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#### Prefixes in the Metric System

One of the wonderful things about the metric system is its use of prefixes. Prefixes as you know, are short word segments placed at the beginning of words to modify them. In common usage, for example, a prefix like uni- (meaning one), is used in unicorn, unicycle and Universe. Another common prefix is tri- (meaning three) as in tricycle, triangle and trimester.

In the metric system, prefixes are placed in from of standard units of measurements to make them bigger or smaller. We will discuss the use this method for measurements of distance, mass, and volume. However, the same prefixes may be used in a wide variety of other scientific measurements. For example, you will come across terms like millivolts, centipede, kilowatts, and so on.

Below is a table of the prefixes we use in the LabLearner program, although deci- is not used very often.

#### Things That Are Measured In: Kilometers (km)

A kilometer (km) is 1,000 meters. Kilometers are used to measure fairly long distances. In the English system of measurement, distances like these are typically measured in miles. Therefore, you would not report the hight of your kitchen table in kilometers. When you go for a drive or take a trip, you can think in terms of kilometers.

Very large distances are also reported in kilometers. Thus, the distance from the Sun to the furthest planet, Neptune, is about 4,491,100,000km or in words; four billion, four hundred and ninety-one million, one hundred thousand kilometers. Very often, distances of this size are reported in scientific notation. For example, the distance from the Sun to Neptune could be reported as 4.491 X 109. We will not measure numbers so large or small in LabLearner Metric Lab that we will need to use scientific notation.

The following are the types of things that would commonly be reported in kilometers:

#### Things That Are Measured In: Meters (m)

Meters (m) are the standard unit of length in the metric system. We just discussed things bigger than a meter when we talked about kilometers. We typically use meters when talking about things larger than ourselves up to several hundreds of meters. Larger than that, we switch to kilometers.

On the smaller side, when we think of things much less than a meter, we usually report them in centimeters or millimeters. We will talk more about centimeters and millimeters in a moment.

The following are the types of things that would commonly be reported in meters:

Also, all international sports use the metric system of measurement for distance, height and length. Not surprisingly then, all Olympic sports report results in kilometers (kg), meters (m) and centimeters (cm).

#### Things That Are Measured In: Centimeters (cm)

Centimeters are probably the unit most often used in LabLearner. This is simply because most experiments are performed on a lab bench or similar table. Therefore, items on the bench are typically (but not always) smaller than a meter. As a general rule, we will use centimeters when making measurements less than a meter.

We often report centimeters as decimals, that is fractions of centimeters. For example, 10.5 cm. The number to the right of the decimal point is actually the number of millimeters (discussed further below). Thus, 10.5 cm is the same as saying “ten centimeters and five millimeters”. However, we would simply say “ten point five centimeters”.

We will talk a bit more about millimeters in a moment. Below are example of things that are likely to be recorded in centimeters:

#### Things That Are Measured In: Millimeters (mm)

Although millimeters are a long, long way from the smallest thing scientists can measure, they are the smallest unit we can use in LabLearner. A millimeter is one one-thousandth of a meter (1/1000 m or 0.001 m). While that seems pretty small, about 20 average-sized human cells would fit end-to-end in a millimeter! The smallest marking on a meter stick is a millimeter. Therefore there are 1,000 of these markings on every meter stick.

There are many important things in science that are much, much, much smaller than a millimeter. Water molecules (H2O), for example are several millions times smaller than a millimeter. And atoms are even smaller than molecules! Therefore, atoms and molecules are not in the visible world. In the visible world, millimeters and fractions of millimeters are the extent of our ability to see with the naked eye and easily measure.

Below are examples of things that are often measured in millimeters: