Something I've meant to ask each time this discussion comes up: If the car if going due west at 65 and the fly is going the opposite at 5, then from the observer's viewpoint, is the fly going 60 mph?
The same with the earth. If the earth's rotational direction is east, and the fly and car are both going west, is the speed from the observer's position 1100-70mph, 1030 mph.
And is a runner's speed faster or jump longer if running/jumping from the west to the east?
The flight path of the fly is moot in the example - i.e. whether he is flying in a straight line in the car, circling your head or zig-zagging. In the example, it's simply the distance being covered over a certain amount of time and to the observer watching him from a roadside table, the total distance and total time, i.e. cumulative.
Likewise, since the fly-watching observer in the example is under the same gravitational pull of the earth, the distance shortened by the West-East rotation of the earth is moot. The observer is being taken on the earth's surface in the same direction and speed as the fly and the car.
At higher elevations, even while orbiting within the gravitational well of the earth, the differences would be more measurable. Likewise, the reduction of distance traveled by a man jumping West (or added by jumping East) would be moot though the affect would be measurable at higher elevations, i.e. away from the gravitational well.
This has been tested also concerning time. The lower the gravity, the faster time elapses. Conversely, the higher the gravity, the slower time elapses. So if you were in the vicinity of a black hole for a week, for instance, 40 years may have elapsed on earth.
Interestingly flights going East-West take longer than flights going West-East not in contradiction of these factors but because of the West-East direction of the jet streams (tail winds.)
The example I used presumes that, except for the fly-watching observer, mph observations are absolute, i.e. not relative to an observer "in" space/time.
For instance, if the observer were "in" the space/time fabric between the Milky Way galaxy and Andromeda - the 486,000 miles our solar system travels in an hour would be so small by comparison to the size of the Milky Way, that the whole Milky Way galaxy might appear to him as if it were moving in "slow motion."
Inhabitants of space/time all suffer from the "observer problem."
Only God the Creator can objectively perceive His creation. He and He alone sees "all that there is" all at once. Every where. Every when. And He alone knows the full number and types of dimensions (space, time, etc.)
That He cares to observe thrills me. For without that will, there would be no justice, no objective Truth - it would all be observer relative.
And that He numbers every hair on our heads - despite what we mortals can perceive about of the cosmos or the quantum - comforts me.
God's Name is I AM.
(Then, you might ask the guys at Vandenberg...) '-)
Since the jumper's run and flight are relative to fixed points on the rotating surface of the earth, the differences cancel out. Neither direction gives a jumping advantage.
An observer at a remote point that is stationary with respect to a line through the earth's center would see the EASTWARD-running jumper's running speed as INCREASED by the rotation of the earth. BUT -- while he is in flight, his landing point rotates AWAY FROM him by a compensating distance... (He is "chasing a moving target...")
The opposite is true for a westward-running jumper. With no wind, equal effort produces equal jumps.
Once contact is broken, (most of) angular velocity is converted into linear velocity. That's what killed Goliath... '-)