Physics

Derived Units: Similarities and differences with fundamental units

len Alfred Ajibola - Wed, 26th February, 2020 @ 5:00 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

Please click here to see all Questions and Answers

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

FA = -FB

FA is the action force while FB is the reaction force.

The above statement expresses _____.

  • A. Force and Acceleration

  • B. Force and Gravity

  • C. Force and Momentum

  • D. Newton's first law of motion

  • E. Newton's second law of motion

  • F. Newton's third law of motion

A natural force that pulls a body towards the center of the earth is termed _____.

  • A. Centripetal force

  • B. Centrifugal force

  • C. Black hole

  • D. Average acceleration

  • E. Gravity

  • F. Momentum

A Greek letter that expresses density is _____.

  • A. Alpha_d

  • B. Beta_d

  • C. Theta_d

  • D. rho

  • E. dho

  • F. dhr

A glass of water has a higher density than an exact glass of oil.

  • A. True

  • B. False

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

  • A. True

  • B. False

Force is a quantity measured in _____.

  • A. Kilogram

  • B. Gravity

  • C. Incandescence

  • D. Meter per second square (ms-1)

  • E. Mole

  • F. Newton


What are Derived Units?

Derived units are the units of derived quantities. They are dependent on fundamental quantities and are expressed from the combination of two or more fundamental units.

Please read more on the concept of unit and fundamental units here. This knowledge is necessary.


As the name implies, derived units are always derived (from fundamental units). For instance, velocity is a quantity whose unit is derived from length and time (both of which are fundamental quantities) as summarized in the paragraph below.


  • Length (which could also mean distance) is a fundamental quantity measured in meters (m) while time is another fundamental quantity measured in seconds (s). To this end, the unit of velocity is meter per second (m/s) since it is derived from the fundamental units (length and time) respectively.
  • Please read on Newton's laws of motion here.


Since derived units are always derived from fundamental units, we cannot have 'feet per second' as the unit of velocity. This is because the unit feet isn't the ideal measurement for length (or distance); although it may be used as a unit of measurement in some cases.

You can read on motion and speed here.


Below are examples of some derived quantities and their units:


The diagram below shows some derived quantities, their respective derived unit and the unit's symbol. For instance, the first derived quantity from the table is 'area'. The derived unit for area is meter square (or square meter) whose symbol is m2.


Derived Units - Len Academy


It is important to state that the unit of area (m2) is derived from length. Meanwhile, recall that length is a fundamental unit.

You can read on basic and fundamental physics concepts here.

 

Similarities between fundamental and derived units

  1. Both units are used to express physical quantities.

  2. Both are recognized as the Standard International System of Units (SI Units).

You can read on heat transfer by conduction here.

 

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 seven 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.

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Amazing facts in Physics

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

If we have water of 100OC  in an aluminium cup whose temperature is the same as that of its surrounding; let’s say 22OC; We will observe the followings:

  1. The temperature of water inside the aluminum cup will begin to decrease from its initial 100OC.

  2. The temperature of the aluminium cup will increase from its previous 22OC.

  3. After some time, the temperature of the water, aluminium cup and the surrounding will become the same.

From the above instance, it can be deduced that the heat present in the water molecules are first transferred to the aluminium cup and subsequently to the surrounding.

Heat from water >> Aluminium Cup >> Surrounding

Meanwhile, understand that aluminium is a metal; and metals are good conductors of heat.

Eventually, the system (water and aluminum cup) together with the surrounding reaches the same temperature; and the heat transfer ceases. It is at this point that the water, aluminium cup and the surroundings are said to have reached a thermal equilibrium.

Please on the concept of heat and temperature here

Heat is never static. It is always transferred and thus: an object will increase its temperature by gaining heat energy from its surroundings while another object will simultaneously decrease its temperature by losing its heat energy to the surroundings. For this reason, we may also define temperature as:

The measure or ability of an object or substance to transfer heat energy to another object or substance.

The higher the temperature, the greater the ability of an object or substance to transfer heat. Conversely, the lower the temperature, the greater the tendency of an object to receive the transferred heat.

The point is: 'for heat to be transferred, we must have systems or objects or substances with varying temperatures

The earth is governed by the force of gravity and that’s why everything present on it (humans, plants, animals and even air) is always drawn towards it. You will actually need some form of force greater than gravity in order to pull yourself away from the earth.

As an instance, the earth as we know is spherical in shape and held in space. Also, all humans live on a constantly rotating earth and not inside the earth. Since we live on a spherical earth held in space, how come humans are yet to fall off the constantly rotating earth?

Well, the answer is gravity. Even if we attempt to jump off the earth into space, the force of gravity present on earth will still pull us down. In fact, in order to leave the earth; there has to be a force stronger that gravity; which must be applied to whatever is attempting to leave the earth. For this reason:

Whenever one jumps, a certain amount of force is needed to be applied by that person. However, gravity still return the person back to earth because the applied force had been exhausted.

Please read more on the concept of gravity here.

The larger the size of an object, the greater it’s force of gravity. Gravity is therefore affected by the size and closeness of objects.

Since the earth is larger than the moon, it will have a greater gravitational force than the moon. We will be more attracted on the earth than we would on the moon if we were astronauts on the moon. This implies that we will weigh differently on both places. For this reason, our weight will also vary on the various planets (because they are of different sizes). This is shown in the diagram below:

Weights on planets - Len Academy

Weight depends on the degree at which the gravity on earth or moon or another planet pulls an object while the Mass of any object or body will always remain the same (constant) since it’s the amount or quantity of matter in the body.

Please read on mass versus weight here

Zeroth Law - Len Academy

To better understand the Zeroth Law of Thermodynamics, we need to know what thermal equilibrium is. This is explained below:

Two bodies A and B are said to be in thermal equilibrium if each body can transfer heat to each other when placed closed together but ended up not transferring any heat to each other.

This will mean that both bodies are at equal temperature.

Now, according to the zeroth law, assuming we have three bodies namely X, Y and Z:

If X = Y and Z = Y, then X = Z

From the above expression, it will be observed that: if X and Y are in thermal equilibrium and Z and Y are in thermal equilibrium, therefore, X and Z must be in thermal equilibrium too.

So we can see that according to the zeroth law, temperature is a quantity worth measuring.

It can therefore be said that temperature is the quantity that remains constant (the same) for all systems in thermal equilibrium.

Consequently, the zeroth law of Thermodynamics states that if two separate bodies are in thermal equilibrium with another body, then they are also in equilibrium with each other

Please read more on the zeroth law of thermodynamics here