Page:A Voyage in Space (1913).djvu/191

Rh hanging weight G drops to its lowest point, pulling the slider A towards the centre E. But now let us spin the apparatus about the vertical axis FK. The slider will tend to fly away from the axis and will pull up the weight G, unless we make G very heavy. If G is heavy enough it will hold A near the centre; but if it is not heavy enough A will fly out.

Whether G is heavy enough depends on how fast we spin the apparatus. If we spin it slowly, G will be strong enough to hold A in close; but as we spin faster and faster, A tries harder and harder to fly out from the centre and is at last too much for G. This is very much what happens in the formation of a satellite. If the parent body is spinning slowly, its gravity or attraction (which we have represented by the weight G and the string) will hold