# Fundamental Quantities and Units in Physics

#### Academic Questions in PhysicsPlease check out our Test Your Knowledge page to see all Questions and Answers The Law of Inertia is also referred to as _____. A. 1st Law of Thermodynamics B. 2nd Law of Thermodynamics C. 3rd Law of Thermodynamics D. Newton's 1st Law of Motion E. Newton's 2nd Law of Motion F. Newton's 3rd Law of Motion The process whereby the velocity of an object increases and decreases over a period of time is best associated with the term _____. A. Speed B. Velocity C. Momentum D. Constant Velocity E. Acceleration F. Average Velocity The rate of motion is best referred to as _____. A. Speed B. Velocity C. Momentum D. Inertia E. Acceleration F. Constant Velocity 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

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### 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:

• Let’s imagine you wish to buy uncooked rice in a local store around you. (Rice is the physical quantity to be measured here). Before you buy the specific quantity of rice; it's first measured (let’s say "one cup" for instance) before it's sold to you. In this case, "one cup" is the unit of measurement (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 Unit (SI Unit).

Please read on Derived Units, its Similarities and Differences with Fundamental Units here.

Note: In physics, understanding 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.

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

Fundamental Units are always constant. This means that they don't change, (remains the same) and are standardized all over the world. The fundamental quantities alongside their respective fundamental unit are 7 in number. They include:

1. Mass (m) is a fundamental quantity whose unit is kilogram (kg)
2. Length (l) is a fundamental quantity whose unit is meter, (m)
3. Time (t) is a fundamental quantity whose unit is second (s)
4. Temperature (T) is a fundamental quantity whose unit is Kelvin (k)
You can read on the Concept of Temperature and Heat here.

5. Electric Current (I) is a fundamental quantity whose unit is ampere (A)
6. Amount of Substance (n) is a fundamental quantity whose unit is mole (mol)
7. Luminous Intensity (|v) is a fundamental quantity whose unit is candela (cd)

The table below shows the fundamental quantities (with their symbols) and the respective fundamental units (with their symbols): The above (7 fundamental units) cannot be broken down into elementary or smaller unit. In short, they are the most basic units of measurement.

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 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. 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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