Units - LeFonch

What are Units?

Units are used to measure certain things. For example meters are used to measure distance and joules are used to measure work.

There are seven fundamental S.I. units. All other units are derived from these.
Other units of measurement are made from different combinations of fundamental units.
Below is a list of the names of the units alongside their symbols.
Mass: kilograms - kg
Length: meters - m
Time: second - s
Temperature: Kelvin - K
Amount of Substance: moles - mol
Electric current: amperes or amps - A
Luminous intensity: candela - cd
S.I. units, and the entirety of the metric system are designed to be consistent and reasonable and are used internationally.
Even in countries like the United States where the imperial system is more common, the metric system is still used in scientific studies and research.

Kilograms define the mass of an object.
Kilograms are generally used over grams (which is the base unit) due to most objects generally weighing a few kilograms or more.
Mass is independent of gravitational force and should not be confused with weight, which is a separate measurement.
Generally tonnes are used to notate 1000 kilograms. These shouldn't be used with the imperial tons which notate a slightly different mass (1 metric tonne ≈ 1.1 imperial tons).
For consistency, megagrams can be used instead of tonnes as they both mean the same thing (and frankly "megagram" sounds a lot cooler).

Meters are units designed to measure distance. The average adult is usually around 1.7 meters tall.
Meter's are based around the circumference of the Earth. The Earth's circumference is almost exactly 40,000 meters (there is a small discrepancy due to measurements when meters were first defined).

Seconds are used to measure the passing of time.
Time is one of the few measurements to use somewhat irregular units.
Each step up is by 60, instead of by 10.
This only applies to hours (60 min or 3600s) and minutes (60s).
Scientific prefixes can still be used but you will see hours and minutes a lot more often.

Kelvin is the measurement of temperature.
It is similar to Celsius and increases or decreases proportionally to Celsius.
Celsius and Kelvin rise with the same increments, although 0 Kelvin is -273.15 Celsius.
Kelvin and Celsius can be inferred from one another by either adding or subtracting 273.15 Celsius.
Temperature is based on the movement of atoms, with more heat making atoms vibrate more and vice versa.
Absolute zero, or 0 Kelvin is when there is no heat vibration at all.

Moles are a very large number, similar to a dozen or a pair.
For example you could have a mole of bread like how you could have a dozen loaves of bread.
Moles are used to represent the amount of particles in an amount of substance.
Moles are important as other units such as kilograms or liters can't objectively measure the amount of substance because of the different densities and masses of substances.
One mole is 6.022 • 10²³ particles (a reaaaaaaaally big number).

Electric current is used to connect electric phenomena (such as electric and magnetics) with mechanical forces.
Electric current is the flow of charged particles through a conductor.
Amperes and electric current shouldn't be confused with volts, which measure electric potential difference.

Candelas are used to measure luminous intensity. In other words they are the unit for the measurement of light.

When notating other units, square brackets can be used.
For example [v], would mean the unit of velocity, which is m/s or meters per second.
In a scenario where larger units are needed, [v] = km/h would explain what velocity is.
Although units generally always should be changed into the SI units.
Thus it could be written as: [v] = 1000m/3600s.

Prefixes can be added in front of units in order to show the amount, depending on if you're measuring larger or smaller quantities.
For example kilo means 1000, thus a kilometer is 1000 meters.
Below is a chart of all necessary metric prefixes. There are some additional ones but they are too miniscule to care about unless its specifically related to your field of study.

For perspective, the nucleus of an atom is usually several femtometers, depending on the size of the atom.