Why doesn't the Earth fall apart?

Originally posted by Cyberbian
The answer is not so difficult as all that.

You have factored the properties in the wrong order, You underestimate the power of earth's gravity.

Stop the Earth's rotation and you will feel the full force of gravity. you are currently in a state of balance between gravity, which is slightly stronger than the centrifugal force which would throw you into the air. Were that force to weaken and you would be cast into the air along with all loose bits of the earth. loose your momentum and be pulled back to earth by gravity in a greate grinding machine of a planet!

The fact that we have not found such planets, suggests that the grinder would consume some of the rotational energy and slow the rotation to a more stable speed. Hence balance where stability wins out.

Cyberbians law of planetary physics, rotational energy always falls to a level where gravitational force wins over centrifugal force.



[edit on 1-6-2009 by Cyberbian]

This post is a little misleading. Unintentionally I'm sure. If the Earth were to stop spinning, you would not feel an increase of weight due to the loss of centrifugal force. Indeed, your weight would increase, but not by enough to feel, or probably even measure. People who make it to the South or North Pole do not feel themselves get heavier.
I just wanted to clarify incase there was anybody who imagined feeling crushing gravitational forces if they were at one of the poles.

[edit on 1/6/2009 by Recouper]

Originally posted by Cyberbian
[

Gravity does not originate at the center of the Earth.

Every bit of earth has it's own gravity, were you in the center of a hollow and evenly distributed planet, you would be weightless due to the evenly distributed gravity. Therefore as you go deeper toward the center of the Earth, you become lighter and lighter.
[edit on 1-6-2009 by Cyberbian]

true but the core being a large solid mass would have a great gravitational pull.

whats heavier, the outer mantle or the inner core.

Gravity is what holds it all together and gravity is a property of mass, demonstrated by denser objects having greater gravity per unit volume. When centrifugal and centripetal force are in equilibrium we can achieve orbit and the centifugal force is described as V^2/R which must, for orbit, be equal to to the gravitational acceleration of approx 9.m/sec^2 for near earth orbits at least.

The required V for a low orbit of, say, 100km altitude is close to 7 miles/second which is far faster than the earth's speed of rotation at the equator therefore gravitational centripetal force wins by a huge margin, more than an order of magnitude - sufficient to hold the oceans and everything else firmly on the surface.

Added some numbers which might explain it better:
Earth's radius at the equator 6.378 x 10^6 metres
Circumference (equator) 40.1 x 10^6 matres
at 1 revolution/day speed at equator = 40.1 x 10^6/86400
= 463.8 metres/sec

centrifugal acceleration = V^2/R
= 463.8^2/6.378 x 10^6 = 0.0337 m/sec^2
or 0.0337/9.8 = 0.0034 -ve g's

Therefore you'd weigh 0.3% more if at the north or south pole which is really insignificant

To achieve orbit or weightlessness you'd need to move fast enough to produce 9.8m/sec^2 -ve g's which amounts to:
sqrt(9.8 x 6.378 x 10^6) = 7906 metres/sec or 28642 km/hr (17688mph)

For the earth to fly apart it would need to rotate at that speed or faster which would make 1 day last about 1.4 hours or less.


[edit on 1/6/2009 by Pilgrum]

[edit on 2/6/2009 by Pilgrum]

reply to post by Mozzy


You replied right under my post which explained everything...