Fundamental Units, Derived Units; Similarities and Differences between Fundamental and Derived Units

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”.

Units are means of measurement. Anything measurable is a physical quantity. Consider this analogy:

In the local stores around you, let’s imagine you wish to buy rice. (Rice is the physical quantity to be measured here).

Before you buy a quantity of rice; it's first measured (let’s say one derica for instance) before it is sold to you. In this case one derica is the unit of measurement (quantity of rice to be bought).

In the sport of boxing, 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 sometimes called the Standard International Unit (SI Unit).

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

Fundamental Units

A fundamental unit (also called a Basic Unit) is a unit that does not depend on any other unit; neither can it be changed nor is related to another fundamental unit.

Fundamental Units are constant (remains the same) and standardized all over the world. We have seven of them. They include:

• Mass (Kilogram, Kg)

• Length (Meter, m)

• Time (Seconds, s)

• Temperature (Kelvin, k)

• Electric Current (Ampere, A)

• Amount of Substance (Mole, mol)

• Luminous Intensity (Candela, cd)

The above (7 fundamental units cannot be broken down into elementary or smaller unit. In short, they are the most basic unit.

Note: 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, whatever unit has been chosen, it must however, still be convertible to the 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 the fundamental unit of mass).

Derived Units

Derived units are units that are dependent on fundamental units and can be expressed in terms of fundamental units.

As the name imply, derived units are always derived from fundamental unit. For instance, velocity is a quantity whose derived unit is meter per second (m/s). It is derived from distance and time (Distance is a function of the fundamental unit length while time is another fundamental unit).

Note: Since derived units are always derived from fundamental units, we cannot have "feet per second" as the unit of velocity (even though "feet" can still be used to measure length).

Examples of some derived units include:

• Velocity (m/s)

• Density (Kg/m3)

• Force (mass x acceleration, Kg/s2 or N)

• Power (W)

Similarities between fundamental and derived units

1. Both are used to express physical quantities.

2. Both are standardized International System of Units (SI Units).

Differences between Fundamental and derived units

1. Fundamental units are independent of every other unit including themselves while derived units are dependent on fundamental units.

2. Fundamental units cannot be further broken down while derived units can be broken down.

3. We have only 7 fundamental units while derived units are much more in number.

4. Fundamental units are uniquely expressed while derived units are expressed in terms of fundamental units. Alfred Ajibola is a Medical Biochemist, a passionate Academician with over 7 years of experience, a Versatile Writer, a Web Developer, a Cisco Certified Network Associate and a Cisco CyberOps Associate.