Weight and Mass
Weight is the measure of how heavy an object is. Weight is measured in standard customary units.
The mass of an object is the amount of material it contains. Mass is measured in standard metric units.
For everyday purposes, when you're on the surface of the earth, the difference is not important. But if you measure something on another planet, its mass will be the same as it is on earth—but its weight will be different. (Weight depends on gravity, and gravity is different on other planets! This is why when you're floating in space, you'reweightless.You still have mass, though,)
Metric Units
Thegramandkilogramare two units used to measure mass in themetric system.
From the gram, we get the rest of the metric units using the standard metric prefixes.
Milligram(mg) |
gram orgram |
Centigram(cg) |
gram orgram |
Decigram (dg) |
gram orgram |
Gram(g) |
milligrams |
Dekagram (dag) |
grams |
Hectogram (hg) |
grams |
Kilogram (kg) |
grams |
Metric ton(t) |
kilograms |
A paper clip has a mass of aboutgram.
Aliter bottle of water has a mass ofkilogram (plus a little bit extra for the plastic).
U.S. Customary Units
The system for measuring weight (not mass) in the customary system is based on ounce, pound, and ton. The basic unit of weight is a pound(lb).
An ounce is the smallest unit of weight. A strawberry has a weight of aboutounce.
A car has a weight of abouttons.
To convertfrom one unit to another, we can useunit analysis. For example, a truck weightspounds. How many tons is this?
We know that.
To convert pounds to tons, you can divideby.
.
Note:
(a) To convert from larger units to smaller units, multiply by the appropriate unit ratio.
(b) To convert from smaller units to larger units, multiply by thereciprocalof the appropriate unit ratio.
(c) Multiplying or dividing by a unit ratio is mathematically equivalent to using aproportiontoconvert between units of measure.