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

[xerj]

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.

[Matt Whiting]

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

[Bob Noel]

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

[Roy Smith]

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.

[Gig 601XL Builder]

"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.

[Ron Wanttaja]

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

[Jose[_1_]]

> 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.

[Doug[_1_]]

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.

[Jose[_1_]]

>>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.

[Robert M. Gary]

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

[Mxsmanic]

xerj writes:

> 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.

The Coriolis effect is never a factor for east-west movement along the
Equator.

Additionally, the Coriolis effect due to the Earth's rotation is too
small to have a significant effect on an aircraft.

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

The Coriolis effect is not a factor for east-west movement along the
Equator.

Aircraft travelling in the direction of the Earth's rotation weigh
slightly less than aircraft travelling in the opposite direction
because of centrifugal acceleration, but that is unrelated to the
Coriolis effect and is too small to worry about in practice.

--
Transpose mxsmanic and gmail to reach me by e-mail.

[Danny Dot]

"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.
>

How about the fact the air the plane is flying through also is traveling
West to East. You are flying into a 1000 mph West to East headwind :-) A
100 mph airplane is flying backwards at 900 mph.

Danny Dot

[N2310D]

"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.

Hi xerj,
I think this is a great question. Back in the [Harumph!] old
days when I learned to fly we were taught in Metorlogy 101 that one indirect
way coriolis force DOES affect east or west airtravel is what it does to the
weather.

The following is quoted from:

TODAY'S TMJ4 WEATHER PLUS; Coriolis force affects wind patterns
Milwaukee Journal Sentinel, The, Sep 18, 2006 by MIKE LAPOINT

"When looking down at the North Pole, Earth spins counterclockwise around
its axis. A point on the equator travels about 1,100 mph, while the points
directly at the poles do not move at all. An apparent force called the
Coriolis force results from this difference in speeds, deflecting objects to
the right in the Northern Hemisphere and to the left in the Southern
Hemisphere. The Coriolis force, combined with solar heating patterns across
Earth, creates distinctive wind patterns that drive weather systems.
One prevailing surface wind pattern that results is in the mid- latitudes,
between 30 and 60 degrees north. Solar heating alone, without Earth's
rotation, would produce prevailing southerly winds. The Coriolis force,
however, deflects these winds to the right, creating prevailing winds out of
the west and southwest known as the westerlies."

So, while coriolis has only a small direct affect, the winds can be a huge
factor in slowing aircraft down on westerly flights. The above is just one
of a bunch of hits from Google about coriolis force and the weather.

[[email protected]]

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.

Coriolis effect has a very significant effect on planes, just not
directly. Its effect is felt in the wind patterns that is produces in
terms of high and low pressure centers and their rotation. Every time
you fly you account for the coriolis effect by checking the wind
forecasts and doing the wind correction calculations...

Dean

[Mxsmanic]

T o d d P a t t i s t writes:

> Coriolis force and Centrifugal force are both pseudo forces.

I didn't say anything about forces.

--
Transpose mxsmanic and gmail to reach me by e-mail.

[Jose[_1_]]

> C-force is a force, not a motion or change of motion.
> True, there will be some "deflection" if the force is not
> resisted, but often it is resisted, so there will be a
> force, but no deflection.

Exactly. When I said "deflection" I was referring to an unresisted
case. It is easier to visualize. Once visualized, it becomes evident
that resistance will generate a force, and that incomplete resistance
will still leave some deflection (which is what causes the winds to
circulate the way they do).

> C-force depends only on the
> velocity vector of the moving item...

but what I'll call Coriolis deflection (the result of unresisted
coriolis effect) depends on the time that has transpired. Consider the
cannon at the North pole again. When the Acme RapidFire SuperSonic
HighSpeed cannonball reaches the equator, it will be moving with next to
no angular velocity (around the polar axis) while the ground underneath
will be moving at a thousand miles an hour (eastward). Since the
cannonball got there in LicketySplit time, the earth will not have had
much time to move much, and the path would be pretty straight if drawn
on the globe. This is easy to visualize, which is why I used it as an
example. Now, resisted, there would have been a large force for a short
time, therefore a high acceleration. I believe this is what you are
referring to.

However, if we put a SlugBall (tm) into that cannon, and it took a good
six hours to get to the equator, and we also neglected air friction, the
SlugBall, taking the very same (with respect to the fixed stars) path,
would find that the earth has rotated a quarter of the way around in
that time. It would have hit the Amazon, now it hits the Sahara. When
drawn on the earth, the path is curved in a major way. This is also
easy to visualize. At slower speeds, the deflection is much greater.
Granted, if resisted, there'd be the same delta vee, over a much longer
time, and therefore a smaller force. But it's a bigger deflection on
the map unresisted.

This is why I was careful to say "coriolis effect" and not "coriolis
force". Perhaps that's a bit sloppy.

