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

Alfred Ajibola - 07th February, 2019 @ 06:22 PM

Topics in Physics

Density and Specific Gravity Force and Motion - Newton's Laws of Motion Motion, Speed, Velocity and Acceleration Heat Transfer, Conduction, Convection and Radiation Concept of Heat and Temperature Gravity explained with some fun facts Zeroth Law of Thermodynamics - Thermal Equilibrium Fundamental Units, Derived Units; Similarities and Differences between Fundamental and Derived Units Physics - Basic and Fundamental Physics Concepts

Academic Questions in Physics

Please check out our Test Your Knowledge page to see all Questions and Answers

Consider this expression below:

A body X exerts a force FX on another body Y. In return, body Y exert a force FY back on body X. The forces FX and FY are equal in magnitude but opposite in direction.

Putting the above expression into equation:

FX = -FY

Where FX is the action force

FY is the reaction Force

The above expression relates to _____.

  • A. Theory of Force
  • B. Force Postulate
  • C. Einstein's proposal on Relativity
  • D. Newton's 1st law of motion
  • E. Newton's 2nd law of motion
  • F. Newton's 3rd law of motion

The tendency of a body to remain in a state of rest or in uniform motion is referred to as _____.

  • A. tension
  • B. uniform acceleration
  • C. constant acceleration
  • D. deceleration
  • E. inertia
  • F. velocity

A change in the position of an object with reference to time is best described as _____.

  • A. momentum
  • B. displacement
  • C. velocity
  • D. acceleration
  • E. direction
  • F. motion

The saying "what goes up on earth must come down" can be best attributed to _____.

  • A. force
  • B. motion
  • C. mass
  • D. acceleration
  • E. average velocity
  • F. constant velocity

We have _____ laws of Thermodynamics.

  • A. 1
  • B. 2
  • C. 3
  • D. 4
  • E. 5
  • D. 6

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.

Please read on Important concepts in Physics here.

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)

Please read on the Concept of Temperature and Heat here.

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).

Please read on Motion, Speed, Velocity and Acceleration here.

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)

You can read on Density and Specific Gravity here.


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.

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If there is a power surge, the fuse will break, preventing damage to the electrical devices. It will also prevent the incidence of 🔥 fire🔥 on/from such device.

Physics is one of the core sciences.

Physics is defined the scientific study of matter and the movement of matter through the space and time of the universe.

Understanding the basic and fundamental concepts of physics will help you better comprehend this subject. Below are some of the concepts:

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