# Do massive objects in space act as gyroscopes?

1. Jun 15, 2010

### zewpals

I just learned about gyroscopes and their precision this year in Physics. I was just curious since massive objects in space tend to rotate around their own axes and have considerable gravitational forces, do they have a precision movement?

I understand the momentum vector will naturally want to move towards the torque vector But since gravity pulls on every direction of the space-time continuum with equal force, that torque would have a net force of zero, right? Therefore no precision?

And in cases of extremely fast spinning such as neutron stars and black holes...is there an abnormality in precession?

2. Jun 24, 2010

### Archosaur

Angular momentum is conserved in space, just as it is here. For example, neutron stars spin so quickly because their radius has decreased. Also, your reasoning, that a uniform pull of gravity in all directions means no precession, is correct. However, some spinning objects in space do precess, such as the Earth. That's because gravity is not uniform in all directions on the Earth. The Earth's axis shifts about 1 degree every 72 years, just like a giant gyroscope.

3. Jun 25, 2010

### Garth

Hi zewpals!

You may wish to learn about the Gravity Probe B satellite experiment, especially their Spacetime and Spin page.

After that you may be interested in the PF thread Alternative theories being tested by Gravity Probe B.

Garth

4. Jun 25, 2010

### zewpals

Archosaur,
Yes I was familiar with the precession of the Earth but I never really connected it with being a gyroscope haha. Why does the Earth not pull in all directions equally? Is it because other massive bodies further away, such as the sun, pull back?

5. Jun 25, 2010

### Garth

Well, the Earth is an oblate spheroid and not completely spherical, it has an equatorial bulge and even that is deformed into the Geoid. The gravitational tidal forces of the Moon and Sun apply torque as they attempt to pull the equatorial bulge into the plane of the ecliptic. The Moon's gravity acts on the non-spherical moment and causes the earth to precess.

Garth

6. Jun 25, 2010

### Archosaur

What he said.