Solution to

Frame 4-3.

System of measurement, the inch, foot, or yard is used to measure

length, the pound is used to measure weight, and the gallon is used to

SI (or metric)

measure volume. In the SI or metric system, you would use meters for

length, grams for mass, and liters for volume.

When using the metric system:

Length is expressed in

.

Mass is expressed in

.

Liquid capacity is expressed in

.

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Solution to

NOTE: In the remainder of this lesson, the term "metric" will be used to

Frame 4-4.

denote the SI system of measures.

meters

Notice that when the U.S. system was discussed in Frame 4-4, the term

grams

"weight" was used; but when the metric system was discussed, the term

liters

"mass" was used. "Weight" measures gravity's attraction to a given

object (its "heaviness"). Mass is a measure of an object's resistance to

acceleration (its inertia). In other words, mass is a measure of how

much matter is in the object while weight measures the force exerted by

the object. For our purposes, we can say that weight and mass are the

same. An object with a mass of 40 kilograms (40,000 grams), for

example, will weight the same anywhere on the surface of the earth

since the earth's gravity exerts the same pull. This works as long as you

are dealing with the earth's gravity, but what happens if you are not? An

object with a mass of 40 kilograms weighs about 88 pounds on earth.

On the moon, the same object would weight about 15 pounds since the

moon's gravitational pull is only one-sixth that of the earth's gravity. The

object's mass, however, would remain unchanged (40 kilograms), but it

would feel as heavy as a 6.7 kilogram weight on earth. In orbit around

the earth, the object would be weightless (zero pounds), but still retain

its mass (inertia) of 40 kilograms.

NOTE: In the U.S. system, the unit used to measure **mass **is the **slug**

(about 14,594 grams).

In scientific matters, it is usually easier to speak of an object's

rather than its weight since its

does not change. (Einstein's

theories of relativity are not considered in this subcourse.)

NOTE: For the remainder of this lesson, there will be no distinction

between "weight" and "mass."

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MD0900

4-3

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