# international system of units

## unit conversions

In the Table 1.2, two basic SI units are compared with their English system equivalents. You can use the information in the table to convert SI units to English units or vice versa. For example, from the table you know that 1 meter equals 39.37 inches. How many inches are there in 3 meters? 3 m = 3(39.37 in) = 118.11 in Measure Length Mass SI Unit meter (m) kilogram (kg) English Unit Equivalent 1 m = 39.37 in 1 kg = 2.20 lb Q: Rod needs to buy a meter of wire for a science experiment, but the wire is sold only by the yard. If he buys a yard of wire, will he have enough? (Hint: There are 36 inches in a yard.) A: Rod needs 39.37 inches (a meter) of wire, but a yard is only 36 inches, so if he buys a yard of wire he wont have enough.

## si units

The example of the Mars Climate Orbiter shows the importance of using a standard system of measurement in science and technology. The measurement system used by most scientists and engineers is the International System of Units, or SI. There are a total of seven basic SI units, including units for length (meter) and mass (kilogram). SI units are easy to use because they are based on the number 10. Basic units are multiplied or divided by powers of ten to arrive at bigger or smaller units. Prefixes are added to the names of the units to indicate the powers of ten, as shown in the Table 1.1. Prefix kilo- (k) Multiply Basic Unit 1000 Basic Unit of Length = Meter (m) kilometer (km) = 1000 m Prefix deci- (d) centi- (c) milli- (m) micro- () nano- (n) Multiply Basic Unit 0.1 0.01 0.001 0.000001 0.000000001 Basic Unit of Length = Meter (m) decimeter (dm) = 0.1 m centimeter (cm) = 0.01 m millimeter (mm) = 0.001 m micrometer (m) = 0.000001 m nanometer (nm) = 0.000000001 m Q: What is the name of the unit that is one-hundredth (0.01) of a meter? A: The name of this unit is the centimeter. Q: What fraction of a meter is a decimeter? A: A decimeter is one-tenth (0.1) of a meter.

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

what is the basic unit of mass in the international system of units?

``````a) ounce

b) pound

-->  c) gram

d) kilogram
``````

the prefix that multiplies a basic si unit by 0.01 is

``````a) kilo-

b) deci-

-->  c) centi-

d) milli-
``````

a kilogram equals one-thousandth of a gram.

``````a. true

-->  b. false
``````

## diagram questions

No diagram questions associated with this lesson