You'd have to go a hell of a long way from Earth to be even close to truly "weightless," Jos, if by that you mean so far away that the effect of the Earth's gravity becomes, in effect, negligible (there's gravity everywhere,though). There's no sudden level in space where weightlessness "starts." though of course the effect can be achieved via certain manoeuvres of the space craft, being in orbit (free fall) being one of them, or momentarily when you reach the highest point your rocket takes you before you start to come down again. Indeed, the effect can be simulated at ground level. "Zero-g force" is a good way of putting it. You could go to the gravitational balance-point between the Earth and the moon, I suppose, but you'd have to sit very still. It's complicated and I am only a biologist.

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