What goes up must come down

Tell stories about your spud cannon adventures!

Postby clide » Sun Jan 15, 2006 9:51 pm

Air resistance does slow it down, but not in any relation to the motion of the earth.

Thinking about it again I suppose the earth would move under it some, but its still not any significant amount. It would be the difference of the the speed needed to keep up with the earth a a certain height compared to what the surface speed actually is. I don't know how you would go about doing all the way up and all the way down, but say you shot a projectile strait up at the equator and for our purposes we will say it instantly goes up 1 km and hangs there for 10 seconds and instantly comes back down, it would land .73 m away according to my calculations. An amount that could easily be made up by a little wind or being a TINY amount off from vertical. So for our purposes I would still say the spud would come strait down.

Edit: Fixed a number
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Postby Lord of the Rings Junkie » Sun Jan 15, 2006 10:24 pm

Heh, a story is turning into a physics discussion...:D It's interesting to see how these things evolve.
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Postby fullmetaljacket » Mon Jan 16, 2006 1:28 am

As Plow said, this notion of the earth turning faster than the projectile is something that is taken into account when calculating artillery trajectories, it's not something I plucked out of my arse'ole.

The atmosphere might be rotating as well, but it's not fixed to the earth's surface, so it tends to "slip" - besides, even if it were rotating at the same speed, it cannot push on the projectile in the same manner that the earth does when it is in contact with it.
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Postby clide » Mon Jan 16, 2006 2:01 am

Yes it will move under the projectile, but it has nothing to do with the atmosphere, just a difference in rotational velocity due to height. Why would the atmosphere "slip"? AFAIK there is nothing trying to stop it from rotating at the same speed as the earth.
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Postby SMOMW » Mon Jan 16, 2006 2:07 am

Ok... as the projectile moves up its rotational velocity would have to INCREASE to match speed with the point at which it left the ground.. but for our situations the distance the spud travels upwards doesn't cause much difference and makes it seem like it's just going strait up.

hmmm...okay....
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Postby orangekid13 » Mon Jan 16, 2006 4:02 am

people are thinking too accurately... there are no conditions in which we can throw something far enough in the air without it's shape, the density of the air, wind, humidity, birds, kites, and whatnot getting factored in and have the earth rotating be able to be detected in its path... considering that the runway that NASA lands the shuttles on is HOW MANY MILES LONG and only off 2-3" in altitude over the course of the ENTIRE THING so that it's perfectly flat (flat, not constant altitude) there will never be a spud that can survive the force it would take to lauch it that hard, to go that far, muchless the trip up and down...

any questions?
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Postby benstern » Mon Jan 16, 2006 12:15 pm

next time you go on a plane, jump up.. you will land a few inches from where you started AND annoy the other passengers!
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Postby Lord of the Rings Junkie » Mon Jan 16, 2006 12:48 pm

If we add a conveyor belt...;)
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Postby clide » Mon Jan 16, 2006 2:13 pm

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by benstern
[br]next time you go on a plane, jump up.. you will land a few inches from where you started AND annoy the other passengers!
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

Only if the plane is accelerating, or you're unable to jump strait.

Oh, and thank you orange. Unless you have a gun that can shoot several miles into the air, can measure the wind at all altitudes of flight, adjust the gun within a few hundredths of a degree or more, have a very consistent muzzle velocity, need to hit a fairly small target, and a program capable of making the calculations needed, then regarding the earth as still would not cause you any problems.
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Postby fullmetaljacket » Mon Jan 16, 2006 3:09 pm

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by clide</i>
Unless you have a gun that can shoot several miles into the air, can measure the wind at all altitudes of flight, adjust the gun within a few hundredths of a degree or more, have a very consistent muzzle velocity, need to hit a fairly small target, and a program capable of making the calculations needed, then regarding the earth as still would not cause you any problems.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

I agree, but what I was trying to point out was the extreme unlikelyhood of a projectile shot straight landing back on the spot where it was launched.
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