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Gravity Question... kind of 
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#1
Mar1107, 12:41 AM

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Every once in a while, I wonder about something off the wall. Here's the latest:
If you were on a hypothetical stationary platform, very high above the earth (x number of miles), and you fired a gun downward, would the speed of the bullet eventually slow down to the velocity of gravity? Maybe "slow down" isn't the right term, maybe "match" the velocity of gravity would be a better term. 


#2
Mar1107, 01:00 AM

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What is the "velocity of gravity"? Gravity is a force. (in classical mechanics)
The speed of the bullet would eventually reach the terminal velocity with is the velocity where the force of airresistance on the bullet equals the force of gravity. If air resistance is R*V and gravity is Mg then R*V_terminal = Mg V_terminal = Mg/R Where R is some constant and M is the mass. 


#3
Mar1107, 12:02 PM

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#4
Mar1107, 12:14 PM

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Gravity Question... kind of



#5
Mar1107, 01:28 PM

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It is certainly true that if the bullet gets close enough to the Earth, the force it experiences from Earth will become approximately constant.



#6
Mar1107, 03:27 PM

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Well, I hope that helps. 


#7
Mar1107, 04:29 PM

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#8
Mar1107, 04:56 PM

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My previous post makes the assumption that the gun is initially a sufficient distance from the earth that the gravitational force is effectively zero. But the result holds true anyway. 


#9
Mar1107, 05:53 PM

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#10
Mar1107, 06:03 PM

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#11
Mar1107, 06:17 PM

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I dont understand the OP. what the question here



#12
Mar1107, 07:07 PM

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The ball thrown from a cliff is a much simpler situation.
If the initial velocity of the ball is greater then the terminal velocity, then the ball will slow down to the terminal velocity. If the initial speed of the ball is less then the terminal velocity it will accelerate at g until it reaches terminal velocity. In a vacuum, ie no air Resistance, the ball will accelerate at g. Its speed when it hits the ground will be the initial velocity plus the speed gained due to the acceleration of gravity. 


#13
Mar1507, 09:14 AM

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do u guys mean to say that a meteorite will hit at the terminal velocity...!!!
in this case the initial velocity is much much greater than terminal velocity... simply throw a piece of iron at a magnet with whatever force u can..when it hits the magnet obviously it will hit with a velocity more than if u had just let the magnet attract the iron piece by itself... 


#14
Mar1507, 09:23 AM

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If the atmosphere is thick enough and dense enough, relative to the initial speed of a meteoroid, the latter will indeed decelerate to its terminal speed. That is assuming that it doesn't just burn up as most do due to compression and friction heat. Keep in mind that they can be moving at over 100,000 mph relative to Earth, which introduces entirely different conditions than the OP was asking about.



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Mar1507, 12:11 PM

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#16
Mar1507, 12:14 PM

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#17
Mar1507, 12:50 PM

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moving in the direction away from earth g becomes smaller.
Doesn't the value of g becommes a little little bit bigger towards earth? Mayby it's a small effect, but is stil there. Also the gravity field strength of the object which is falling towards earth, is atrackting the earth itself. (but that is a really really small effect.) (is there an official name for a change in acceleration? I call it myself the escalation). Dimsun. 


#18
Mar1507, 03:18 PM

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