1.3 The Units of Measurement

units

standard quantities used to specify measurements

Imperial system

a measurement system

metric system

the system of measurements used in most countries in which the metre is the unit of length, the kilogram is the unit of mass, and the second is the unit of time

International System of Units

(SI) the standard unit system used by scientists, based on the metric system

metre (m)

the SI standard unit of length, defined as the distance light travels through a vacuum in 1/299,792,458 seconds

kilogram (kg)

the SI standard unit of mass, defined as the mass of a block of metal kept at the International Bureau of Weights and Measures at Sèvres, France

mass

a measure of the quantity of matter making up an object

weight

a measure of the gravitational pull on the matter of an object (measured in newtons (N))

second (s)

the SI standard unit of time, defined as the duration of 9,192,631,770 periods of the radiation emitted from a certain transition in a caesium-133 atom

kelvin (K)

the SI standard unit of temperature

temperature

a measure of the average kinetic energy of the atoms or molecules that compose a sample of matter

Celsius scale (°C)

the temperature scale most often used by scientists (and by most countries other than the USA), on which pure water freezes at 0°C and boils at 100°C (at atmospheric pressure)

prefix multipliers

multipliers that change the value of the unit by powers of 10

conversion factor

a factor used to convert between two different units; conversion factor can be constructed from any two quantities known to be equivalent

dimensional analysis

the use of units as a guide to solving problems

derived units

a unit that is a combination of other base units (ex: the SI unit for speed is metres per second, a derived unit)