2004