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## MEASUREMENTS

How big is an ant? How high is a mountain? An observation of a property (characteristic) as a number on a scale of units is a measurement. A child’s height may be measured on a measuring tape as 4 ft (1.2 m).

## WHAT IS A MEASUREMENT SCALE?

A simple measurement scale is a series of numbered graduations (marks) on a measuring instrument. Modern electronic instruments often have digital readouts that automatically display the reading.

## WHO MADE THE FIRST MEASUREMENTS?

Early people used measurements to build structures such as Stonehenge and the pyramids. Many measurements from this time were based on parts of the body—for example, a cubit was the distance from the elbow to the tip of the outstretched hand.

## HOW ARE MEASUREMENT UNITS FIXED?

Units are fixed by international agreement. Scientists define a standard against which scales can be calibrated (set and checked). The standard kilogram is the mass of a platinum-iridium cylinder kept in Sèvres, France. The meter is defined as the distance traveled by light in 1/299,792,458 of a second.

Table 22. MEASUREMENT UNITS

QUANTITYUNIT NAMESYMBOL
Base units
Masskilogramkg
Lengthmeterm
Timeseconds
Electric currentampere (amp)A
TemperaturekelvinK
Derived units
Areasquare meterm2
Volumecubic meterm3
Densitykilogram per cubic meterkg/m3
Speedmeter per secondm/s
Accelerationmeter per second squaredm/s2
ForcenewtonN (kg m/s2)