# Fundamental Quantities and Units in Physics

### What are Units in Physics?

Anything that can be measured must have a unit of measurement. For instance, it isn’t right to say: 'I weigh 65'. Based on this fact, units are means of measurement. Anything measurable is termed a physical quantity.

The analogy below explains a physical quantity and its unit:

• Now, let's imagine you wish to buy uncooked rice at a local store around you. Understand that 'rice' is the physical quantity to be measured here. Before buying the specific quantity of rice you need, it has to be first measured. This could be 'one cup' for instance, before it is sold to you. In this case, 'one cup' is the unit of measurement, that is: the quantity of rice to be bought.

• Using the sport of boxing as another instance; we have different categories like feather weight, light weight and heavy weight. All of these categories are made possible because the mass (weights) of the individuals involved have been measured via a unit.

Fundamental and derived units are internationally recognized as units of measurement. This is why they are also called the Standard International units or SI units.

In physics, an understanding on fundamental and derived units are very important because the properties of physics are represented only by their units in equations.

### What are fundamental units?

Fundamental units are the units of fundamental quantities.

A fundamental unit is a unit that does not depend on any other unit; neither can it be changed nor is related to another fundamental unit.

A fundamental unit is also referred to as a basic unit.

Fundamental units are always constant. This means that they don't change, that is; they remain the same and are standardized all over the world. We have seven fundamental quantities alongside their respective units. They include:

1. Mass (m). Its unit is kilogram (kg)
2. Length (l). Its unit is meter (m)
3. Time (t). Its unit is second (s)
4. Temperature (T). Its unit is Kelvin (k)
You can read on the concept of temperature and heat here.
5. Electric Current (I). Its unit is ampere (A)
6. Amount of Substance (n). Its unit is mole (mol)
7. Luminous Intensity (|v). Its unit is candela (cd)

The table below shows the fundamental quantities with their symbols and the respective fundamental units (with their symbols): The seven fundamental units cannot be broken down into elementary or smaller unit. In short, they are the most basic units of measurement.

Although the fundamental and derived units are internationally recognized, some countries may still choose to use a different unit for measuring the same quantity. Regardless the unit that has been chosen, it must however, still be convertible to its respective fundamental or derived unit via a constant factor. For instance:

• The units yard and feet may be used to measure length; but meter still remains the fundamental unit of length.
• Similarly, while pounds may be used to measure mass, kilogram still remains its fundamental unit thus making it globally recognized and accepted as the basic, standard and fundamental unit for measuring mass. 