Science Questions

Does the spin of the earth affect flights?

Tue, 3rd Sep 2013

Listen Now    Download as mp3 from the show Can a Person in a Bath Dehydrate?


Dave asked:

Does a flight take longer if the plane is flying against the spin of the earth?


Dominic - Well in fact, what's important is the plane’s speed relative to the AeroplaneEarth’s atmosphere – the air around it because that’s what's giving it its lift up into the air and that's what is providing the the friction which is meaning it's having to thrust to keep going forward. The Earth’s atmosphere is rotating with the surface of the Earth below it. The reason is, because it’s got friction with the land masses beneath it and that means the air is always being pulled to rotate with the Earth. So in fact, because the air above us is rotating at the same speed as the land below, and what matters is your air speed – your speed versus the air – it doesn’t matter whether you're going with or against the rotation of the Earth.

Dave - The one thing I would say with that is that there are some latitudes where the wind tends to blow in one direction. So, in our latitude, the prevailing winds from the west and they get even faster as you are higher up. So, it's a lot quicker to fly from the states to here than from us, back to the states. So, it’s actually quicker to go against the direction of the spin of the Earth than with it, it just happens to be the way the air is moving. Other places, the wind is in opposite directions and they’ll have the opposite effect.

Dominic - And I guess the other thing to say is that if you're going above the Earth’s atmosphere into space then satellites all do go from east to west because there, you're above the Earth’s atmosphere. You haven't got this drag from the air anymore and it is a lot easier to get into an orbit that goes with the Earth’s rotation rather than against it.

Chris - A little bit of drag though isn't there because the International Space Station and some of the lower flying satellites have to be boosted every so often because they are experiencing a little tiny bit of drag from wisps of atmosphere out there.

Dominic - That’s right. The International Space Station is in quite a low orbit, at about 130 or so kilometres up and it does have to thrust about once a month to maintain altitude.


Subscribe Free

Related Content


Make a comment

I think Dave question relates to the rotational speed of the earth on an object that is no longer on the surface of the earth, i.e suspended above the earth surface and it is a good question, if an object like the earth is travelling(spinning) at 1675 km/h or 465 meters/second then why wouldn't the travel time of an aircraft being affected. I guess the answer is the plane is still subject to the gravitation pull of the earth and is in fact rotating with it at the same speed (proportional to altitude) ,in much the same way ,that if you were to stand on a merry go round,you would be turning with it at the same relative speed, however you still can move in any direction at a normal speed but you are still rotating with it also. Tricky concept to visualize. tony mcdermott, Thu, 27th Feb 2014

one other comment is, Dominic commented that "The Earth’s atmosphere is rotating with the surface of the Earth below it. The reason is, because it’s got friction with the land masses beneath it and that means the air is always being pulled to rotate with the Earth."
Which is not correct the atmosphere is being acted on by earth's gravity in the same way ever other object is affected by gravity, and not due to frictional forces. If gravity had no affect on the atmosphere ,it would simply drift off into space tonyj18, Thu, 27th Feb 2014

Air navigation is a "simple" matter of vector addition. Wind is the velocity vector of air relative to the surface of the earth, and speed + heading is the velocity vector of the aircraft relative to the air immediately around it. Add the two together and you get the track vector which tells you how the aircraft is progressing relative to the ground. So if you are pointing west and flying at 400 kt, and the wind is blowing northwards at 300 kt, you will be travelling roughly west-north-west at 500 kt over the ground. The art of dead-reckoning navigation is to forecast the wind and offset your heading as required to maintain the desired track.

At some latitudes and high altitudes the wind vector does indeed relate directly to the spin of the earth, and the shift in wind direction with altitude, particularly at low levels, derives from the coriolis effect which determines how wind circulates around low-pressure areas.  If your airspeed is zero (a balloon or hovering helicopter) you will generally turn left as you descend. Landing an aeroplane on a windy day generally requires you to turn slightly right as you descend in order to stay on the runway centerline.      alancalverd, Fri, 28th Feb 2014

I agree that other objects like the GPS satellites (orbital period almost 12 hours), the Moon (orbital period about 4 weeks) or Jupiter (not orbiting Earth at all) are affected by gravity in the same way as the atmosphere.

The difference is that objects like my house (precisely 1 rotation per 24 hours) or the atmosphere (very close to 1 rotation per 24 hours, on average) have an additional and dominant force operating on them: Friction with the Earth's surface (1 rotation every 24 hours).

If it was primarily gravity determining the rotational period, my house and the atmosphere would rotate around the Earth slightly faster than the International Space Station, in 90 minutes. evan_au, Sun, 2nd Mar 2014

If you can catch a jet stream it can give substantial speed/fuel savings.  Apparently they flow in the direction of earth's rotation and are caused by the moving heat/cool cycles caused by the movement of the day/night cycles.

There is also the time change.  So, flying from the USA to Europe often is a 24 hour flight, whereas flying from Europe to the USA, one can leave in the morning and arrive in the evening. CliffordK, Sun, 2nd Mar 2014

Flying from Sydney to Los Angeles, you arrive before you left (according to the local clocks)! (...who says time travel is impossible or just unlikely?)

