How Much do We Weigh?

You have probably read about Sir Isaac Newton, and how he saw a falling apple and linked it up with the worlds in space through the law of gravity. This acts as though the earth were a great magnet which pulls things towards it. But we must think of the magnet as though it were not on the surface of the earth where we live, but buried deep at the centre, four thousand miles beneath our feet.

Since the earth is not quite a sphere, but bulges round the equator and is slightly flattened at the poles, we are farther from the magnet at the equator than we are at the poles, and so we weigh a little less on the equator.

If we get four thousand miles from the earth's surface a pound weight would weigh only four ounces. A man who weighs twelve stones would weigh only three stones at the same distance. On the moon, where the gravity pull is only one sixth of that of the earth, our twelve stone man would weigh no more than two stones.

As we have already seen, the space-traveller who is going up in a rocket will weigh three or four times more than normal, the exact increase depending on the speed of the rocket and how quickly it is accelerating. The men who have circled the earth in a space-craft have first experienced this great increase in weight and then the complete opposite. Once in orbit they become weightless, because the speed of their space-craft as it circles the earth tends to throw them outwards, and this just cancels out the pull of the earth's gravity.