gravitational pull in our solar system

[Perpetual Motion]

If the world has enough gravitational pull to keep the moon in orbit then how can we send satellites into space?

And if the sun has enough gravitational pull to keep planets much further away from the earth in orbit then why does the moon not just orbit the sun?

I'm really confused

[DrRocket]

If the world has enough gravitational pull to keep the moon in orbit then how can we send satellites into space?

And if the sun has enough gravitational pull to keep planets much further away from the earth in orbit then why does the moon not just orbit the sun?

I'm really confused

 

You need to read a book on orbital mechanics.

 

Orbital Mechanics by Prussing, Conway and Prussing is a good one.

[md65536]

If the world has enough gravitational pull to keep the moon in orbit then how can we send satellites into space?

To get to space: Rockets typically have an acceleration away from Earth that's much higher than gravity's is toward the Earth.

To stay in space: The satellites are accelerated to a speed that's faster than the moon's speed relative to the Earth.

It takes a lot of energy to get to orbit, and none to stay there.

 

And if the sun has enough gravitational pull to keep planets much further away from the earth in orbit then why does the moon not just orbit the sun?

The Earth and moon each orbit around their barycenter, which I guess orbits the barycenter of the Earth/moon system + the sun.

 

Orbiting is like being in freefall; there's little gravitational proper acceleration (it is "microgravity").

So, while you have a system like the Earth/moon orbiting something like the sun, part of the system (eg. the moon) isn't going to be pulled away to the sun, because the gravitational pull of the sun affects the Earth and the moon equally. Note: Not exactly equally... you do have gravitational gradients, which causes tides, which is an effect of gravitational masses pulling non-uniformly on a system.

 

The above should be true for any moon around a planet. In the case of Earth's moon, the moon orbits Earth slow enough relative to the Earth/moon's orbit around the sun, that the moon effectively does orbit the sun. If you look at the path of the moon around the sun, as shown here: http://en.wikipedia....Moon_around_Sun, you'll see that it looks very circular, such that its orbit around the Earth is only a relatively slight deviation from an orbit around the sun.

Edited December 31, 2011 by md65536