Properties of Matter

Mass and weight

Teaching Guidance for 14-16 PRACTICAL PHYISCS

The verb to weigh and the noun weight are used in conflicting ways, even in science.

You cannot hope to clear up the great distinction between mass and weight by narrowing down the use of those common words. Nor can you exclude them or replace them in science. Students have to learn to live with their sloppy complexity.

Therefore, at an introductory stage you might use weigh it to mean put it on the balance and see what the balance says. Others will want to drop the verb to weigh and ask students to find the mass of the object.

Even that is not very helpful, because what the balance feels, and what I feel if I put the object in my hand, is a force that arises from the pull of gravity on the object. This force is the object's weight. With a balance we are comparing the weight of one object with the weight of some other standard thing, a standard kilogram. That comparison will give the same ratio if we can transport the whole experiment to the Moon, or anywhere else where the gravitational field is strong enough to make the machine work at all.

Whatever you decide to do about the distinction between mass and weight, it is important to use these terms consistently. The student should insensibly acquire the right idea by the teacher's care in their use. Actually, the distinction between mass and weight comes fairly easily to some students in this space age, so be prepared to make a short, general comment if a good occasion arises.

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