Physical Quantities and Units

The basic quantities and Units are the System International of Units, also called the SI units.

It makes up of 7 base quantities and units. They are as below

Base quantity Base Unit

Name Symbol Name Symbol

time t second s

length l metre m

mass m kilogram kg

temperature T,0 kelvin K

electric current I ampere A

amount of substance n mole mol

luminous intensity I_v candela cd

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These SI units are used very accurately all around the world

All other physical quantities are known as derived quantities. Both quantity and its unit are derived from a combination of base units by using a defining equation

For example, acceleration= change in velocity(m s-1) divided by time taken(s)

Combining the units in the defining equation gives us the derived unit of acceleration

For very large or very small numbers, we can use standard prefixed with the base units. The followings are the prefixes

Prefix Symbol Multiplier

giga G 10 to the power of 9

mega M 10 to the power of 6

kilo k 10 to the power of 3

milli m 10 to the power of -3

micro µ 10 to the power of -6

nano n 10 to the power of -9

pico p 10 to the power of -12

femto f 10 to the power of -15

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There might be errors in the experimental methods or equipment where readings are either too big or too small.

For example, if your newton-meter reads 0.2 N with no weights on it, then your measurement of force will always be 0.2 N too large

These are called zero errors