Why Do We Need a System of

Measurement ?

Why Do We Need a System of

Measurement ?

Which would you prefer? 2lbs of gold or 1 kilogram of gold?

Which would you prefer? 2lbs of gold or 1 kilogram of gold?

2 lbs of Gold 1 kilogram of Gold

How do you know if you are getting the same amount as everyone else without a standard to compare it to?

A “standard” is something used as a comparison for measurement•2 Important factors for standards:

•Must be available for everyone and something in nature that is the same all over the earth•The standard must never vary

English System of Measurement

English System of Measurement

• The English System of Measurement is commonly used as the day to day system in the United States. – Pounds– Feet– Gallons

• But what are the standards for these units?– there are no standards in nature for

these units, the rest of the world has moved to another measurement system.

• The English System of Measurement is commonly used as the day to day system in the United States. – Pounds– Feet– Gallons

• But what are the standards for these units?– there are no standards in nature for

these units, the rest of the world has moved to another measurement system.

International System of Units (SI)• Modern Form of the Metric

System• Units of measurement

devised around 7 base units• Works on a scale of 10• Prefixes are used to

distinguish between base units

• Use of conversion factors

•

Know these SI prefixes: Know these SI prefixes:

109 106 100 10-6 10-91000 10

1

0.1 0.01 0.001

Conversion Factors: ratio of equivalent measurements

1 m = 10 dm

1 m = 100 cm

1 m = 1000 mm

SI Units of MeasurementSI Units of Measurement

Quantity SI Unit Symbol

Length Meter M

Volume Cubic meterLiter

m3

L

Mass Gram g

Density Grams per cubic

centimeter

g/cm3

An approximate comparison of the two

systems:

English System Metric System

1 yard 0.9 meter

1 mile 1.5 kilometer

1 pound 0.5 kilogram

1 quart4 quarts = 3.8 liters

~1 liter

There are exact conversion factors that can be used to change units in one system to units in the other. The table above might help you begin to visualize the size of the units of the metric system.

SIGNIFICANT FIGURESSIGNIFICANT FIGURES

Rule Examples

The following are always significant non zero digits zeros between non zero digits zero to the right of a non zero digit and left of

a written decimal finishing zeros to the right of the decimal

point

673 has 3506 has 31.009 has 457.00 has 4

The following are NEVER significant zeros to the left of the first non zero digit

0.67 has 20.004 has 1

EXCEPTIONS counting numbers Exact conversion factors

30 days in June100cm in 1m

LET’S TRY A FEWLET’S TRY A FEW

• a) 1.020 ________sig figs• b) 45.0 ________sig figs• c) 154 ________sig figs• d) 0.00003 ________sig figs• e) 54,000,000 ________sig figs

• a) 1.020 ________sig figs• b) 45.0 ________sig figs• c) 154 ________sig figs• d) 0.00003 ________sig figs• e) 54,000,000 ________sig figs

4

3

3

1

2