Why don't we see ourselves flying around the Earth?

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David Ngwenya

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David Ngwenya asked the Naked Scientists:
The planets, the moon (and other satellites) and the sun are spherical bodies suspended in space.

When flying east, west, south or north over our planet earth (any horizontal direction) in an aeroplane, we eventually come back to where we started. What perturbs me is that we do not at any point see ourselves flying on the side or under the spherical earth.

(a) Why is this so.

(b)The horizontal flight would more or less keep the same distance from the earth and, not strictly tangentially when we would expect to leave the earth.

(c) The flight is in a straight line that can be confirmed even by a spirit level, but when viewed in its entirety, it will be circular. Will a tangential flight also be a very much wider circle.

(d) If our flight is in a spacecraft to the moon, it leaves earth going above, but we have seen the moon landing as touching down from above. (similarly when flying from the moon or outer space to the earth).

(e)Straight lines should be straight and not circular, this baffles me.

What do you think?


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Why don't we see ourselves flying around the Earth?
« Reply #1 on: 19/01/2009 15:21:18 »
It all bcomes much easier when you realise that the most stable shape for a self gravitiatin lump of matter is approximately spherical.  The oblateness depends on the rate at which it rotates therefore large objects with large gravitiational fields do not depart much from spherical.  The gravitational field of a sphere is as if all its mass was concentrated at its centre ai the attractive forece is always perpendicular to the surface of the sphere.
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