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Science Investigation Measurement

By Thomas Moorman
John Wiley & Sons, Inc.

Measurement is a most important part of the sciences. Not only do scientists use measuring instruments of many kinds, they also have been in the forefront of developing new measuring tools and standards.

SI Units

While some countries continue to use their own customary measuring units (in the United States we use pounds, feet, gallons, and so on), the International System of Units (SI Units, from the French Systéme International) has been adopted worldwide for both commercial and scientific purposes. The basic SI units include the following:

• Meter: length or distance
• Kilogram: mass, more commonly called "weight"
• Second: time
• Ampere: electric current
• Candela: light and other radiation
• Mole: comparing other substances to the molecular weight of a certain form of carbon
• Kelvin: temperature

From these basic units come many "derived units." An example is the measurement of area, for which the unit, called the square meter, is derived from the basic length unit or meter. Another example is the measurement of velocity, commonly called "speed" for which the unit, called meters per second, is measured from the basic meter traveled.

How to Measure

To measure something usually means taking a widely accepted tool, such as a meter stick, and comparing it with the thing to be measured. Practical measuring methods abound, ranging from astronomers' methods for estimating the Earth's distance in light-years from celestial objects to micrometers and other tools used for measuring very small objects. Scientists are even finding ways to measure the sizes of atomic particles, their "spin," and other characteristics.

For this discussion of measurement, the metric system will be used in all examples. If you have a meter stick at hand for reference it will be useful. If you do not have one, the commonly available foot ruler with a metric scale along one side (about 30 centimeters, each divided into tenths or millimeters) will do.

Let's say that you want to measure the width of a room with a meterstick. You agree to measure it to the nearest millimeter (or 0.001 meter). If you are not familiar with measuring in the metric system, note that a millimeter is equal to roughly 1/32-inch.

If the room you are measuring has a hard floor, you can make a pencil mark at the end of the meter stick each time you lay it out across the room. Or, if there is a carpet, you can stick a pin in it to mark the end of the stick. Let's say that you find there are five whole meters and a part of a meter that looks like figure 10.1 at the arrow point. This would read 5.823 meters.

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