SI Units and Symbols



Every type of quantity measure in SI has a base unit and a symbol for that unit. These names and symbols are shown in the metric system. All other SI units can be derived from these seven basic units.



LENGTH



The word length is used in many different ways. For example, the length of a novel is the number of pages or words it contains. In scientific measurement, length is the distance between two points. That distance may be the diameter of a period on this page or the distance from Earth to the moon. The SI base unit of length is the meter(m). A baseball bat is about 1 meter long. Metric rulers and metersticks are used to measure length.

Recall that measurement in SI is based on powers of ten. The prefix deci- means 1/10, so a decimeter is one-tenth of a meter. Similarly, a centimeter(cm) is one-hundreth of a meter. The diameter of a shirt button is about 1 cm.

                      100 cm = 10 dm = 1 m

Centimeters can be divided into smaller units called millimeters (mm). A millimeter is 1/1000 of a meter. One tooth along the edge of a postage stamp is about 1 mm long.



Choosing a Unit

The size of the unit you use to measure with will depend on the size of the item being measured. For example, you would us the centimeter to measure the length of your pencil and the meter to measure the length of your classroom. What unit would you use to measure the distance from your home to school?



find the rest of the article on www.glencoe.edu/physicalscience