## Gravity. Ouch.

Topics that don't fit anywhere else.
Gathon.zypher
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### Gravity. Ouch.

Alright...

Now if I have two masses in space, and I know the radius between them, I can use the equation:
F = GMm/R²

It's Newton's Theory of Universal Gravitation, and it's used to calculate force.

If one body is traveling too fast around it's central hub, it will speed off. Yet if it's too slow, it will simply crash into the object it's orbiting around. Not a complex idea by any means.

Now my question is pretty simple - Starting with the force between my planet and its star, how do I figure out a good speed so that my planet will have a perfect orbit around it's star?

Thank you so much!
Brent

stapel_eliz
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What formulas and constants have they given you for this exercise?

Thank you!

Gathon.zypher
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### Re: Gravity. Ouch.

I'll use the Earth and Sun as an example.

Sun (M) 1.9891×10^30 KG, or 1,989,100,000,000,000,000,000,000,000,000 in non-scientific notation.
Earth (m) 5.9736×10^24 KG, or 5,973,600,000,000,000,000,000,000 in non-scientific notation.
G = 6.67*10^-11, or 0.0000000000667 in non-scientific notation.
r = 149,597,892 kilometers

Force between Sun and Earth
35,413,401,385,356,974,509,164,227,084.496

Circumference of orbit is 939,951,276.999 in kilometers.
Travel time is 365.26 days for a full orbit.
2,573,375.888 Kilometers per day.

Now...

There is a relationship between the speed and the force. The further away from the sun a planet is, the lesser the force between them. The lesser the force, the lesser the speed of the orbiting planet.

Does anyone have an equation where I can punch in the force and get a travel speed?

Thanks!
Last edited by Gathon.zypher on Mon Jun 29, 2009 8:53 pm, edited 1 time in total.

Gathon.zypher
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### Re: Gravity. Ouch.

Alright. Here's another one:
Earth (M) 1.9891×10^30 KG, or 1,989,100,000,000,000,000,000,000,000,000 in non-scientific notation.
Moon (m) 7.347 7×10^22 KG, or 73,470,000,000,000,000,000,000 in non-scientific notation.
G = 6.67*10^-11, or 0.0000000000667 in non-scientific notation.
r = 384,400 kilometers

Force between Earth and Moon
65,966,847,978,416,300,224,900,137,625,457

Circumference of orbit is 2,415,256.432 in kilometers.
Travel time is 27.322 days for a full orbit.
88,399.694 Kilometers per day.

stapel_eliz
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Are you trying to do an exercise using or requiring the formula for orbital velocity...?

Gathon.zypher
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### Re: Gravity. Ouch.

YES!!!! That's it! THANK YOU SO SO MUCH!!!

Gathon.zypher
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### Re: Gravity. Ouch.

Alright... One more question.

Does anyone know how to calculate a planet's surface heat according to heat of its sun, distance from that sun, and atmosphere of that planet?

Martingale
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### Re: Gravity. Ouch.

Alright... One more question.

Does anyone know how to calculate a planet's surface heat according to heat of its sun, distance from that sun, and atmosphere of that planet?

Hows this

Gathon.zypher
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### Re: Gravity. Ouch.

Four words:
I love you all.

THANK YOU SO MUCH!!!!

I am now well on my way to making my own theoretical solar system!