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Physics
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Neat-o, mosquito!Registered User regular
Neat-o, mosquito!Registered User regular
OK a few questions here for people that know a bit more about physics than I do....
How is the gravity of a planet related to how fast it rotates on its axis and how quickly it moves in its orbit?
Gravity would increase if the mass increases right? Would it also increase if a planet spun faster? Like....if we could increase the rotation of earth around it's axis, would the gravity on earth increase? If we slowed it down would gravity lessen?
Or do we not know enough to make this statement?
Equations please!
How is the gravity of a planet related to how fast it rotates on its axis and how quickly it moves in its orbit?
Gravity would increase if the mass increases right? Would it also increase if a planet spun faster? Like....if we could increase the rotation of earth around it's axis, would the gravity on earth increase? If we slowed it down would gravity lessen?
Or do we not know enough to make this statement?
Equations please!
| Zinnar on most things | Avatar by Blameless ClericPsycho Internet Hawk wrote: »
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http://www.newton.dep.anl.gov/askasci/phy99/phy99x82.htm
Gravitational force between two objects is a function of the mass of the objects and the distance between their centers.
I guess at relativistic speeds, velocity would affect mass and therefore affect gravity, but a planet isn't going to be travelling that fast. I suppose that if you were on a spaceship and flew by a planet, you would experience a greater gravitational pull the closer to light speed you travelled.
Rotation can cause magnetic effects but that's separate from gravity.
There's lots of good stuff on orbits
http://en.wikipedia.org/wiki/Kepler%27s_laws_of_planetary_motion
Sweet, I got it backward....faster spin means "less gravity" in that the earth would be exerting enough force on us to counter its own gravitational pull and if it slowed down gravity would "pull more" meaning that we would weigh a bit more.
Awesome.
I can't seem to choose the right equation- which formula describes the phenomenon wherein you spin a ball on a string and it has more force acting on the end of the string?
Is that uniform circular motion?
Force between two bodies due to gravity:
F= Gm1m2 / r^2
So it depends on a constant, the masses of the objects and the distance between them.
Does rotation effect (affect? I always get those mixed up) any of these?
I've studied any relativity since I was an undergraduate but as you approach the speed of light your mass increases (so you need to put in infinite energy to get something with a finite non-zero mass to get something up to light speed). Given that your frame of reference is essential in such considerations, I'm reasonably confident in saying that if you spun up a planet to something approaching c it'd do bugger all to its interactions to other bodies in the rest frame.
This is centripetal force, which might be what you want.
I don't think a ball rotating on the horizontal plane would exert any additional vertical force on the end of a string it's hanging from. We need diagrams
Wow. Magic
What? I may have described it incorrectly- but what Runn1ngman posted was what I wanted.
Ok, then...if a ball is hanging freely on a string, the vertical force won't be affected by any spinning. The string is exerting a force equal and opposite to the force of gravity on the ball. Now, something had to start that ball spinning in the horizontal plane, so there is a force involved there, but it's independent from what's happening with the string.
(this all asumes a perfect frictionless environment, and also of course assumes that the string is attached to a frictionless swivel that allows it to rotate. Otherwise the string is winding and unwinding an you'll have a sort of pendulum effect)
So, it wouldn't work at the in-laws' house over Christmas?
Hi-yooo!
The slight difference (20km or so) in the distance between the center of the earth and sea level at the poles and at the equator means that you actually weight about a pound more at the north pole than you would at the equator.
To answer your question, gravity itself wouldn't change with a change in rotational velocity of the Earth, but the sum of the forces acting on your body would change because the centripetal force would be different.
Keplers Third Law states that the square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit (all planets move in ellipses(Keplers first law)).
I can write down all the equations and shit if you like but the end result (according to my notes) comes down to:
T^2 = (4pi^2a^3)/GM
Where T is the orbital period, a is the semi-major axis distance, G is the gravitational constant and M is the mass of the orbiting planet.
SO the time is takes for a planet to orbit once is proportional to the square root of the mass of the planet.
I hope thats right and it almost definitely didn't help but seeing a thread about something related to what i've been doing today made me wana post this :P
In approximation, all objects in the same stable orbit of a much heavier object will have the same speed. This means for instance that there's only 1 height around the earth that's geo-synchrous (The rotation speed of the earth is equal to the stable speed of the orbit).
Sorry to prolong this thread hijack!
Careful with that one. "Theory" just means it's a *generally accepted* explanation for a natural phenomenom. However, that doesn't mean that the current description of gravity is completely correct. For example, they are still trying to understand the mechanism that gravity actually works by (space time curvature? gravitons? both explain results!) In addition, all this stuff about "dark matter" can be cleared up (one of many ways) with a simple correction to Newton's laws on extremely huge distance scales, like, galaxy sized. In fewer words, a different theory.
Sorry if this is long, but this kind of question should either be in A) D&D or
Yeah you're right, my bad, on looking at my notes it is the mass of the star it's orbiting.. damn!