But you skip a day on the way back. evan_au, Sun, 2nd Mar 2014

Only for civilians. Sensible people use UTC, so the time is the same everywhere and the westward flight takes about 20 - 60 minutes longer depending on your track relative to the jet stream. alancalverd, Sun, 2nd Mar 2014

The GPS satellites, Moon and space station will take different times to rotate the earth due to their relative distance from the centre of the earth, simply because the further away their are the greater distance they have to travel around the earth.
This also applies to the different layers making up our atmosphere.
Gravity exerts the same force on all known objects that we are aware of, friction always opposes the motion or attempted motion of one surface across another surface, your house is not opposing the surface of the earth it is moving with it, in the same way the atmosphere moves with the rotation of the earth.
This is separate to jet stream affects or other weather affects, these are indeed due to heating and cooling of the air.
"thedoc"'s question was in reference to the spinning of the earth and how it affects a plane flying across the earth surface. tonyj18, Sun, 2nd Mar 2014

Well, the air 'moving' with Earth must always be slightly behind Earths spin, doesn't it?  And then we have gravitational frame dragging to consider too :) yor_on, Tue, 4th Mar 2014

no it moves at the same speed as the earths rotation, there would be no lag time, but there are still influences from wind etc. ,similar to the oceans ,they also move with the earth rotation, but they still are also influenced by ocean currents (heating and cooling). tonyj18, Tue, 4th Mar 2014

Yep, but think of it all as originally being still. Then start to rotate that Earth. The atmosphere gets its angular momentum through friction primarily, right? So even when getting up to speed, it will be slightly behind the position it had before we started to rotate that Earth :) I'm sure we can have us some good arguing here.. yor_on, Wed, 5th Mar 2014

even if the atmosphere was moving along with the earth the plane would be being blown sideways in a north/south flight as it went from a pole towards the equator... there are things called, drag... friction... a gas would in no way rotate along with or ever catch up with a solid... ever. even in a vacuum it would SPIRAL. The air resists ITSELF... it is a gas..... a gas.. FRICTION... RESISTANCE... to ITSELF ffs.. It is absolutely impossible for the atmosphere to be held on by gravity. the force of a butterflies wings can overcome gravity... now try the force of 1000mph plus 17.6 miles PER SECOND around the sun (alleged) and 500,000 mph around the galaxy.... We would all be dead LOOOOONG ago. The earth is a big cave. about 25000 miles in circumference. We are on the inside. Measure it yourself at any ocean or river... I have... so have many others... Trip on that. Cyrus, Tue, 31st Mar 2015

Your are wrong International Space Station ( ISS ) is not at 130 Km or so, it is exactly at 400km. Sam, Mon, 27th Apr 2015

Your are wrong International Space Station ( ISS ) is not at 130 Km or so, it is exactly at 400km. Sam, Mon, 27th Apr 2015

yeah just one small issue ... RESISTANCE... Solid objects are made of molecules that travel in straight lines when they spin. A gas is made of molecules that do NOT follow straight lines as they 'spin'. a gas RESISTS ITSELF. Whereas a solid does NOT. aka. eg. ie. ipso facto - Solid wins the spin race... everytime... If the Earth were spinning at the alleged 1000mph... there would be constant spiraling as you rose in altitude as the higher altitude air would slow down from resisting itself. Like how galaxies form allegedly. as you went from the north pole to the equator you would encounter an ever increasing side wind until it reached 1000mph. And then the point that if the Earth were moving through space at all then again the solid matter would travel in straight paths while the gasses tumbled and resisted themselves right on off the 'planet' with far greater force than a butterflies wings which is all a gas needs to defeat the force of gravity... If you go outside and feel the Earth spinning... go see your doctor... Prove that it does spin and you will be the first person in history to do so. NASA is not a credible source for this thought experiment. Rely on your OWN BRAIN and evidence and prove that it spins. Whereas the Allais effect, Michleson-Morley, Airy's Failure, Tamarack mines, The Rectiliniator, and choads of other easy to repeat experiments... prove... that a lot of people are way more arrogant about what they have been brainwashed to believe than they are willing to look at repeatable, provable, evidence acquired by scientific method. Remove trust from the equation and reevaluate it. For a minute only consider the evidence and not the source. If you can... it is hard for a pack of wild animals i do understand... John, Thu, 14th May 2015

What is John talking about?? Graham, Wed, 2nd Dec 2015

if the atmosphere were spinning with the earth, and the earth only spins in a certain direction, why would then have winds blowing in every direction, this way now and then the other? If the earth were dragging an airborne aeroplane with it via gravity, then necessarily the plane will need more power output in order to achieve similar speeds when travelling westward as eastward. the total absence of any discrepancies in these values (can be confirmed with any seasoned and clear-headed pilot) is a damning evidence against the earth's rotation. Jimi, Thu, 28th Jan 2016

See the whole discussion | Make a comment

Not working please enable javascript
Powered by UKfast
Genetics Society