Airplane travel questions

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Hi,

Can someone please help me understand these two situations?

1. When an airplane is flying from point A to point B, is Earth stationary from the point of view of the plane? While I am not sure, I think the answer to this question is yes, because a plane flies within the atmosphere of Earth and these atmospheric layers must be rotating at the same speed as Earth. Is that correct?

2. Is it possible to take advantage of Earth's rotation (about 1000 miles per hour) to travel from point A to point B? Why can't we create a rocketship that launches from point A on Earth, goes into the outer space in a straight line, stays there until point B is underneath it (due to earth's rotation) and then comes down?

Thanks.
 

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  • #2
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1. When an airplane is flying from point A to point B, is Earth stationary from the point of view of the plane?
Yes, for the reasons you stated.
2. Is it possible to take advantage of Earth's rotation (about 1000 miles per hour) to travel from point A to point B? Why can't we create a rocketship that launches from point A on Earth, goes into the outer space in a straight line, stays there until point B is underneath it (due to earth's rotation) and then comes down?
We cannot, because the rocket will have the motion of the Earth as you launch it. In fact, this is used to advantage in getting payloads into orbit - they are usually launched to the east, so that the velocity of Earth's rotation adds to the velocity produced by the rocket.
 
  • #3
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Answer may apply to older problem. Heavy planes (like the raid on Tokyo WWII) could take off from aircraft carriers because the speed of the ship was added to the speed of the plane. I think that's similar.
 
  • #4
russ_watters
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1. When an airplane is flying from point A to point B, is Earth stationary from the point of view of the plane?
"Stationary" is a pretty arbitrary concept; We get to decide what we want to call "stationary". For simplicity, when we are sitting on earth we call that "stationary". When we leave earth in a plane, we change our frame of reference, but the earth-centered frame we leave is still "stationary".
 
  • #5
AlephZero
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If you want to navigate to a specific destination point, the easiest way to do that is work relative to the earth, which is the same as pretending the earth is "stationary".

Since the atmosphere rotates at approximately the same speed as the earth (apart from the wind speed which is usually much less than 1000 mph), and the aerodynamics of the plane is relative to the air it is flying through, again that gives no reason NOT to measure things relative to the earth. Of course that does not apply to space travel outside the atmosphere.

Heavy planes (like the raid on Tokyo WWII) could take off from aircraft carriers because the speed of the ship was added to the speed of the plane.
That's not quite right. You sail the carrier into the wind, to maximize the wind speed over the flight deck and therefore create the lowest takeoff speed and landing speed relative to the ship, not relative to the earth (or sea).
 
  • #6
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We cannot, because the rocket will have the motion of the Earth as you launch it. In fact, this is used to advantage in getting payloads into orbit - they are usually launched to the east, so that the velocity of Earth's rotation adds to the velocity produced by the rocket.

Okay. Is the direction in which the rocket goes that important? As long as we are able to get out of earth's atmosphere and hover at one point for some time and come back in when the specific point on earth is nearby, it should work, right?
 
  • #7
SteamKing
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Okay. Is the direction in which the rocket goes that important? As long as we are able to get out of earth's atmosphere and hover at one point for some time and come back in when the specific point on earth is nearby, it should work, right?

Yes, it's vitally important. Rockets are launched in an easterly direction, since that is the direction in which the earth rotates. As a result, the velocity the rocket requires to achieve orbit is reduced somewhat. If rockets were launched in a westerly direction, this velocity reduction would not be available, and the rocket would in fact have to achieve a greater velocity to enter orbit.
 
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  • #8
adjacent
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the velocity the rocket requires to achieve orbit is reduced somewhat.
No.It is not.The velocity required is same but the velocity WE give to the rocket is reduced somewhat.
 
  • #9
TumblingDice
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Why can't we create a rocketship that launches from point A on Earth, goes into the outer space in a straight line, stays there until point B is underneath it (due to earth's rotation) and then comes down?

Okay. Is the direction in which the rocket goes that important?

It would be, if you have a definite destination in mind. (point B)

Yes, it's vitally important. Rockets are launched in an easterly direction, since that is the direction in which the earth rotates. As a result, the velocity the rocket requires to achieve orbit is reduced somewhat. If rockets were launched in a westerly direction, this velocity reduction would not be available, and the rocket would in fact have to achieve a greater velocity to enter orbit.

But OP isn't about orbit. Question was about going in a straight line and coming down at point B. Everything except the "stays there until point B" part is reasonably accomplished. Launching to the east is only beneficial for reaching latitudinal orbit. Here in the U.S., all polar orbit launches originate at Vandenberg AFB (California) and launched westerly.

So a rocket can benefit from 'least distance' flight path just as well as airplanes benefit from flying polar routes. This may not be exactly what the OP was expecting, but keeps in the spirit of the exercise.
 
  • #10
adjacent
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It would be, if you have a definite destination in mind. (point B)



But OP isn't about orbit. Question was about going in a straight line and coming down at point B. Everything except the "stays there until point B" part is reasonably accomplished. Launching to the east is only beneficial for reaching latitudinal orbit. Here in the U.S., all polar orbit launches originate at Vandenberg AFB (California) and launched westerly.

So a rocket can benefit from 'least distance' flight path just as well as airplanes benefit from flying polar routes. This may not be exactly what the OP was expecting, but keeps in the spirit of the exercise.
The OP was talking about launching a rocket up at point B and stay there until earth rotates and B is below the rocket.I think this is more expensive and risky than just an aeroplane travelling.
 
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  • #11
TumblingDice
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The OP was talking about launching a rocket up at point B and stay there until earth rotates and B is below the rocket.I think this is more expensive and risky than just an aeroplane travelling.

