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Physics and Airtravel....

Alan Wanwierd
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Joined: Jun 30, 2004
Posts: 624
Just had a very frustrating conversation with my boss

He was trying to argue that air travel always takes longer when flying in a westerly direction due to the earths rotation...

I tried to persuade him that differing flight corridors and prevailing winds were a more likely explanation for the minor variances between Easterly and Westerly flights, but he remains unconvinced...

Can anyone give me a concise "aviation 4 dummies" explanation of why planetary rotation is insignificant? (The key, I'm guessing is in the question "Rotation relative to what?")
Thomas Paul
mister krabs
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Joined: May 05, 2000
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Ask your boss why the Earth doesn't speed out from under him when he jumps in the air. By his logic, helicopters should have great difficulty in hovering. But it's a cool idea... a helicopter could take off in NYC, hover for awhile, and then land in San Francisco. Cool!


Associate Instructor - Hofstra University
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Bert Bates
author
Sheriff

Joined: Oct 14, 2002
Posts: 8829
    
    5
I think you should get your boss going on the Monty Hall puzzle... you could fleece him


Spot false dilemmas now, ask me how!
(If you're not on the edge, you're taking up too much room.)
Nick George
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Joined: Apr 04, 2004
Posts: 815
lousy relativity...


I've heard it takes forever to grow a woman from the ground
Richard Hawkes
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Joined: Jan 28, 2003
Posts: 1340
Fact Attack !!

Taxi drivers live the longer than the rest of us. Why? Because they spend more of their time closer to the speed of light compared to those of us that sit at our desks all day.
Joel McNary
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Joined: Aug 20, 2001
Posts: 1821

...if anything, due to the Earth's rotation, then Westerly flights should take shorter, as the Earth rotates west-to-east.


Piscis Babelis est parvus, flavus, et hiridicus, et est probabiliter insolitissima raritas in toto mundo.
Warren Dew
blacksmith
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Joined: Mar 04, 2004
Posts: 1332
    
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Adrian Wallace:

He was trying to argue that air travel always takes longer when flying in a westerly direction due to the earths rotation...

I tried to persuade him that differing flight corridors and prevailing winds were a more likely explanation for the minor variances between Easterly and Westerly flights, but he remains unconvinced...


You could both be right. The prevailing winds are from the west in the temperate zones; that may make westward flights in that zone slightly slower than eastward flights. And the reason the prevailing winds are westerlies, rather than just southerlies, in the temperate zones is because of the coriolis effect, which results from the earth's rotation, so indirectly, he may be right too (except for flights that spend more of their time in the equatorial or polar regions).
Jeroen Wenting
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Joined: Oct 12, 2000
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The aircraft would indeed have a hard time catching up with the rotation of the earth were it not pulled along with it inside the earth's magnetic field.
As it is there may be some minute effect because of decreased gravitational pull at cruise altitude but that would not add more than a few seconds to a flight of several hours.

At 14000km diameter the earth rotates at about 1850kmh, the cruise speed of a jetliner is about 950kmh or half the speed of the earth itself.

According to the logic of your boss the aircraft would never be able to fly against the rotation of the earth and reach its destination in less than 24 hours...

Prevailing winds are indeed the true cause. Flight corridors are in fact designed to make maximum use of prevailing winds when flying east and minimise the slowdown when flying west.
Another factor (which is caused by those strong headwinds) is the fact that the aircraft needs to carry more fuel when flying west which means it cannot fly as high or fast as a lighter aircraft flying east.


42
Ray Marsh
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The atmosphere and everything in it rotates with the earth's surface.

In North America the jet stream travels West to East and flights take longer travelling west.

The earth's surface rotates at roughly 1,000 mph. If by becoming airborne the earth would rotate under you... well let's just say the world would be a much more interesting place to live!


Anxiety does not empty tomorrow of its sorrows, but only empties today of its strength. – Charles Spurgeon
fred rosenberger
lowercase baba
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While the plane is sitting on the ground, it is ALREADY MOVING at the same speed as the earth is rotating (otherwise it wouldn't be sitting, it'd be moving). Just because the plane leaves the surface doesn't mean it loses it's inertia - remember Newton's law?

Unless some force acts on it, it will keep moving around at the same speed. The plane is further from the surface, but only by a few miles, which is relatvily insignificant compared to the radius of the earth.

But like others have said, the winds ARE a force on the plane, that can effect the speed. That's why they talk about Airspeed and Groundspeed of a plane. A headwind will INCREASE your airspeed, but DECREASE your groundspeed. a tailwind does the opposite.


There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors
Matt Fielder
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Joined: Oct 27, 2004
Posts: 158
Originally posted by Jeroen Wenting:
[QB]The aircraft would indeed have a hard time catching up with the rotation of the earth were it not pulled along with it inside the earth's magnetic field.


