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The SI (Metric) System

Instruments that use the Metric

System

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The Standard Units• Scientists generally report results

in an agreed upon International System.

• The SI SystemAka Système International

Quantity Measured Name of Unit Abbreviation

Mass kilogram kgLength meter mVolume liter LTime seconds sTemperature Kelvin K

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International Usage of the

SI System

Freeway Sign in China

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Length• Measure of the two-dimensional distance an object

covers.• SI unit = meter

About 3½ inches longer than a yard.• 1 meter = one ten-millionth the distance from the

North Pole to the Equator = distance between marks on standard metal rod in a Paris vault = distance covered by a certain number of wavelengths of a special color of light

• Commonly use centimeters (cm). 1 cm ~ width of your pinky nail 1 m = 100 cm 1 cm = 0.01 m = 10 mm 1 inch = 2.54 cm (exactly)

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Mass• Measure of the amount of

matter present in an object.• SI unit = kilogram (kg)

About 2 lbs. 3 oz.• Commonly measure mass in

grams (g) or milligrams (mg).1 kg = 2.2046 pounds, 1 lbs. =

453.59 g1 kg = 1000 g = 103 g, 1 g = 1000 mg = 103 mg1 g = 0.001 kg = 10-3 kg, 1 mg = 0.001 g = 10-3 g

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Estimate the Mass of a Quarter in Grams

• 2.5 g• 5.5 g• 8.5 g• 10 g• 15 g

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Estimate the Mass of a Quarter in Grams,

Continued • 2.5 g• 5.5 g• 8.5 g• 10 g• 15 g

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Time• Measure of the

duration of an event.

• SI units = second (s)

• 1 s is defined as the period of time it takes for a specific number of radiation events of a specific transition from cesium-133.

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Temperature• Measure of the average

amount of kinetic energy (molecular motion).higher temperature = larger

average kinetic energySI unit = Kelvin (K)

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Related Units in the SI System

• All units in the SI system are related to the standard unit by a power of 10.

• The power of 10 is indicated by a prefix.

• The prefixes are always the same, regardless of the standard unit.

• It is usually best to measure a property in a unit close to the size of the property. It reduces the number

of confusing zeros.

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Common Prefixes in the SI System

Prefix SymbolDecimal

EquivalentPower of 10

mega- M 1,000,000 Base x 106

kilo- k 1,000 Base x 103

deci- d 0.1 Base x 10-1

centi- c 0.01 Base x 10-2

milli- m 0.001 Base x 10-3

micro- m or mc 0.000 001 Base x 10-6

nano- n 0.000 000 001 Base x 10-9

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Prefixes Used to Modify Standard Unit

• kilo = 1000 times base unit = 103

1 km = 1000 m = 103 m• deci = 0.1 times the base unit = 10-1

1 dL = 0.1 L = 10-1 L; 1 L = 10 dL• centi = 0.01 times the base unit = 10-2

1 cm = 0.01 m = 10-2 m; 1 m = 100 cm• milli = 0.001 times the base unit = 10-3

1 mg = 0.001 g = 10-3 g; 1 g = 1000 mg• micro = 10-6 times the base unit

1 m = 10-6 m; 106 m = 1 m• nano = 10-9 times the base unit

1 nL = 10-9L; 109 nL = 1 L

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Practice—Which of the Following Units Would Be Best Used for Measuring the

Diameter of a Quarter?

a) kilometer

b) meter

c) centimeter

d) micrometer

e) megameters

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Practice—Which of the Following Units Would Be Best Used for Measuring the

Diameter of a Quarter?, Continued

a) kilometer

b) meter

c) centimeter

d) micrometer

e) megameters

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Volume• Derived unit.

Any length unit cubed.• Measure of the amount of

space occupied.• SI unit = cubic meter

(m3)• Commonly measure liquid

or gas volume in milliliters (mL).1 L is slightly larger than 1

quart.1 L = 1 dm3 = 1000 mL =

103 mL 1 mL = 0.001 L = 10-3 L1 mL = 1 cm3

SI Prefix Conversions

20 cm = ______________ m

0.032 L = ______________ mL

45 m = ______________ nm

805 dm = ______________ km

0.2

0.0805

45,000

32

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Common Units and Their Equivalents

Length1 kilometer (km) = 0.6214 mile (mi)

1 meter (m) = 39.37 inches (in.)1 meter (m) = 1.094 yards (yd)

1 foot (ft) = 30.48 centimeters (cm)1 inch (in.) = 2.54 centimeters (cm)

exactly

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Common Units and Their Equivalents, Continued

Volume

1 liter (L) = 1000 milliliters (mL)

1 liter (L) = 1000 cubic centimeters (cm3)

1 liter (L) = 1.057 quarts (qt)

1 U.S. gallon (gal) = 3.785 liters (L)

Mass

1 kilogram (km) = 2.205 pounds (lb)

1 pound (lb) = 453.59 grams (g)

1 ounce (oz) = 28.35 (g)

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Which Is Larger?

• 1 yard or 1 meter?

• 1 mile or 1 km?• 1 cm or 1 inch?• 1 kg or 1 lb?• 1 mg or 1 mg?• 1 qt or 1 L?• 1 L or 1 gal?• 1 gal or 1000

cm3?

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Which Is Larger?, Continued

• 1 yard or 1 meter?

• 1 mile of 1 km?• 1 cm or 1 inch?• 1 kg or 1 lb?• 1 mg or 1 ng?• 1 qt or 1 L?• 1 L or 1 gal?• 1 gal or 1000

cm3?