I think expense and risk are eclipsed by the "how" are you going to "stay there". That's why I mentioned that as the exception. However the rocket can be launched in a straight line, and it does have a 'zero moment' at the peak of its trajectory, and it can leverage the Coriolis effect to take advantage of Earth's rotational speed.

Any advantage, of course, would depend on points A and B. E.g., you could never get rotational advantage traveling from the north pole to the south pole.
 
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  • #12
A.T.
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When an airplane is flying from point A to point B, is Earth stationary from the point of view of the plane?
Of course not. How would the plane get from A to B, if there was no relative movement between plane and Earth?


Is it possible to take advantage of Earth's rotation (about 1000 miles per hour) to travel from point A to point B?
Yes, if you travel fast enough relative to Earth, there is a apparent weight reduction, so you save some fuel. But the effect is negligible and when you fly back the same way, it is reversed. See Fig. 5 of this paper:
http://naca.central.cranfield.ac.uk/reports/arc/rm/3680.pdf
 
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  • #13
sophiecentaur
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Okay. Is the direction in which the rocket goes that important? As long as we are able to get out of earth's atmosphere and hover at one point for some time and come back in when the specific point on earth is nearby, it should work, right?

How did you envisage doing that? To stay up there you need to be in an orbit or use an unthinkable amount of energy. To 'hover' over a particular spot (over the equator, only) you would need a geostationary orbit which is 30,000+km.
 
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  • #14
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Thanks folks.
How did you envisage doing that? To stay up there you need to be in an orbit or use an unthinkable amount of energy. To 'hover' over a particular spot (over the equator, only) you would need a geostationary orbit which is 30,000+km.

Hmm...I didn't think about this. Now it is clear to me. Thanks a lot folks.
 
  • #15
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2. Is it possible to take advantage of Earth's rotation (about 1000 miles per hour) to travel from point A to point B?

Yes, and this has been done for centuries, if not millennia. Google "trade winds".

Today, this is seen in airline timetables: flights from North America to Europe are about one hour shorter than the other way around.
 
  • #16
sophiecentaur
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Everyone who sails a boat is making use of the Earth's rotation, too. It's the Coriolis force that provides the high speed winds in the vortices we call depressions and cyclones.
 
  • #17
A.T.
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Everyone who sails a boat is making use of the Earth's rotation, too. It's the Coriolis force that provides the high speed winds in the vortices we call depressions and cyclones.
It's not like there would be less wind, if the Earth didn't rotate. At high altitudes it would probably be even faster.
 
  • #18
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Everyone who sails a boat is making use of the Earth's rotation, too. It's the Coriolis force that provides the high speed winds in the vortices we call depressions and cyclones.

The Coriolis doesn't produce any winds. The Coriolis force is always perpendicular to the direction of motion of the wind so it does no work. It's the pressure gradient force that does the work on the atmosphere that produces the winds.
 
  • #19
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It's not like there would be less wind, if the Earth didn't rotate. At high altitudes it would probably be even faster.

Would they still have a longitudinal component?

The Coriolis doesn't produce any winds. The Coriolis force is always perpendicular to the direction of motion of the wind so it does no work. It's the pressure gradient force that does the work on the atmosphere that produces the winds.

Explain how the pressure gradient makes the Clipper Route possible.
 
  • #20
sophiecentaur
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The Coriolis doesn't produce any winds. The Coriolis force is always perpendicular to the direction of motion of the wind so it does no work. It's the pressure gradient force that does the work on the atmosphere that produces the winds.

You didn't read what I wrote. The coriolis force introduces vortices into what would be smoother flowing convection currents. Depressions are there because of the coriolis force. When vortices are introduced into a smooth flowing fluid, we find regions of higher (and regions of lower) speeds. That's why designers of planes, boats, cars and turbines try to suppress the formation of vortices.

Aamof, I am pretty sure that a spinning planet with an atmosphere but no source of radiation (a nonsense scenario, I know, as any fluid would freeze) would still have circulating currents and shear movements in its upper atmosphere. These would end up affecting the whole atmosphere and the combination of centrifugal and coriolis forces would be producing winds.
 
  • #21
A.T.
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It's not like there would be less wind, if the Earth didn't rotate. At high altitudes it would probably be even faster.
Would they still have a longitudinal component?
Define "longitudinal" for a non spinning planet.
 
  • #22
A.T.
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I am pretty sure that a spinning planet with an atmosphere but no source of radiation (a nonsense scenario, I know, as any fluid would freeze) would still have circulating currents and shear movements in its upper atmosphere. These would end up affecting the whole atmosphere and the combination of centrifugal and coriolis forces would be producing winds.
What would drive those circulating currents and shear movements in its upper atmosphere?
 
  • #23
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Define "longitudinal" for a non spinning planet.

If the planet has no spin "about itself", it is still revolving about its Sun. So the straight line through the center of the planet orthogonal to the orbital plane can be considered the North-South line, and everything else follows.

But that answers my question, I think. The part of the planet facing the Sun would be hottest at the spot closest to the Sun, which should generate an upward stream there, with colder air drawn from all the directions radial to that spot, so, yes, that would have "longitudinal" components except at the poles. But the pattern of prevailing winds will be markedly different, and, locally, it would change significantly in the course of the year.
 
  • #24
sophiecentaur
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It's not like there would be less wind, if the Earth didn't rotate. At high altitudes it would probably be even faster.

Not a lot of help for sailors lol.
 
  • #25
sophiecentaur
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This thread has done an interesting morph from the OP content.

But for the rotation of the planet, the weather would be pretty much predictable with massive extremes of temperature (viz Mercury) and, with a 365 (366?) day 'day', evolution would have taken us down a very different route. There would, of course, have to be no moon or that would have got us spinning, albeit rather slowly.
 

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