CH 104: Lesson 1a

Length

Meters and their derived units, such as kilometers, centimeters, and millimeters, all measure the property that we call length.

In the metric system, the basic unit of length is the meter. It is about the same as a yard. However, if you want to measure the distance between cities, the meter is too small. You wouldn't measure the distance to Portland in meters any more than you would measure it in yards. You need a larger unit. The metric system deals with different sized units by using prefixes.

Prefixes

The appropriate metric unit for distances between cities is a kilometer (km). That prefix, kilo-, means that we're talking about a unit that is 1,000 times larger than the basic unit of a meter. Thus a kilometer is 1,000 times the length of one meter.

If you do know how many meters it is between here and Portland, it's very easy to figure the distance in kilometers (divide by 1,000). That is much easier than with English units. In the metric system, the conversions are by factors of ten.

Sometimes a meter is too large a length for convenience. We have several smaller units. The two most common are the centimeter and the millimeter. The prefix centi- means "1/100th of", so a centimeter is 1/100th of the length of a meter. Therefore, there are 100 centimeters in one meter. Similarly, milli- means "1/1,000th of", so a millimeter is 1/1,000th of a meter. Therefore, there are 1000 millimeters in one meter.

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