Round and round she goes

scott_sieger

Main Question or Discussion Point

[SOLVED] round and round she goes

Hi guys/galls,

A quick question you may be able to help me with.

Has any one got or seen firm theories that explain the earths continuuous rotation as it orbits the sun?

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Janus
Staff Emeritus
Gold Member
Originally posted by scott_sieger
Hi guys/galls,

A quick question you may be able to help me with.

Has any one got or seen firm theories that explain the earths continuuous rotation as it orbits the sun?
conservation of angular momentum.

enigma
Staff Emeritus
Gold Member
F = m a = omega2*r = G*M*m/r^3*r

If you are interrested, I have coded a Matlab script which simulates planetary motion for input-able initial position and velocities (ignoring pertubations).

Last edited:
Phobos
Staff Emeritus
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Welcome to Physics Forums, Scott!

Inertia. (in addition to the above)
The Earth formed in a rotating/revolving state and has continued that way because nothing has stopped it (not much friction in space). As Janus indicated, conservation of angular momentum is the reason the Earth formed in a rotating/revolving state (the original nebula that formed our solar system came together in an asymmetrical fashion which resulted in a net spin & the velocity of the forming planets, with respect to their distance from the sun, determined the characteristics of their orbits).

p.s. Which did you mean...?
rotation = Earth going around its axis
revolution = Earth going around the sun

russ_watters
Mentor
F = m a
In words, that's Newton's 1st: 'An object in motion tends to stay in motion unless acted upon by an outside force.'

scott_sieger
Hi Guys,

I think you are all correct in what you are saying.

It's just that to say the a body retains it's revolving state doesn't explain whay it does retain it's state. Maybe I am looking a little deeper with my questions.

It was stated that the earth formed in a rotational state and has stayed that way since....this is proabably quite correct....but I question why did it form in a revolving state in the first instance.

I'm sorry if I seem pedantic.

What is the energy of inertia?

Phobos
Staff Emeritus
Gold Member
Originally posted by scott_sieger
It's just that to say the a body retains it's revolving state doesn't explain whay it does retain it's state. Maybe I am looking a little deeper with my questions.
The very difference between a scientific law (description) and a theory (explanation)! Good job!

It was stated that the earth formed in a rotational state and has stayed that way since....this is proabably quite correct....but I question why did it form in a revolving state in the first instance.
As I said...the asymmetic collapse of the original nebula resulted in a net spin. Gravity tended to pull the bits and pieces together toward a common center (or many common centers...the sun, planets, etc.). But with tangential velocities going on, particles don't fall straight to a center, they take spiraling paths (orbits). When impacting the center mass, the impactor delivers that energy to the center mass. Never mind dust particles...imagine a collision of a 1-km asteroid into a 5 km asteroid. It would be tough to bring the two together without imparting some kind of off-center movement.

And per the conservation of angular momentum, the more mass you bring toward center, the faster the whole system spins (like an ice skater bringing in his/her arms to spin faster).