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

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.

"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

"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.

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

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.

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.

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

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.

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

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.