Does it draw a line?
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From: Brit in Athens, Greece
Originally Posted by starchland,Oct 2 2009, 11:20 PM
turbulence
tink, here's my take on the 'moving backwards, since it's no longer 'connected' to the earth' thing...
Imagine a spinning planet, in space, with no atmosphere. A hovercraft sitting ON it, lifts off and hovers. It is now effectively in stationary orbit of the planet, albeit at an altitude of 1ft. Does it slow down? I maintain that it doesn't. Since there is no wind resistance, it will maintain orbit like any other stationary satellite.
Now, on Earth we have atmosphere, but that atmosphere is also under the influence of the earths gravity, it is effectively standing still (or rather it is also in a stationary orbit), it's only the actions of the seas and seasons that make it move around the surface. If we're talking about a theoretical atmosphere that doesn't have wind or otherwise affect the hovercraft, then again the hovercraft stays still. If we're talking about an atmosphere in which winds are blowing, then obviously the hovercraft will be moved by the winds, independent of any rotation of the planet.
That make sense to you?
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Originally Posted by foxy_s2k,Oct 3 2009, 06:15 AM
tink, here's my take on the 'moving backwards, since it's no longer 'connected' to the earth' thing...
Imagine a spinning planet, in space, with no atmosphere. A hovercraft sitting ON it, lifts off and hovers. It is now effectively in stationary orbit of the planet, albeit at an altitude of 1ft. Does it slow down? I maintain that it doesn't. Since there is no wind resistance, it will maintain orbit like any other stationary satellite.
Imagine a spinning planet, in space, with no atmosphere. A hovercraft sitting ON it, lifts off and hovers. It is now effectively in stationary orbit of the planet, albeit at an altitude of 1ft. Does it slow down? I maintain that it doesn't. Since there is no wind resistance, it will maintain orbit like any other stationary satellite.
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Originally Posted by foxy_s2k,Oct 3 2009, 07:15 AM
That make sense to you?
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From: Brit in Athens, Greece
Originally Posted by Elistan,Oct 3 2009, 06:15 PM
Yes, but now the hovercraft has to go FURTHER than the planetary surface in order to complete a full rotation, yet is only going as fast as the surface. Therefore once the surface completes a full rotation, the hovercraft still has some extra distance to go, and therefore has fallen behind.
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From: Brit in Athens, Greece
Originally Posted by Schoolloans,Oct 4 2009, 02:15 AM
Jesus man.
Of course if you jump, you're traveling at the same speed of the earth's rotation. As is the atmosphere (at least to some extent). So you'll land at the same point. Needless to say, your hangtime is not nearly enough to have you slow down (if you would at all) to land in a different spot. Such a bold answer without any thought behind it.
Toss a tennis ball up when you're driving, it will fall back into your hand. That's NOT THE SAME as a tennis ball hovering somewhere for a sustained period of time.
My vote: The atmosphere is moving very close to the earth's rotational speed, especially at lower altitudes (hence weather STAYS relatively to an area).
I'd imagine the rotation of the atmosphere must slow as you get higher.
So, perhaps a hovercraft, extremely high, given enough time will of course draw a line.
Of course if you jump, you're traveling at the same speed of the earth's rotation. As is the atmosphere (at least to some extent). So you'll land at the same point. Needless to say, your hangtime is not nearly enough to have you slow down (if you would at all) to land in a different spot. Such a bold answer without any thought behind it.
Toss a tennis ball up when you're driving, it will fall back into your hand. That's NOT THE SAME as a tennis ball hovering somewhere for a sustained period of time.
My vote: The atmosphere is moving very close to the earth's rotational speed, especially at lower altitudes (hence weather STAYS relatively to an area).
I'd imagine the rotation of the atmosphere must slow as you get higher.
So, perhaps a hovercraft, extremely high, given enough time will of course draw a line.
Take atmosphere out of the equation and your hovercraft is maintaining a stationary orbit at an altitude of 1ft. With no force acting on it, it will stand on the spot like any object in stationary orbit of a planet, at any altitude.
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Originally Posted by foxy_s2k,Oct 4 2009, 01:14 AM
No it won't. You're tennis ball example is 100% valid and correct. You have to take 'atmosphere' out of the equation, otherwise you have to say 'of course it draws a line as it is buffeted by our atmosphere (the wind)'. That's not helpful for our original, theoretical premise that the inertia of the rotation of the earth is reduced once you leave contact with the ground. It most definitely is not.
Take atmosphere out of the equation and your hovercraft is maintaining a stationary orbit at an altitude of 1ft. With no force acting on it, it will stand on the spot like any object in stationary orbit of a planet, at any altitude.
Take atmosphere out of the equation and your hovercraft is maintaining a stationary orbit at an altitude of 1ft. With no force acting on it, it will stand on the spot like any object in stationary orbit of a planet, at any altitude.
Putting this into a vac. is not the spirit of the original post. We want to know if the speed of the craft is reduced when you leave. Clearly with no atmosphere, it isn't. There's nothing to slow the hovercraft down. No shit. Now, leave the atmosphere in. But take out wind, and just ponder the fact that the atmosphere is moving at least somewhat with the earth's rototation. Put forth your best answer with those facts.
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From: Brit in Athens, Greece
A theoretical atmosphere is also in stationary orbit, or considered to be in contact with the ground. Therefore irrelevant.
Here's another example for you. Take the atmosphereless planet once again... Put the hovercraft on the ground. Make a bubble round the hovercraft filled with 'air'. Repeat the experiement. Again the hovercraft and the artificial atmosphere are in a stationary orbit, again the hovercraft will not move.
Here's another example for you. Take the atmosphereless planet once again... Put the hovercraft on the ground. Make a bubble round the hovercraft filled with 'air'. Repeat the experiement. Again the hovercraft and the artificial atmosphere are in a stationary orbit, again the hovercraft will not move.
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From: Wylie, TX
Originally Posted by foxy_s2k,Oct 4 2009, 04:12 AM
If that were the case, satellites in stationary orbit would eventually fall out of the sky. What force is acting on it to slow it down? Simply changing elevation, but remaining in the planet's gravitational field, it should not slow down (or move backwards).
http://en.wikipedia.org/wiki/Geostationary_orbit
http://imagine.gsfc.nasa.gov/docs/ask_astr...rs/970401c.html
From those two links you can see that the circumference of the earth is 40,075km (24901mi) and a geostationary satellite's orbit is 265000km (164650mi). However, they both travel that distance in 23hr 56min. That means that the surface of the earth (at the equator) is moving about 1040mph and the geostationary satellite is moving about 6860mph.
That information also supports my previous answer, since a hovercraft is propelled directly upwards (with no lateral velocity) and it now has a larger "orbit" than the surface of the earth, so it will slowly fall behind the point from which it originated.