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Author Topic: If I shoot A Bullet straight Up From The Moon Will It Fall Back ?  (Read 5701 times)

Offline neilep

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Dearest Moon-Bulletologists,


As a sheepy, I of course (like Charlton Heston) just luff owning guns....In fact, the first thing I do every single day is shoot a bullet through some crayons ! yep, as soon as I open my eyes it's fast-draw sheepy and bang goes the crayons !!


see?


Me Shooting Bullets Through Some Crayons


However, As an Astro-sheep in training........ I also have a desire to shoot a bullet vertically straight up from the moon. I am curious though. Will my bullet continue on it's way to cosmos joy or will it eventually come back down to moon ?...and will it fall back into the same exact spot that it was fired from ?..after all there's no atmosphere  eh ?...Will it fall back backwards too ?


As a firm believer in empirical study I (left my neighbour alone) and hired a taxi to drop me off on the moon where I attempted my experiment..!!..



A Bona Fide Image Of Me On The Moon Shooting My Load !



Unfortunately I forgot that all I had were blanks !!..D'OH !!...so..no luck there.



Hoping ewe can help me with this bullet-orientated-vertically-firing-outer-space-moon-dwelling question !


Hugs & Shmishes



mwah mwah mwah mwah !!




neil
Astro-Sheep Residing On The Moon
Yes quite Sane & Not A Loon !
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx


 

Offline syhprum

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Assuming that you fire the bullet vertical ie at 90° to the tangent of the surface and it is a pistol of normal power so that it moves at less than escape velocity (2.38 km/s)it will fall back quite close to where it started but of course some allowence must be made for the fact that the moon is rotating at .0086°/s.
There is only a 50/50 chance that it will fall back base first some spin and randomness will inevitably be imparted to it
 

Offline Geezer

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Better wear a steel helmet too. When the bullet comes back to earth moon, because there is no atmosphere to slow it down, it will be travelling as fast as it was when it left the barrel of your Glock.
 

Offline neilep

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Assuming that you fire the bullet vertical ie at 90° to the tangent of the surface and it is a pistol of normal power so that it moves at less than escape velocity (2.38 km/s)it will fall back quite close to where it started but of course some allowence must be made for the fact that the moon is rotating at .0086°/s.
There is only a 50/50 chance that it will fall back base first some spin and randomness will inevitably be imparted to it

THANK EWE very much syhprum.  So, a crash helmet is advised...or perhaps I just need to step a few feet away.

If the moon was not rotating, I imagine then, it would indeed fall back in the exact same space. I'll be very careful.

Thanks again
 

Offline neilep

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Better wear a steel helmet too. When the bullet comes back to earth moon, because there is no atmosphere to slow it down, it will be travelling as fast as it was when it left the barrel of your Glock.

A steel helmet has been ordered via bulletproofspacehelmets.com. Thanks Geezer.

will it really fall back at the same speed ?  how come ?..cos won't it eventually come to a halt and then slowly start to fall back ?....how does the original shooting speed affect this ?....ahhh..I think I might have just guesssed it myself...is it because of the height the bullet travels ?
 

Offline Geezer

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Better wear a steel helmet too. When the bullet comes back to earth moon, because there is no atmosphere to slow it down, it will be travelling as fast as it was when it left the barrel of your Glock.

A steel helmet has been ordered via bulletproofspacehelmets.com. Thanks Geezer.

will it really fall back at the same speed ?  how come ?..cos won't it eventually come to a halt and then slowly start to fall back ?....how does the original shooting speed affect this ?....ahhh..I think I might have just guesssed it myself...is it because of the height the bullet travels ?

Yup. You probably figured it out. After the bullet leaves the gun it decelerates because of the moon's gravity. As it slows down it loses kinetic energy, but it is gaining potential energy. It eventually stops, at which point it has maximum potential energy and zero kinetic energy.

Then the process reverses and all the potential energy is converted back into kinetic energy as the bullet accelerates back towards the surface of the moon. As there is no energy loss, it accelerates back to the initial velocity (in the opposite direction of course) when it left the gun barrel.

The same would not be true on earth because the bullet would lose energy as it heated the atmosphere due to friction both on the way up, and on the way back down, so the return velocity will be quite a bit less than the muzzle exit velocity.

If you aimed the gun horizontal, and the muzzle velocity was sufficiently great, the bullet would orbit the moon and come back and hit you in the butt (assuming it didn't collide with a mountain en route). Someone might care to calculate the required muzzle exit velocity to achieve this remarkable feat. Actually, if it missed your butt the first time around, it might get you on the second etc. It would eventually stop orbiting because there is some energy transfer from the bullet to the moon due to gravity.
« Last Edit: 04/10/2009 17:01:24 by Geezer »
 

Offline syhprum

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The figure I quoted for the Moons rotation is of course an average one its rotation is more complex due to its close association with the more massive Earth it takes an epicycloid form being in the reverse direction at times.
If I had the appropriate skills I could plot a three dimensional probability graph of where the bullets will fall (a job for Mathmetica ?)
 
« Last Edit: 09/10/2009 11:07:33 by syhprum »
 

Offline yor_on

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Nice one :)
 

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