Airplane travel questions

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  • #26
A.T.
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Not a lot of help for sailors lol.
There would still be wind at the surface without rotation, just different patterns. Saying that using wind power (e.g. sailing) is "using the Earth's rotation" is IMHO misleading.

What is even more puzzling to me is your claim, that there would be wind without the sun, purely due to rotation. How would the combination of centrifugal and Coriolis forces produce winds?
 
  • #27
TumblingDice
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To 'hover' over a particular spot (over the equator, only) you would need a geostationary orbit which is 30,000+km.

That's not what the OP is about. It's about traveling from point A to point B. A geostationary orbit would go nowhere. OTOH, hovering while the Earth rotates below (what the OP asked about) is a relative view from the rocket's perspective. From the Earth POV, the rocket is traveling. So there's no need to 'hover' to gain advantage of Coriolis on a rocket path when the route provides for that. Just plot a straight line trajectory to where point B will have rotated to at end of flight.
 
  • #28
sophiecentaur
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There would still be wind at the surface without rotation, just different patterns. Saying that using wind power (e.g. sailing) is "using the Earth's rotation" is IMHO misleading.

What is even more puzzling to me is your claim, that there would be wind without the sun, purely due to rotation. How would the combination of centrifugal and Coriolis forces produce winds?

A fair question but my reasoning is to do with what goes on at extreme distances where 'orbital' forces start to be relevant. An object that's not going round above and parallel the equator will take up an orbit in a plane that's inclined to the equatorial plane. At an altitude well below the geostationary orbit, this would be a subtle effect as the g attraction is way more than the necessary centripetal force for a 24 hour orbit at a few hundred miles but there is still a finite effect. The same could reasonably be assumed to apply to air molecules. Doesn't this provide a reason for shear movements in the very low density layers? The orbital forces are not 'stratified' the same as the gravitational forces / air pressure. I might be convinced that some equilibrium situation could obtain but it looks to me that it is not an equilibrium situation.

Also, I was not implying (and definitely did not write) that sailing is using the Earth's rotation alone, just that the rotation / coriolis effect modifies the normal convectional (N-S) winds in a useful way. It increases the maximum wind speed and, usefully, causes the direction to vary so that you have a chance of going in any direction (as long as you are prepared to wait for a depression to shift.
 
  • #29
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Saying that using wind power (e.g. sailing) is "using the Earth's rotation" is IMHO misleading.

That was not said here. The question was "Is it possible to take advantage of Earth's rotation (about 1000 miles per hour) to travel from point A to point B?"

And the answer is definitely yes. Our aerial and sea routes do just that.
 
  • #30
A.T.
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A fair question but my reasoning is to do with what goes on at extreme distances where 'orbital' forces start to be relevant.
What are "orbital forces"? In the rotating rest frame of the planet there are:
Gravity + Centrifugal : a conservative field that adds no energy to the atmosphere
Coriolis : acts perpendicular to movement, so also adds no energy to the atmosphere

I see nothing in here that would prevent a static pressure distribution, with the atmosphere at rest w.r.t the planet.
 
  • #31
sophiecentaur
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So it would be sufficient for the atmosphere just to have an equatorial bulge? I guess I could buy that. I imagined that some other factor must be there. But the reference frame argument sort of clinches it.
 

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