Physical quantities and measurements

Physical quantity

A physical property of a body or substance that can be quantified by measurements

SI unit of length

Metre (m)

SI unit of mass

kilogram (kg)

SI unit of time

second (s)

SI unit of electric current

Ampere (A)

SI unit of amount of substance

Mole (mol)

SI unit of luminous intensity

Candela (cd)

derived units

Defined in terms of the seven base quantities via a system of quantity equations

Volume

m^3

Density

kg m^-3

Velocity

m s^-1

Acceleration

ms^-2

Force

Newton (N) m kg s^-2

Energy and work

Joule (J) m^2k kg s^2

Power

Watt (W) m^2 kg s^-3

Frequency

Hertz (Hz) s^-1

Electric potential difference, electromotive force

Volt (V) m^2 kg s^-3 A^-1

Electrical resistance

ohm m^2 kg s^-3 A^-2

Quantity of charge

Coulomb (C) sA

nano (n)

10^-9

Micro (u)

10^-6

Mili (m)

10^-3

Centi (c)

10^-2

Deci (d)

10^-1

Kilo (k)

10^3

Mega (M)

10^6

Giga (G)

10^9

Precision

Reproducibility; close to other values obtained by repeating the determination using the same procedure

Accuracy

Correctness; close to true value

Error

Anything that causes measurement to differ from true value

More precise instrument

Can measure smaller intervals, values given are likely to be closer together

Random error

Error that occurs inconsistently each time a measurement is repeated

Systematic error

Error that occurs consistently each time measurement is repeated

Positive zero error (vernier calipers)

Right of main scale

Negative zero error (vernier calipers)

Left of main scale