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

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).
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