WHAT IS WEIGHT.

New Zealand Graphic, Volume IX, Issue 18, 30 April 1892, Page 461

WHAT IS WEIGHT.

A .schoolboy is often puzzled to account for the fact that people on the other side of the earth, with their feet pointing towards ours, do not fall off, and he never fully understands how this cannot happen until he realises that the earth pulls everything toward it whatever it may be.

In virtue ot the earth's pull a weight falls downward from a height with an ever-increasing speed, and a pendulum swings to and fro until its excursions have become so shortened by friction and the resistance of the atmosphere that it stops.

We usually speak of the force with which the earth pulls a thing toward it as the weight ot that thing, and when, in the common operation of weighing goods, we place them in one pan of a pair of scales and in the other place certain standards (which we speak of as hundredweights or pounds) until the earth’s pull on the goods is just balanced by the earth’s pull on the standard weights, then we may say that they have both the same weight, and we measure the weight of the goods by the standards we have employed. Supposing now we were to employ for weighing instead of the usual pair of scales a spring balance in which we measure the weight of a thing by the extent it. will stretch out a spring, and not by counterposing it with known standards, we should find a substance with such an instrument to be inconsistent with its weight ; it would weigh less at the top of a mountain than it would down at the bottom of a valley. It is very evident that the quantity of matter in the substance would remain unaltered during its transit from the top to the bottom of the mountain, although its weight increased.

The quantity of matter in a body is spoken of as its mass, a very short and convenient word.

It will now be perceived that change of position alone will not alter the mass of an article, although it may very materially alter its weight or the force with which it is pulled toward a planet. Here is a fanciful example to the point : There goes a jolly fellow who weighs sixteen stone if he weighs a pound ; in other words, the earth pulls at him with a force which would register sixteen stone if he were put into the pan of a very large spring balance.

Suppose him now, if it were possible, instantly transported to the surface, let ns say ot Jupiter. His mass would be unaltered, but upon sitting once more in the pan of the spring balance he would weigh only nine and three-tenths pounds.