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Message started by thor on 08/21/05 at 21:40:10

Title: circular gravity
Post by thor on 08/21/05 at 21:40:10

If it weren't for gravity, the moon and satellites would fly away from Earth, but this is different than how gravity works on Earth.   I drop something it falls straight to the floor.  At what height does gravity start working circularly rather than straight down?

Title: Re: circular gravity
Post by Valareos on 08/22/05 at 18:35:33

if you threw the ball foward with enough speed to be equal to the foward momentum the moon has, the ball would never touch the ground either!  (well until it hits the mountainside)

That is the main difference between the examples.
Assume the moon has a perfect circular orbit around the earth.

The moon IS falling towards the earth.  But it is moving fast enough foward so that the earth curves away the same amount the moon 'fell'  meaning that it is in a constant state of falling, the ground just keeps curving away.

little bit messier on the fact it isnt a perfect circle, but that is the general idea.

Title: Re: circular gravity
Post by nou on 01/11/06 at 18:59:33

The gravity points tword the center of the earth. The closer, the stronger the gravity. F=1/(r^2). The moon orbits at about 1 km/s , and the orbits close to the ground are a several km/s. Throwing a ball at 3m/s is too slow to notice the deviation from a parabola. If the ball could go through the ground and all the earth's mass was concentrated at the center, the ball would follow a really long thin ellipse.

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