# B Question re. flying against Earth's rotation

1. Jul 20, 2016

### KhalBrogo

What would happen if an aircraft was fast enough to match the speed of the rotation of the earth and it decided to fly against it matching that exact speed (earth's rotation)?

I would imagine it would look like earth was speeding up but would there be any other physical effects on the aircraft? The passengers?

2. Jul 20, 2016

### drvrm

what do you think or expect to happen ?
The geostationary satellites actually match the speed of earth's rotation and the astronaut's experiences are well documented...weightless ness etc.

3. Jul 20, 2016

### Simon Bridge

The aircraft travelling over the surface of the earth at speed v just means that the scenery looks like it is going past at speed v.
It does not matter what that speed is (as long at it is well below the speed of light) or what direction you travel in.
Since the motion is circular, you do get pseudogravity effects and stresses on the airframe that depend on speed.
Maintaining the motion at a constant distance from the surface means the aircraft is not in freefall.

Note: the speed of the ground about the rotation axis depends on latitude, it can be quite slow.
You could go to someplace close to the north or south (rotation) pole and fly a model aircraft about and see what happens.
But it is quite easy to imagine.

4. Jul 20, 2016

### Delta Kilo

The Sun will not move in the sky and you arrive at the same local time as you depart.
I believe Concorde used to do that regularly on LHR-JFK route.

5. Jul 20, 2016

### A.T.

That is not the criterion of being in freefall, although the conclusion happens to be right in this case.

6. Jul 20, 2016

### Simon Bridge

Yes - I was not using that as the criterion but as an important detail, along with all the others, that can be used to inform an investigation.
To be pedantic: the question implies an aircraft flying as is usual for aircraft.
At the kinds of altitudes aircraft usually fly, the indicated speed does not suggest an orbit, yet the altitude is implied constant - therefore, gravity is not the only force on the aircraft vis: not free fall. Better?

Since this is circular motion we can expect centrifugal effects to be present ... but would we expect "weightlessness"?

7. Jul 20, 2016

### Staff: Mentor

No physical effects. Note: airplanes can do this. The rotation speed of Earth is about 1,000 mph at the equator and gets slower as you go further north/south. The Concorde went faster than that and military fighters do too.

8. Jul 20, 2016

### mrspeedybob

Wouldn't this rather be a lack of circular motion? Traveling with the earths surface would be circular motion, and i'd expect some centrifugal force to partially cancel out gravity, that's why the earth bulges at the equator. A plane flying against the rotation of the earth would not experience this force, so I'd expect the plane and passengers to weigh a bit more then they would at rest with respect to the surface.

9. Jul 20, 2016

### micromass

Go to the north or south pole and run in circles around it.

10. Jul 20, 2016

### A.T.

There is a small effect on fuel consumption, but it's negligible compared to air currents etc.

11. Jul 21, 2016

### nasu

It is not clear what situation you have in mind because you don't mention in what reference frame is the speed of the airplane considered.
But if you think about a situation where the airplane is stationary above a point on the Earth's surface there may be a problem.
As the atmosphere moves pretty much with the Earth, the airplane will be stationary in respect to the air so there will be not much lift to support the airplane.
Unless there is a strong wind blowing in the right direction.

12. Jul 21, 2016

### A.T.

Pretty sure not what he means.

13. Jul 21, 2016

### Staff: Mentor

0.3%. A good scale can measure this, but it is still a small effect. Go to the pole if you want to increase your weight even more (because you are also closer to the center of Earth there).

14. Jul 21, 2016

### Filip Larsen

The centrifugal component of the normal gravity changes (slightly) when travelling east or west, so everything else being equal there should be an effect, even if very minor. For instance, flying west on the equator with enough speed that the centrifugal term is zero should mean around 0.3% less weight and therefore less drag and less fuel consumption, again everything being equal.

15. Jul 21, 2016

### A.T.

http://naca.central.cranfield.ac.uk/reports/arc/rm/3680.pdf

16. Jul 21, 2016

### lychette

17. Jul 22, 2016

### hsdrop

Brian Cox hosts a show called: Forces of Nature
and in the 2 episode :Somewhere in Space-time he does just what you asked by getting into a jet and follows the sun till it comes back up throw the horizon its a really good watch if you can find it on the web

18. Jul 24, 2016

### sophiecentaur

You would need to be at the same height as a geostationary satellite for weightlessness with that particular angular velocity. (360° per 24 hours). Which is why the satellite is put at that particular height.

19. Jul 27, 2016

### Andrew Mason

As pointed out, there would be no centrifugal effect offsetting gravity so it be a bit heavier. If it was a rocket ship, it would also take a bit more fuel to get into orbit flying against the earth's rotation. I expect this is why rockets are launched west to east in low latitudes and why, for example, the Virgin Galactic plane flies west to east near the equator when launching its orbital vehicle into space.

AM

Last edited: Jul 27, 2016
20. Jul 27, 2016

### Drakkith

Staff Emeritus
They match the angular velocity of the Earth, but not the tangential velocity at the surface.