How does gravitational anomalies affect a planet's rotation?

[Bjarne]

How is the kinetic energy of a rotation planet (e.g; the earth) calculated?

 

[tiny-tim]

Hi Bjarne!

How is the kinetic energy of a rotation planet (e.g; the earth) calculated?

But why would anyone want to calculate it?

It's not as if anyone would consider trying to change its orbit, is it? ​

KE of a rotating body = 1/2 mv² + 1/2 Iω²

where I is the moment of inertia of the planet about its polar axis, and ω is the angular velocity

(don't forget to include both the spin and orbital angular velocity, eg the Earth's is 2π x 366.25 radians per year, not 2π x 365.25)

 

[Bjarne]

Thank's tiny-tim
Is it possible that angular momentum affect the rotation of planets?
Does it exist rotating Moons?

 

[tiny-tim]

the angular momentum of a planet about its star (or a moon about its planet) is constant …

this is because the rotational version of Newton's second law says …

torque = rate of change of angular momentum​

and since the torque (moment) of the gravitational force is obviously zero (about the star), the angular momentum cannot change

 

[Bjarne]

the angular momentum of a planet about its star (or a moon about its planet) is constant …

this is because the rotational version of Newton's second law says …

torque = rate of change of angular momentum​

and since the torque (moment) of the gravitational force is obviously zero (about the star), the angular momentum cannot change

What I had in mind, what about if a planet or a star had a heavy gravitational anomaly at the surface, a tidal wave, a mountain a crust density anomaly etc.. This would make the planet heavier in the one "end" as in the other "end" .

Would that not cause larger angular momentum in the "heavy end" of the planet, and cause a planet to rotate.

For example the Moon, the more massive side of the Moon point in the direction of the Earth.

Imaging the massive part was pointing opposite and the orbit speed of the Moon would be 30 times faster, - would that not cause the Moon to begin to rotate ?

 

[tiny-tim]

What I had in mind, what about if a planet or a star had a heavy gravitational anomaly at the surface, a tidal wave, a mountain a crust density anomaly etc.. This would make the planet heavier in the one "end" as in the other "end" .

Would that not cause larger angular momentum in the "heavy end" of the planet, and cause a planet to rotate.

a tectonic plate movement (an earthquake) would alter the moment of inertia (the distribution of mass) …

since the angular momentum must remain constant, that would alter the period of rotation (the length of the day)

(of course, this has nothing to do with energy)