Physics

Fundamental Quantities and Units in Physics

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

Topics in Physics

Derived Units: Similarities and differences with fundamental units Gravity: Facts on Gravity Relative Density of Substances and Specific Gravity Types of Heat Transfer: Conduction Types of Heat Transfer: Convection Types of Heat Transfer: Radiation Physics Scheme of Work, SS1, First Term Physics Scheme of Work, SS1, Second Term Physics Scheme of Work, SS1, Third Term Velocity and Acceleration Newton's Laws of Motion Importance of Gravity What is Density? Density of various substances Concepts of Force and Motion in Physics Motion and Speed in Physics Concept of Heat Transfer Concepts of Heat and Temperature What is gravity? Concept of gravity on the solar system Zeroth Law of Thermodynamics: Thermal Equilibrium Fundamental Quantities and Units in Physics


Academic Questions in Physics

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Which of the following is a fundamental quantity?

  • A. Luminous Intensity

  • B. Area

  • C. Volume

  • D. Velocity

  • E. Concentration

  • F. Acceleration

An object at rest will temporarily stay in its state of rest, and if the object is in uniform motion, it will temporarily move in a straight line, unless an external force acts upon it.

The above statement refers to Sir Isaac Newton's first law of motion.

  • A. True

  • B. False

Which of the following statement is incorrect concerning gravity?

  • A. The force of gravity is generally considered the strongest force among the four forces that govern the universe

  • B. Your weight changes as you travel away from the earth

  • C. If we dig the earth until we get into its center, we will have no weight as a result of lack of gravity

  • D. Gravity prevents us from falling off the constantly rotating earth

  • E. If a hammer and a feather are dropped simultaneously in a vacuum, they will both land at the exact same time as a result of gravity

  • F. Weight is always a function of gravity

Isaac Newton Hit by Apple - Len Academy

Sir Isaac Newton was hit by an apple when he pondered on force, motion and gravity.

  • A. True

  • B. False

The movement of gaseous particles through a tiny hole is termed _____.

  • A. Osmosis

  • B. Diffusion

  • C. Effusion

  • D. Infusion

  • E. Defusion

  • F. Gaslusion

A lighted bulb transfers heat through a process termed _____.

  • A. Conduction

  • B. Convection

  • C. Radiation

  • D. Oxidation

  • E. Reduction

  • F. Electrical Induction

A measurement of how much the velocity of an object changes with time is termed _____.

  • A. Displacement

  • B. Acceleration

  • C. Speed

  • D. Momentum

  • E. Velocity-Time graph

  • F. Average velocity

Which of the following differentiates velocity from speed?

  • A. Distance

  • B. Time

  • C. Momentum

  • D. Inertia

  • E. Direction

  • F. Distance and Time



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.

Please read on important concepts in physics here.


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.
    Please read on the concept of mass and weight here.


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.

Please read on derived units, its similarities and differences with fundamental units here.


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.

You can read on molecular mass explained with worked examples here.


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):

Fundamental Units - Len Academy

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.

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Amazing facts in Physics

Marie Curie was the first person ever to win two Nobel prizes. She won her first Nobel price for physics in 1903, and the second for chemistry in 1911 for her work on radioactivity.

The hottest temperature ever recorded occurred in Furnace Creek Ranch, Death Valley, California, USA, at 56.7oor (134oF) on July 10, 1913

Elephant on cumulus cloud - Len Academy

A medium-sized cumulus cloud has a weight of about 80 adult elephants.

You can think of cumulus cloud as a detached, individual, cauliflower-shaped cloud often seen in fair weather conditions

Leaning Tower of Pisa - Len Academy

The reason the Leaning Tower of Pisa is tilted is the same reason it's still standing

One quarter of an apple is filled with air and that's why they float in water

Alfred Noble - Len Academy

The Nobel price was named after its founder, Alfred Noble. He is a Swedish, born on October 21, 1833; and was the inventor of dynamite. He was also a a famous scientist and a successful business man.

Glass Ball - Len Academy

Glass balls bounce higher than rubber balls

Every planet has its own unique gravitational force. For instance, Mars has a gravity of 3.711 m/s2 while earth’s gravitational force is 9.807m/s2.

When two metals are put together in space, they will stick together as if they are welded. This phenomenon is called cold welding

The fastest animal on land is cheetah. It can reach a maximum speed of about 113km per hour.


Notable points in Physics

The Standard International (SI) unit for density is kilogram per cubic metre (Kg/m3).

The table below shows various substances with their densities:

Substance

Density (Kg/m3)

Helium

0.179

Air (1atm and 20oC)

1.20

Bamboo Wood

400

 Ethanol

810

Methylated Spirit

800

Benzene

900

Paraffin Wax

900

Ice

920

Water (Fresh Water)

1000


Please read on density here

Force can be balanced or unbalanced.

When forces from different directions act on an object and consequently bring about the object's motion, then such forces are unbalanced.

Conversely, if theses forces bring about zero motion (static position or no movement) on the object of reference, then it's a balanced force.

In summary,

  • An apple hanging on a tree (without any form of movement) has a balanced force.

  • An apple falling from a tree has an unbalanced force.

If one covers a distance of 10,000 meters in 50 seconds and another covers the same distance in 5,000 seconds, we can conclude that the first person has a greater speed because he covered the same distance at a lesser time.

  • Speed is defined as distance travelled per unit of time. It can also be defined as the rate of change of distance.

Speed = distance/Time

Speed is a scalar quantity since it has only magnitude. Speed does not have a direction.

In physics, motion is defined as a change in the position of an object with reference to time.

Although we sometimes sit or stand in a fixed position, that doesn’t mean motion isn’t taking place. The fact that the earth is constantly rotating implies that we are indirectly moving along with it. We can thus say that motion can be relative to some frame of reference.

In the above paragraph, the earth (constantly rotating along its axis) is our frame of reference and everything present on earth is in motion (with regard to earth as a frame of reference).

Please read on the concepts of motion and speed here

Heat is a form of energy. It cannot be lost according to the first law of Thermodynamics; rather it will be transferred. The first and second laws of thermodynamics are stated below:

  • Energy can neither be created nor destroyed but can be transformed or converted from one form to another.

    1st law of thermodynamics


  • In the course of energy transfer, some energy is lost in the form of heat to the surroundings.

    2nd law of Thermodynamics

Please read on the concept of heat transfer here