What instrument is used to find mass?

A scale

We don't measure mass directly; there is no "massometer." But we do have scales, which measure weight, which is directly proportional to mass. (Hyper-technically speaking, mass is a property of matter equal to its resistance to a change in speed or direction of travel.) The mass of an object is the same everywhere in the universe. Its weight, however, changes depending upon its location: a bowling ball has greater weight on the surface of the Earth than it does on the moon.

Great confusion arises when people interchange units of weight with units of mass. Scientists, particularly physicists, are very careful about not using the terms interchangeably, but regular folks have no choice if they want to get along in the world with other people. For example, when you weigh a regulation bowling ball used by the pros, the scale will tell you it "weighs" 7.27 kilograms, even though the kilogram is, technically speaking, a unit of mass, not weight.

More discussion on the units of weight and mass

[To be continued.]

Clarification to "A scale" above

Let's say you stand on a common bathroom scale near the surface of the Earth and the scale reads 100 pounds. If you then move to the surface of the Moon, however, the scale would read only 16.7 pounds. Bathroom scales are really spring devices and measure weight. The amount they display is dependent upon the force of gravity.

But what if you used a balance scale? You would stand on one tray of the balance scale, and weights are placed on the other tray until the scale balances. There would be 100 pounds of weights on the other tray. If you then move to the surface of the moon, you would NOT need to alter the weights on the other tray. No matter where the balance scale rests, it will always reveal the same result, in this case, 100 pounds. The balance scale doesn't measure weight; it measures mass!

Mass spectrometers

The closest thing to a "massometer" would be a mass spectrometer. It is used primarily to identify chemical compounds in an unknown substance and to determine isotopic element ratios in compounds. The exact amount of a substance in a compound can also be determined using mass spectrometry, but that is an involved process because mass spectrometry is not usually used to quantify exact amounts.

First answer by Millican. Last edit by Schnazola. Contributor trust: 1392 [recommend contributor]. Question popularity: 62 [recommend question]