> Coriolis force is quite simply
> twice the vector cross product of the spin vector and the
> velocity vector.

Most people equate "cross product" with "teenager".

> If you are
> flying East at the equator and reach your orbital speed the
> Coriolis force will equal the force of gravity and be
> upwardly directed.

True, and in any case lessens the force on the wings, and thus the drag.
I hadn't put that much together as being the same coriolis force. It
could be said that coriolis force keeps a satellite in orbit. I think
doing so however would tend to muddy the water before clearing it up. :)

And the coriolis force on a southbound cannonball at the equator should
be zero. Yet that is where you'd see the greatest coriolis effect
("unresisted deflection"). You'd be going south by the fixed stars, and
the earth would be slipping past you right to left at a thousand miles
an hour.

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.

[Matt Whiting]

T o d d P a t t i s t wrote:

> Pilots tend to think of Coriolis force as being in one
> direction north of the equator, the opposite direction south
> of the equator and zero at the equator (if they think of it
> at all). However, it isn't zero at the equator, it's just
> pointed straight up.

Is it pointed straight up or only affects objects moving straight up?
My engineering mechanics and physics classes were more than two decades
ago so I'm a little rusty, but I believe that coriolis
acceleration/force doesn't act straight up at the equator, but acts
perpendicular to the motion of an object moving up or down as opposed to
along the earth's surface. For example, assume a rod extending upward
at the equator, but normal to the earth's surface. Now put a metal
doughnut on the rod and then lift it upward several hundred feet. The
doughhut will be accelerated by a force from the rod that acts in a
direction normal to the rod as the doughnut has to move faster as it
gains altitude, right?


Matt

[peter]

Matt Whiting wrote:
> T o d d P a t t i s t wrote:
>
> > Pilots tend to think of Coriolis force as being in one
> > direction north of the equator, the opposite direction south
> > of the equator and zero at the equator (if they think of it
> > at all). However, it isn't zero at the equator, it's just
> > pointed straight up.
>
> Is it pointed straight up or only affects objects moving straight up?

At the equator the Coriolis force would be straight up for an airplane
in level flight that's headed east and would be straight down if the
airplane is in level flight headed west. If the airplane is going up
or down then there would be a component of the Coriolis force towards
the west or east, respectively.

The direction of the Coriolis force will always be perpendicular to
both the velocity of the object (airplane in this case) and the axis of
the earth's rotation. In the case of level flight at the equator those
two vectors are in a plane that's tangent to the earth's surface at the
airplane's location and therefore the C. force is perpendicular and
must be directly up or down.

> My engineering mechanics and physics classes were more than two decades
> ago so I'm a little rusty, but I believe that coriolis
> acceleration/force doesn't act straight up at the equator, but acts
> perpendicular to the motion of an object moving up or down as opposed to
> along the earth's surface. For example, assume a rod extending upward
> at the equator, but normal to the earth's surface. Now put a metal
> doughnut on the rod and then lift it upward several hundred feet.

In that case the velocity vector is upward, the axis of earth's
rotation is toward the north, and therefore the force will be
perpendicular to both and toward the west. The rod must act to oppose
that force if the donut is to travel straight up, so it exerts a force
toward the east.

> doughhut will be accelerated by a force from the rod that acts in a
> direction normal to the rod as the doughnut has to move faster as it
> gains altitude, right?

Yes.

[Bob Noel]

In article >,
Roy Smith > 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.

true. But, not too many launch customers want polar orbits. And I don't
think there is any penalty for launching near the equator.

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

[Bucky]

Matt Whiting wrote:
> 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.

Right. I think Xerj was confused because he was talking Coriolis effect
and someone asked him why flying against the earth's spin isn't faster.
The simple answer to that question is Newton's first law of inertia.

The second question is how come it's faster to fly with the earth's
spin then? The answer to that is that winds generally blow from west to
east in the northern hemisphere... which is partially due to the
Coriolis effect (as well as heating patterns). But that's an indirect
effect.

[Roy Smith]

Jose > wrote:
> Orbital mechanis =is= "plain physics".

What makes orbital mechanics complicated is not that it isn't plain
physics, but that it isn't plane physics :-)

[Jose[_1_]]

> What makes orbital mechanics complicated is not that it isn't plain
> physics, but that it isn't plane physics :-)

It is if your plane moves fast enough. :)

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]

Thanks to all who answered!

"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.
>

[Bucky]

T o d d P a t t i s t wrote:
> However, the original question was
> about whether the Coriolis effect would "benefit east to
> west plane travel timewise and hurt west to east"

Actually, that wasn't the original question, which is what I was
alluding to when I said "Xerj was confused." Xerj's friend simply asked
how come flying against the earth's spin isn't faster than flying with
the earth's spin? This is straight up an inertia question.
Unfortunately, the question proceeded a discussion on Coriolis effect,
making it sound like it was related to Coriolis effect.

