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Old September 14 2012, 06:23 PM   #16
JarodRussell
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Re: About planetary gravity

RB_Kandy wrote: View Post
I recently found out that gravity on any given planet is caused by the mass of the planet.

I had always assumed that gravity on a planet was caused by the speed of rotation, orbit, proximity to the sun, and size of the sun.

I began exploring why gravity didn't get stronger during its ellipse when it was closest to the sun, and less when it was far. It was googling that which lead me to realize the size of the planet was the cause of gravity.

But I am wondering, does speed of orbit and rotation play any part of planetary gravity?
Just why did you think that the SUN was causing us getting pulled towards the Earth? Or that the rotation of Earth would pull us towards Earth? Have you ever been on a carousel, and where you pulled inward or outward by the rotation?

Glad you recently found out that gravity is caused by mass.

Now, orbital speed, the planet's rotational speed, the gravity of the sun, the gravity of the Moon, they all affect the gravity of the Earth.

If Earth wouldn't spin, gravitational pull would naturally be a bit stronger. The Moon's gravity pulls on Earth and anything: it causes tides (because the whole body of water is pulled towards the Moon, and the Earth rotates through that water "hill"), earthquakes, and the gravitational friction constantly reduces the Earth's rotation speed. The gravity of the sun affects us more when Earth is closer to the sun, and less when it's farer away from the sun, naturally. But it's a pretty minor difference. And yeah, even the sun causes tides, just like the Moon.
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