A question I'm embarrased to ask - earth's spin

I was talking about Coriolis effect with someone and he asked me about
planes against or with the earth's spin of around 1000mph at the equator. He
asked why this didn't benefit east to west plane travel timewise and hurt
west to east. I couldn't give him a straight answer, and felt like an idiot
when I said "it just doesn't".

What IS the straight answer? The dropping something in a moving vehicle
analogy doesn't work, does it? A plane has a method of acceleration, whereas
a passively dropped object doesn't.

Sometimes really simple questions can give you the worst time.

xerj wrote:
I was talking about Coriolis effect with someone and he asked me about
planes against or with the earth's spin of around 1000mph at the equator. He
asked why this didn't benefit east to west plane travel timewise and hurt
west to east. I couldn't give him a straight answer, and felt like an idiot
when I said "it just doesn't".

What IS the straight answer? The dropping something in a moving vehicle
analogy doesn't work, does it? A plane has a method of acceleration, whereas
a passively dropped object doesn't.

Sometimes really simple questions can give you the worst time.

Because when you leave the earth you are traveling the same relative
speed as the earth as is the atmosphere in which you are traveling.

Matt

In article ,
"xerj" wrote:

I was talking about Coriolis effect with someone and he asked me about
planes against or with the earth's spin of around 1000mph at the equator. He
asked why this didn't benefit east to west plane travel timewise and hurt
west to east. I couldn't give him a straight answer, and felt like an idiot
when I said "it just doesn't".

What IS the straight answer? The dropping something in a moving vehicle
analogy doesn't work, does it? A plane has a method of acceleration, whereas
a passively dropped object doesn't.

A dropped object is indeed accelerating (down).

It's just that the Coriolis effect isn't that significant. Note that rocket
launches are to the east (and why they try to launch them as close to the
equator as possible).

Maybe tonight I can pull out my old (VERY old) Physics references and
run some numbers...

--
Bob Noel
Looking for a sig the
lawyers will hate

Bob Noel wrote:
Note that rocket launches are to the east (and why they try to launch
them as close to the equator as possible).

I think equatorial launch sites are only advantageous for certain types of
desired orbits.

In any case, this is an area in which the Europeans have the Americans
beat. We launch from Florida, at about 30N, they launch from Kourou,
French Guiana, at about 5N.

"xerj" wrote in message
...
I was talking about Coriolis effect with someone and he asked me about
planes against or with the earth's spin of around 1000mph at the equator.
He asked why this didn't benefit east to west plane travel timewise and
hurt west to east. I couldn't give him a straight answer, and felt like an
idiot when I said "it just doesn't".

What IS the straight answer? The dropping something in a moving vehicle
analogy doesn't work, does it? A plane has a method of acceleration,
whereas a passively dropped object doesn't.

Sometimes really simple questions can give you the worst time.


Is the wind outside blowing at 1000 mph right now? The atmosphere, the
medium in which we fly, is spinning with the planet.

On Tue, 05 Dec 2006 08:38:56 -0500, Roy Smith wrote:

Bob Noel wrote:
Note that rocket launches are to the east (and why they try to launch
them as close to the equator as possible).

I think equatorial launch sites are only advantageous for certain types of
desired orbits.

In any case, this is an area in which the Europeans have the Americans
beat. We launch from Florida, at about 30N, they launch from Kourou,
French Guiana, at about 5N.

Boeing launches from the equator.

http://www.boeing.com/special/sea-launch/

The Earth's spin gives a "head start" of about 900 nautical miles per hour
towards the east. This tapers off as the launch site latitude increases, IIRC,
it's a function of the cosine of the latitude. So Cape Canaveral gets a ~800
nmph boost.

The amount of assistance this gives any particular launch depends on the
inclination of the orbit...the 'tilt' of the orbit plane relative to the
equatorial plane. The more inclination, the less benefit from the Earth's spin.

Geostationary orbits (those which allow a satellite to hang stationary relative
to the Earth's surface) are probably the most valuable; these have zero
inclination and thus benefit the most from a lower-latitude launch site.
Sun-Synchronous orbits, which are used by imaging satellites, have inclinations
over 90 degrees and thus see no benefit from equatorial launch. The US uses
launch sites in California and Alaska for these types of launches.

Airplanes fly relative to the atmosphere. Since the atmosphere moves with the
Earth's spin, aircraft see no advantage from eastward flight.

Ron Wanttaja

He asked why this didn't benefit
east to west plane travel timewise and hurt
west to east.

The short answer is that although one =is= moving faster going eastwards
(due to the addition of the spin of the earth), your destination is also
scurrying away from you at the same speed. It cancels out. There are
teeny effects (having to do with orbital mechanics) but those are not
the ones that are important in understsanding the question.

The flaw in your friend's reasoning (the reason for his question) has to
do with using different frames of reference for different parts of the
question - i.e. the earth is =not= spinning with respect to its surface
(the ground "stays put" with respect to itself!) but it =is= spinning
with respect to its center. We navigate with respect to the earth's
surface, not the earth's center. We fly with respect to the wind, which
moves over the earth's surface, which is what leads to the illusion of
flying sideways (crabbing into the wind). In this respect, one's
destination really =is= slipping away below you!