Ummm. The Earth doesn't pull anything along via a magnetic field. We are all pulled to the center of the Earth. There's no magical magnet that stays slightly ahead of all metallic objects pulling them along.
John Smith
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Joined: Oct 08, 2001
Posts: 2937
JW: The aircraft would indeed have a hard time catching up with the rotation of the earth were it not pulled along with it inside the earth's magnetic field.

Ah, now I understand why the airplanes are made out of metal: were it any other non-magnetic material, you would never be able to fly in the same direction as the rotation of the Earth. In fact, since the Earth rotates with roughly twice the speed of a typical plane, you would be moving backwards relative to the point where you started from. And the helicopter made of non-magnetic material would be moving with the speed of about 1,000 mph just by staying up in the air.
Jerry Young
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Joined: Jun 15, 2004
Posts: 77
I also noticed this.

Let's do an ideal experiment --- imagine we put straight up an American flag along a 20K-meter long stick (or post?). I would imagine nonody can hold it on ground --- suppose the stick itself is zero mass and does not need any extra support to stand up there.

In high above there seems to always have strong wind.

One guess is this can be explained by earch's rotation. The air colse to ground may rotate at a diferent speed from the air high above; I guess it must because, suppose they rotate at the same "angle" speed, I mean, rotating a round in 1 day, they must have different "real" speed indeed.

But this seems not to be able to explain why the high air wind is so strong --- after all, they are only a few miles above, compared to the huge earth, it should have made no significant difference in the real rotating speed.

So maybe the Earch's rotation may have caused the high above air rotate at a different step than the Earth itself because of something else? For example, high airs straight above the diameter area and high airs straigt above polar areas may get different impact from Earth's rotation, i.e.e, they real have very different real speed actually, and because they are air --- fluid thing and NOT solid thing, they may start to squeeze each other, or one squeezes another, which forms strong winds.

Also another factor may be temperature --- diameter area air is always hotter than polar area airs, I suppose.

oops. I mean equator by saying "diameter"... English is my forever pain


[ November 24, 2004: Message edited by: Jimmy Chen ]
Thomas Paul
mister krabs
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It's the coriolis effect:

http://tinyurl.com/4dnex
Sonny Gill
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Posts: 1211

Originally posted by John Smith:

Ah, now I understand why the airplanes are made out of metal:


Aww...give him a break, magnetic field, gravitational field ..it is all the same mumbo jumbo anyway..

Good explanation though, Jeroen.
Joe King
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Joined: Sep 02, 2003
Posts: 820
Originally posted by Sonny Gill:

Aww...give him a break, magnetic field, gravitational field ..it is all the same mumbo jumbo anyway..


Magnetism is something I really don't understand. Several people on this forum have explained it to me, but I still don't get it - where does magnetism get the energy from to move stuff? Its pretty wierd, a bit like Gravity's strange cousin.
Jeroen Wenting
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Joined: Oct 12, 2000
Posts: 5093
Magnetism, gravitation, who cares
We call it the magnetic field here even if it's really a gravitational well...

As to where magnets get the energy: they don't.
A magnet exerts an energy field on its surrounding which interacts with other magnetic fields.
The fields will try to achieve a state of equilibrium. This can mean attraction or repulsion.
Certain materials will cause distortions in the field which act as a field of their own. This causes them to move towards the magnet (don't have the physics ready, it's been years since I did EM field calculations at university).

The energy is contained in the field itself.
Natural magnets will slowly loose their power over time, become demagnetised.
Electromagnets need to be constantly powered to maintain their field and the power consumption does indeed change if something moves through the field.

The earth's field is caused (probably, theories are changing over time) by the convective movement of magma flows in the earth's mantle, possibly combined with a metalic core.
Thomas Paul
mister krabs
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Joined: May 05, 2000
Posts: 13974
We call it the magnetic field here even if it's really a gravitational well...

And what plante would that be? The Earth has both gravity and magnetism. Since gravity is an attractive force and magnetism can be either attractive or repulsive, the two are not related. They are separate fundamental forces of nature. Gravity, electromagnetism, weak, and strong. Theories have united electromagnetism and the weak force.
Peter Rooke
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Joined: Oct 21, 2004
Posts: 804

Nice one - plane travel theory - maybe you should buy your boss The Illustrated Brief History of Time, [Stephen Hawking] for Xmas, I'll love to know what he makes of it

"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former." - Albert Einstein.


Regards Pete
Peter Rooke
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Joined: Oct 21, 2004
Posts: 804

This has just reminded me of the solution for our trains that never arrive on time. They have been allowed to increase the amount of time it takes between stations (ie run slower), and also run fewer services.

Adrian, maybe your boss could provide these train companies with some good excuses (earths rotation etc), when this solution fails.
Ray Marsh
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Joined: Jan 12, 2000
Posts: 458
Originally posted by John Smith:
...now I understand why the airplanes are made out of metal...


Most planes are made of aluminum or aluminum alloys... non-magnetic. fred rosenberger's explanation of inertia is the most concise and accurate answer to this question.
[ November 29, 2004: Message edited by: Ray Marsh ]
 
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