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Since the earth is rotating, why can't a plane that is flying from say, Perth to Johannesburg, just hover in the air and wait for Jo'burg to arrive underneath?

CuriousPerson
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    When you jump in the air, does the earth rotate under your feet? Can you put your car in neutral and "let the earth move your car"? Air moves with the earth too... – Ron Beyer Feb 28 '16 at 19:02
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    Well, in a certain sense it does. But it has to run its engines, or it would be blown eastward by the air that's rotating along with the Earth :-) – jamesqf Feb 28 '16 at 19:42
  • @jamesqf No it doesn't. What happens when you launch a lighter than air balloon in no wind? An aircrat needs engines to produce enough speed to gain lift since it's heavier than air. – Simon Feb 28 '16 at 19:44
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    @Simon: The balloon is carried eastward by the rotating air, of course. Lift is a separate issue: suppose you had a dirigible: with no power, it's carried with the wind; with sufficient power (and ignoring structural issues) it remains stationary in a celestial reference frame while the Earth rotates under it :-) – jamesqf Feb 28 '16 at 19:50
  • @jamesqf It's not "carried" or blown anywhere. There is no force acting on the balloon with no wind other than upwards as a consequence of it rising. When the balloon is on the ground, it is doing 1000mph. When you release it, it is still doing 1000mph. Only if there is any wind or some other force will that change. The Earth, the balloon and the atmosphere are all moving at 1000mph. A balloon in zero wind, will not move laterally. Newtons 1st. – Simon Feb 28 '16 at 20:02
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    @Simon: Now that depends. In a frame of reference fixed to the stars, the balloon, like the air and ground, is moving at about 1000 mph (if you're at the equator). If you run engines to cancel that movement WRT the fixed stars, you will move WRT the air and ground. It's all in how you look at it :-) – jamesqf Feb 29 '16 at 04:29
  • @jamesqf Please take it to Physics.SE. There is no such thing as "fixed stars", all of space is moving.The Earth is not an inertial reference frame and the fact remains that if you release a balloon, and there is no wind, it is not carried anywhere. It continues to move as it did before until acted upon by an external force, i.e. it moves at the same speed is the Earth surface and the atmosphere (ignoring some minor side effects). If it's mass was such that it hovered at 10 metres and it was a closed system, it would stay there until something caused it to move. There is no lateral force. – Simon Feb 29 '16 at 06:57
  • @jamesqf The relative speeds between the Earth, the atmosphere and the balloon are independent of any observer. Only their magnitude varies. Conduct a quick thought experiment. Release the balloon inside a room. Does it get carried into the wall? Why not? The atmosphere exerts no force on the walls of the room apart from the uniform force of pressure. – Simon Feb 29 '16 at 06:58
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    @Simon you are, of course, right in this matter, though I have to give jamesqf credit for taking the OPs point of view. I think he is perfectly aware of the fact that the balloon is not going anywhere when you release it up in the air. He said "in a certain sense [the plane] does [hover]" and I agree. Say you're on the sun, and see an airplane flying west with the same airspeed the earth rotates with, wouldn't it "stand still" ? So yeah, you are definitely right, but I don't think jamesqf is that wrong when giving the OP something to think about. – Maverick283 Feb 29 '16 at 11:34

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