2 - 1

MeasurementMeasurement

The Metric System and SI UnitsThe Metric System and SI UnitsConverting UnitsConverting Units

Measuring Volume and MassMeasuring Volume and MassDensityDensity

Measuring TemperatureMeasuring Temperature

2 - 2

SI UnitsSI Units

Many different systems for measuring the world around us have developed over the years.

People in the U.S. rely on the English System.

Scientists make use of SI units so that we all are speaking the same measurement language.

2 - 3

Data, results and unitsData, results and unitsDataData

Measurements and observations.ResultsResults

Data obtained from an experiment.May be converted using known equations.

UnitsUnitsDefines the quantities being measured.All measurements must have units.

To communicate our results, we must use standard units

2 - 4

Units are importantUnits are important

45 000 has little meaning, just a number

$45,000 has some meaning - money

$45,000/yr more meaning - person’s salary

2 - 5

Measurements Measurements English units. English units.

- Still commonly used in the United States.Weight ounce, pound, tonLength inch, foot, yard, mileVolume cup, pint, quart, gallon

Not often used in scientific workNot often used in scientific work - Very confusing and difficult to keep

track of the conversions needed.

2 - 6

MeasurementMeasurementEnglish units.English units. Vary in size so you must

memorize many conversion factors.

Common English measures of volumeCommon English measures of volume1 tablespoon = 3 teaspoons1 cup = 16 tablespoons1 pint = 2 cups1 quart = 2 pints1 gallon = 4 quarts1 peck = 2 gallons1 bushel = 4 pecks

2 - 7

ExampleExample

How many teaspoons in a barrel of oil?1 barrel of oil = 42 gallons1 gallon = 4 quarts1 quart = 4 cups1 cup = 16 tablespoons1 tablespoon = 3 teaspoons

1 bbl x 42 x 4 x 4 x 16 x 3galbbl

qtgal

cupqt

tblcup

tsptbl

= 32 256 tsp

2 - 8

Metric UnitsMetric Units One base unit for each type of measurement. Use a prefix to change the size of unit.

Some common base units.TypeType NameName SymbolSymbolMass gram gLength meter mVolume liter L Time second sEnergy joule J

MeasurementMeasurement

2 - 9

Metric prefixesMetric prefixes

Changing the prefix alters the size of a unit.PrefixPrefix Symbol Symbol Factor Factor

mega M 106 1 000 000

kilo k 103 1 000

hecto h 102 100

deka da 101 10

base - 100 1

deci d 10-1 0.1

centi c 10-2 0.01

milli m 10-3 0.001

2 - 10

SI unitsSI unitsSI - System InternationalSystem International

Systematic subset of the metric system.Only uses certain metric units.

Mass kilogramsLength metersTime secondsTemperature kelvinAmount moleCurrent ampere

Other SI units are derived from SI base units.

2 - 11

Example. Metric conversionExample. Metric conversion

How many milligrams are in a kilogram?

1 kg = 1000 g1 g = 1000 mg

1 kg x 1000 x 1000

= 1 000 000 mg

kgg mg

g

2 - 12

Converting unitsConverting units

Factor label methodFactor label method

•Regardless of conversion, keeping track of units makes thing come out right

•Must use conversion factors- The relationship between two units

•Canceling out units is a way of checking that your calculation is set up right!

2 - 13

Common conversion factorsCommon conversion factorsEnglish FactorFactor

1 gallon = 4 quarts 4 qt/gal1 mile= 5280 feet 5280 ft/mile1 ton = 2000 pounds2000 lb/ton

Common English to Metric conversions FactorFactor

1 liter = 1.057 quarts 1.057 qt/L1 kilogram = 2.2 pounds 2.2 lb/kg1 meter = 1.094 yards 1.094 yd/m1 inch = 2.54 cm 2.54 cm/inch

2 - 14

ExampleExampleCreatinine is a substance found in blood. If

an analysis of blood serum sample detected 0.58 mg of creatinine, how many micrograms were present?

= 10-6 = micro

0.580 mg = 580 g10-3 g1 mg( ) 1 g

10-6 g( )

2 - 15

ExampleExampleA nerve impulse in the body can travel as

fast as 400 feet/second.

What is its speed in meters/min ?

Conversions Needed

1 meter = 3.3 feet1 minute = 60 seconds

2 - 16

m 400 ft 1 m 60 secmin 1 sec 3.3 ft 1 min

ExampleExample

m 400 ft 1 m 60 secmin 1 sec 3.3 ft 1 min? = x x

? = x x

mmin ....Fast7273

2 - 17

Measuring volumeMeasuring volume

VolumeVolume - the amount of space that an object occupies.

• The base metric unit is the liter (L)liter (L).• The common unit used in the lab is the

milliliter (mL)milliliter (mL).• One milliliter is exactly equal to one cmcm33.• The derived SISI unit for volume is the mm33

which is too large for convenient use.

2 - 18

Measuring massMeasuring mass

MassMass - the quantity of matter in an object.WeightWeight - the effect of gravity on an object.

Since the Earth’s gravity is relatively constant, we can interconvert between weight and mass.

The SI unit of mass is the kilogram (kg)kilogram (kg). However, in the lab, the gram (g)gram (g) is more commonly used.

2 - 19

DensityDensityDensity is property of a substance based on

its ratio of mass to volume.

Common units are g / cm3 or g / mL.

g / cm3 g / cm3

Air 0.0013 Bone 1.7 - 2.0Water 1.0 Urine 1.01 - 1.03Gold 19.3 Gasoline 0.66 - 0.69

Density = Mass

Volumecm3 = mL

2 - 20

Example.Example.Density calculationDensity calculation

What is the density of 5.00 mL of a fluid if ithas a mass of 5.23 grams?

d = mass / volume d = 5.23 g / 5.00 mLd = 1.05 g / mL

What would be the mass of 1.00 liters of thissample?

2 - 21

Example.Example.Density calculationDensity calculation

What would be the mass of 1.00 liters of the fluid sample?

The density was 1.05 g/mL.density = mass / volume

so mass = volume x densitymass = 1.00 L x 1000 x 1.05

= 1.05 x 103 g

mlL

gmL

2 - 22

Temperature conversionTemperature conversion

Temperature - measure of heat energy.

Three common scales usedFahrenheit, Celsius and Kelvin.

oF = 32oF + (oC) X

oC = (oF - 32oF)

K = (oC + 273) X SI unit

5oC9oF

9oF5oC

1 K1oC

2 - 23

Example. Example. ooF to F to ooC C

If it is 20 oF outside, what is it in oC ?

oC = (oF - 32oF) 5oC9oF

oC = (20oF - 32oF) 5oC9oF

oC = -6.7 (two significant figures in 20oF)