[The Visitor]

Jose wrote:

> taken to an orbital limit the object becomes weightless,

An object in orbit is not weightless. That's why it's held in orbit, by
gravity. If it was weightless, gravity could not act on it. It would not
have inertia. An object in orbit is actually in a constant state of
freefall. That's why you feel weightless, and things float about, when
in orbit.

Or when you make an airplane out of an orange crate and jump off the
garage roof. Nevermind....

John

[Jose[_1_]]

> If it was weightless, gravity could not act on it.

"If it were..." (not "if it was..."). Don't confuse weightless with
massless. Mass is the quantity that is conserved, and gives inertia.
Weight is the =force= due to gravity on that object. In a free falling
frame, an object is weighless, despite its mass.

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.

[Ron Wanttaja]

On Wed, 06 Dec 2006 19:51:46 -0800, Richard Riley >
wrote:

>On Tue, 05 Dec 2006 07:48:41 -0800, Ron Wanttaja
> wrote:
>
>>
>>Boeing launches from the equator.
>>
>>http://www.boeing.com/special/sea-launch/
>
>And Ariane launches from close to the equator
>http://www.arianespace.com/site/spaceport/spaceport_sub_index.html
>
>> The US uses
>>launch sites in California and Alaska for these types of launches.
>
>I didn't know we launch from Alaska. I mean, except for the GMD
>stuff. Huh.

They put an Athena into LEO from the Kodiak Launch Complex a few years back.

http://www.astronautix.com/sites/kodiak.htm

And, of course, are eager for more business.

http://www.akaerospace.com/facilities.html

They've hosted events like small satellite conferences; I visited a couple of
years back. VERY slick setup. It's amazing to visit a space launch center
where EVERYTHING is brand new. And where they've got free-range bison in the
launch control center parking lot....

http://www.wanttaja.com/ron&bison.jpg

Ah, well. Gators at Cape Canaveral, Californians in Vandenberg. :-)


Ron Wanttaja

[The Visitor]

Jose wrote:

> "If it were..." (not "if it was...")

You're kidding, right?

Don't confuse weightless with
Mass is the quantity that is conserved,
I wasn't. I didn't know masses changed. By saying "conserved" are you
saying some went away. Do you mean 'constant'?





> Weight is the =force= due to gravity on that object. In a free falling
> frame, an object is weighless, despite its mass.
>


If it doesn't weigh anything, why is it falling?

Does it expierience microgravity?

[Jose[_1_]]

>> "If it were..." (not "if it was...")
>
> You're kidding, right?

Nope. "Were" is used with a subjunctive ("contrary to fact") condition.
"The sky isn't blue, but if it were, I could fly today."

> I didn't know masses changed.

Except for nuclear reactions and high speeds, they don't. "Conserved"
(in physics) refers to a quantity the same before and after. For
example, a point can change how far north it is from another point
simply by changing the reference frame (magnetic, true), but the
distance is conserved.

In the statement I made about mass, "constant" works just as well, but
"conserved" is more to the point, as we are changing reference frame.

> If it doesn't weigh anything, why is it falling?

It isn't. It's remaining right where it is. Only in the earth's
reference frame is it falling (accelerating downwards). But the earth's
frame is not the free-falling one I was talking about. In the reference
frame of the falling object, nothing at all is happening to it. It's
staying right where it is. ("Where are you?" "I'm right here. I'm
always 'right here', why do you keep asking!")

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.

[Stealth Pilot]

On 5 Dec 2006 10:49:02 -0600, T o d d P a t t i s t
> wrote:

>Ron Wanttaja > wrote:
>
>>Airplanes fly relative to the atmosphere. Since the atmosphere moves with the
>>Earth's spin, aircraft see no advantage from eastward flight.
>
>Airplanes fly relative to whatever frame of reference you
>want to use. If you use the spinning earth as a frame of
>reference, then any motion in that frame produces
>centrifugal or Coriolis force. Those forces affect the
>amount of lift the plane must produce (unless they are
>entirely horizontal.) The amount of lift affects the amount
>of drag, and that affects fuel consumption. For relatively
>low speeds, the effect on fuel consumption is tiny, but it
>is measurable.

two comments on your posts

centrifugal force does not exist. it is an engineering misconception.
the force involved is inertia.

aeroplanes fly relative to the atmosphere they fly in.
mathematical abstractions are based on frames of reference.
the two are not the same.
wantajja's post was correct.
Stealth Pilot

[darthpup]

For those who would like an answer get a reference to geostrophic ocean
flow. You will need to solve three partial differential calculus
equations, by Euler, to understand this question.
Any basic text on physical oceanography or meterology will do this for
you.