h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

To my knowledge, gravity is attractive only. There are theories claiming that there might be an opposite of gravity but little evidence to support them. Gravity is a weak force but as it has no opposites, it can act over large distances and have a cumulative effect.

So though it may be overcome, gravity cannot be reversed.

Would the revolving of the Earth not cause a certain centrifugal force acting in opposition to the Earth's gravitational pull?

If so, supposing there was a way to accelerate the revolution, gravity could presumably be cancelled out when centrifugal force reaches a certain level.

Gravity cannot be reversed, but gravitational fields can, which is not the same thing. There Is evidence that the North and South poles where reversed at some time in the past and it is expected that it might happen again at some time in the future. But even so, gravity will still act towards the Earth's centre.

There is no such thing as centrifugal force. The effect that is mistakenly called centrifugal force is caused by gravity and Newton's first law of motion acting together.

Newton's first Law say that one a body is set in motion, it will continue in a straight line at a constant speed unless an acted on by another force. So a space ship set in motion will continue in a straight line, heading of into space, except that gravity tries to pull it back to earth. It produces a curved path that matches the curvature of the Earth. Speed and height is critical in making sure this happens.

If the speed of the Earth's rotation were to increase to such an extent that gravity was insufficient to keep unfixed objects like us from trying to continue in a straight line, then yes we would be thrown into space. As it is, gravity makes sure we follow a curved path that matches the Earth.

Likewise, if gravity was suddenly to be switched of, we would be thrown into space. It is not centrifugal force that is doing it, it is Newton's First Law of motion.

Donald

Well technically, it isn't Newton's first law that's doing it either, since that is just the formulation in words of the effect that the force has. What's doing it is the force exerted on us by the earth moving, which is what I in my ignorant shorthand called centrifugal force. But now we're splitting hairs