HandbookHandbookSKILLSSKILLS

Measuring in SIThe standard system of measurement used byscientists around the world is known as theInternational System of Units, which is abbrevi-ated as SI (Système International d’Unités, inFrench). SI units are easy to use because they arebased on multiples of 10. Each unit is ten timeslarger than the next smallest unit and one tenththe size of the next largest unit. The table lists theprefixes used to name the most common SI units.

Length To measure length, or the distancebetween two points, the unit of measure is themeter (m). The distance from the floor to a door-knob is approximately one meter. Long distances,such as the distance be-tween two cities, aremeasured in kilometers(km). Small lengths aremeasured in centimeters(cm) or millimeters(mm). Scientists usemetric rulers and metersticks to measure length.

Liquid Volume To measure the volume of aliquid, or the amount of space it takes up, youwill use a unit of measure known as theliter (L). One liter is the approximate volume ofa medium-size carton of milk. Smaller volumesare measured in milliliters (mL). Scientists usegraduated cylinders to measure liquid volume.

Making Measurements

CommonConversions

1 km = 1,000 m

1 m = 100 cm

1 m = 1,000 mm

1 cm = 10 mm CommonConversion

1 L = 1,000 mL

By measuring, scientists can express their observations more preciselyand communicate more information about what they observe.

1

The larger lines on the metric ruler in thepicture show centimeter divisions, whilethe smaller, unnumbered lines show mil-limeter divisions. How many centimeterslong is the shell? How many millimeterslong is it?

The graduated cylinder inthe picture is marked inmilliliter divisions. Noticethat the water in thecylinder has a curved surface. This curved surface is called themeniscus. To measure the volume, you mustread the level at the lowest point of themeniscus. What is the volume of water in thisgraduated cylinder?

Common SI Prefixes

Prefix Symbol Meaning

kilo- k 1,000

hecto- h 100

deka- da 10

deci- d 0.1 (one tenth)

centi- c 0.01 (one hundredth)

milli- m 0.001 (one thousandth)

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Skills Handbook

Converting SI UnitsTo use the SI system, you must know how toconvert between units. Converting from oneunit to another involves the skill of calculating,or using mathematical operations. Convertingbetween SI units is similar to convertingbetween dollars and dimes because bothsystems are based on multiples of ten.

Suppose you want to convert a length of80 centimeters to meters. Follow these steps toconvert between units.

1. Begin by writing down the measurement you want to convert—in this example,80 centimeters.

2. Write a conversion factor that represents the relationship between the two units youare converting. In this example, the relation-ship is 1 meter = 100 centimeters. Write thisconversion factor as a fraction, making sure to place the units you are convertingfrom (centimeters, in this example) in the denominator.

3. Multiply the measurement you want to convert by the fraction. When you do this,the units in the first measurement will cancelout with the units in the denominator. Youranswer will be in the units you are convert-ing to (meters, in this example).

Example

80 centimeters � ■ meters

80 centimeters � �

� 0.8 meters

Safety Appendi

80 meters100

1 meter100 centimeters

Mass To measure mass, or the amount ofmatter in an object, you will use a unit ofmeasure known as the gram (g). One gram isapproximately the mass of a paper clip. Largermasses are measured in kilograms (kg). Scientists use a balance to find the mass of an object.

Temperature To measure the temperature of a substance,you will use the Celsius scale.Temperature is measured indegrees Celsius (°C) using aCelsius thermometer. Waterfreezes at 0°C and boils at 100°C.

Time The unit scientists use tomeasure time is the second (s).

CommonConversion

1 kg = 1,000 g

What is the temperature of the liquid in degreesCelsius?

The mass of the potato in the pictureis measured in kilograms. What isthe mass of the potato? Suppose a

recipe for potato salad calledfor one kilogram of potatoes.

About how many potatoeswould you need?

Convert between the following units.

1. 600 millimeters = ■ meters

2. 0.35 liters = ■ milliliters

3. 1,050 grams = ■ kilograms

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