The "dropping something from a moving vehicle" does work quite well as
an analogy. Acceleration (from the airplane engine) has little to do
with it. The key is that although the frame of reference (the earth's
surface, or the vehicle) is moving, it is not moving with respect to
itself, since by definition, it =is= the frame of reference.

Now, this introduces some additional issues, which are the ones normally
referred to as the coriolis effect. Since the earth is roughly
spheerical and rotating, different parts of the earth are moving (w.r.t.
its center) at a different speed. The poles are hardly moving, and the
equator is moving fast (which is why, all things equal, you'd be lighter
at the equator). If you fire a cannon from the North Pole (in the only
direction possible - South), the cannonball will not be in contact with
the earth's surface, and as it travels towards the equator, the earth
will be spinning out from under it. Now while the muzzle of the cannon
may have been moving (one revolution per day, maybe fifty feet per day,
as the cannon is attached to the earth's surface), this is next to
nothing compared to the speed the equator is moving. The Sahara desert
and the Amazon River will both be scooting out from under this
cannonball at a thousand miles per hour. You, riding on the cannonball,
will get a good sense of the earth spinning under you. However, anybody
looking up at the cannonball from the ground will see the same thing in
reverse - the cannonball will be slipping the other way through the air
- east to west, just like the sun and moon rise. The closer to the
equator, the bigger the effect, and that is what gives rise to the large
scale air circulations in the earth.

Jose
--
"There are 3 secrets to the perfect landing. Unfortunately, nobody knows
what they are." - (mike).
for Email, make the obvious change in the address.

The earth spinning DOES affect long range aircraft flight. Going west
to east, you generally have tailwinds (in the northern hemisphere) and
lose an hour of daylight for every 800 miles or so. Going east to west
you have headwinds but you pick up an hour of daylight for every 800
miles or so. It actually sort of evens out.

The earth's rotation and the coriolis effect has signifigant difference
on the weather, the jet stream and the direction highs and lows
circulate.

If you shoot an artillery shell from north to south the coriolis effect
is signifigant enough so you have to account for it in your aiming
calculations. This is because the ground velocity of the earth due to
spinning is greater at the equator than it is to the north or south.
This doesnt make much difference with aircraft becaus they are flown
and not aimed rockets or artillery shells.

The bottom line is the coriolis effect has some subtle difference on
small GA flight, but not much.

It cancels out.
False. The question specifically asked about Coriolis force
- that force is tiny, but it's not zero.

The question named "coriolis force" but referred to effects other than
that. The effect alluded to would be there even on an infinite flat
earth which was moving (though not rotating). To this end, I addressed
that first, and to first order, ("short answer"), the motion of the
destination is cancelled out by the (additional) motion of the aircraft
due to the motion of the destination. The =actual= coriolis effect is a
second order effect due to the fact that the earth's motion is a
rotation, which I addressed later.

There are
teeny effects (having to do with orbital mechanics)

This has nothing to do with orbital mechanics, it's just
plain physics - albeit the physics of rotating reference
systems.

Orbital mechanis =is= "plain physics". The effect I was talking about
was the lightening of an object due to its motion around the earth;
taken to an orbital limit the object becomes weightless, but at slower
speeds reduces the amount of lift needed (and thus drag induced).

There was no flaw in the friend's reasoning. He was
absolutely right to ask about the Coriolis effect.

Of course he's right in asking about the coriolis effect, but that's not
the effect he seemed to be referring to.

he asked me about planes against
or with the earth's spin...

He asked why this didn't benefit east to west
plane travel timewise and hurt west to east.

What is commonly called the coriolis effect has to do with apparant
deflection of a flight path due to travelling to a place where the
velocity of the earth (due to rotation) is different. Generally this
means having a north/south component.

If the plane flew faster, the effect would be greater.

The effect you're apparantly referring to (centrifugal "force") would
increase with velocity. However, the effect commonly called the
coriolis effect is more pronounced at slow speeds, where the earth has
more of a chance to spin out from under you.

[presumably you are referring to:]
...The key is that although the frame of reference (the earth's
surface, or the vehicle) is moving, it is not moving with respect to
itself, since by definition, it =is= the frame of reference.

This is all either wrong or irrelevant to the question.

The question asked and the underlying misunderstanding are different. I
attempted to address them both. And what I said is =not= wrong. You
may be confusing "moving with" with "accelerating with respect to".

It's a good thing I'm not Mx.

Jose
--
"There are 3 secrets to the perfect landing. Unfortunately, nobody knows
what they are." - (mike).
for Email, make the obvious change in the address.

xerj wrote:
I was talking about Coriolis effect with someone and he asked me about
planes against or with the earth's spin of around 1000mph at the equator. He
asked why this didn't benefit east to west plane travel timewise and hurt
west to east. I couldn't give him a straight answer, and felt like an idiot
when I said "it just doesn't".

What IS the straight answer? The dropping something in a moving vehicle
analogy doesn't work, does it? A plane has a method of acceleration, whereas
a passively dropped object doesn't.

Sometimes really simple questions can give you the worst time.

It does affect us to some degree. We refer to it as "prevailing winds".
Remember that we are sitting in air above the earth that is moving
(mostly ) with the earth so the difference would not be as great as
your friend may imagine. The difference between the two rates comes
from the friction between the winds and the earth.

-Robert