Why the MetricSystem is a good thing

HistoryHistory• Metric system created

to have a unified, universal system of measurement.

• In 1790 King Louis XVI of France assigned a group to begin this task.

• As of 2005, only three countries, the United States, Liberia, and Myanmar, have not changed over to the metric system.

The SI system is used universally for all scientific purposes so the metric system will be the only system of measurement we will be using in science this year.

The metric system was developed based on decimals. The base units are converted by factors of 10 by simply moving the decimal place. A prefix is then added to the base unit to indicate a larger or smaller unit.

The base unit for length is the meter. The meter was originally defined as 1/10,000,000th of the distance from the North Pole to the Equator through Paris. The meter is now defined as the distance traveled by light in an absolute vacuum in 1/299,792,458 of a second (don’t worry – you don’t have to remember this).

The base unit for mass in the metric system is the gram. Mass is a measurement of how much matter is in an object. Mass is measured using a balance. One gram is about the same as a small paper clip.

Double pan balance

Triple beam balance

Mass of about one gram

Volume is the measurement of how much space an object occupies. Liquid volume is measured with a graduated cylinder. Solid volume can be calculated with a formula or by water displacement. The basic unit for volume in the metric system is the liter. One liter sodas can be

purchased at convenience stores.

Water displacement

Graduated cylinder

Volume formula for a rectangular prism is length x width x height.

Temperature is the measurement of the heat of something on a scale. The basic unit of temperature in the metric system is Celsius or centigrade. Water freezes on the Celsius scale at 0° and boils at 100°. Temperature is measured with a thermometer.

Thermometer

Water at freezing point measured by a digital thermometer

The metric system uses prefixes added to the base unit to represent larger or smaller units. Each prefix is a multiple of 10.

Prefix Abbreviation Word value Number value

kilo km one thousand

1000

hecto hm one hundred 100

deka dam ten 10

deci dm one tenth 0.1

centi cm one hundredth

0.01

milli mm one thousandth

0.001

Length Units in Metric System

kilometer

hectometer

dekameter

meter

decimeter

centimeter

millimeter

Most Common Volume Units in Metric System

liter

milliliter

Most Common Mass Units in Metric System

kilogram

gram

milligram

• The idea – to express error in measurement.

• You get significant figures by measuring a value and then estimating one degree beyond the limit of the reading

• Example -if an object, measured with a ruler marked in millimeters, is known to be between six and seven millimeters and can be seen to be approximately 2/3 of the way between them or a little more than half way, an acceptable measurement for it could be 6.6 mm or 6.7 mm.

• The .6 or .7 is estimated – these digits are uncertain.

• The 6 millimeters is known – these digits are certain.

• By using significant figures correctly, you are increasing the accuracy of your measurements.

• In the example from above, if the object measured with a ruler in millimeters was exactly on 6 millimeters, then to show significant figures you would express the measurement as 6.0 millimeters.

Degree of Uncertainty in Measurement

Precision vs. Accuracy

• Precision: A degree of agreement among several measurements of the same quality.

• Accuracy: Is the agreement of a particular value with the true value

Metric mass can be expressed in terms of metric volume. One gram of mass equals one milliliter in volume. One milliliter equals one centimeter cubed.

If one milliliter equals one gram then 1000 milliliters or 1 liter equals 1000 grams or 1 kilogram.

kilogram/liter

A meniscus (from the Greek for "crescent")

•is a curve in the surface of a liquid

• produced in response to the surface of the container or another object.

•water and glass.

•When measuring liquids you will have to keep in mind significant figures while reading the bottombottom of the meniscus.

The volume of the liquid using significant figures is 40.76 mL.