Relative Density of Substances and Specific Gravity

len Alfred Ajibola - Mon, 27th January, 2020 @ 11:41: AM

Topics in Physics

Derived Units: Similarities and Differences with Fundamental Units Gravity: Interesting 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 Motion and Speed Concept of Heat Transfer Concepts of Heat and Temperature Gravity: What is Gravity? Zeroth Law of Thermodynamics - Thermal Equilibrium Fundamental Quantities and Units in Physics

Academic Questions in Physics

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

The rate of change of momentum is proportional to the applied force and will take place in the direction of that force.

The above statement is attributed to _____.

  • A. Albert Einstein

  • B. Isaac Newton

  • C. Galileo Galilei

  • D. Neils Bohr

  • E. Ernest Rutherford

  • F. Marie Curie

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



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Relative Density | Specific Gravity:

Density is an important unit of measurement. This is so because equal volumes of different substance have got their respective masses and weights.

Please read on the Concepts of Mass and Weight here.

Density is simply defined as the mass of a unit volume of a material or substance.

Note: An understanding on Density will aid you to better comprehend the concept of relative density.

Please read more on Density here.

Relative density involves the density of one substance in relation to that of water (at 4oC). it's also called specific gravity.

The Relative Density (R.D) of a material is the ratio of it's density (the material) to that of water at 4oC.

By principle, an object with a specific gravity or relative density of less than 1 will float on water, while that with value greater than 1 will sink in water.

Please read on the Molar Mass and its Calculations here.

Below is a summary of formulas for calculating Relative Density:

Relative Density - R.D = Mass of Substance/Mass of Water at 4oC

R.D = Weight of Substance/Weight of Water

R.D = Density of Substance/Density of Water at 4oC

R.D = ρsubstance / ρreference (water at 4oC)

Where ρ = Density

Note: Relative Density has no Standard International (SI) unit.

You can read on Molecular Mass and Relative Molecular Mass here.

The table below shows the Relative Density of some substances:



 Balsa Wood


 Oak Wood


 Ethanol (C2H5OH)


 Liquid Paraffin


 Olive Oil


 Coconut Oil




 Water (Fresh Water)


 Salt Water (Reef Aquarium)





 1.9 – 2.3

 Common  Salt (NaCl)


 Aluminium (Al)




 Iron  (Fe)


 Copper (Cu)


 Lead (Pb)


 Gold (Au)


 Osmium (Os)


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Amazing facts in Physics

Glass Ball - Len Academy

Glass Balls actually 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.

Please read on gravity here

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.

Please read on motion, speed, velocity and acceeration here


The Classical Mechanics (Laws of Motion) is a fundamental part of Physics.

Below are the Newton's Laws of Motion:

An object at rest will continue in its state of rest; while an object in uniform motion will continue in a straight line, unless an external force acts on it.

Newton's First Law of Motion.

Please read on Motion and Speed here.

The rate of change of momemtum is proportional to the applied force and will take place in the direction of that force.

Newton's Second Law of Motion.

To every action, there is an equal and opposite reaction.

Newton's Third Law of Motion.

Please read on Newton's Laws of Motion here.

The study of Thermodynamics revolves around the relationship between heat, temperature, energy and mechanical work; and these can be summarised under the 4 laws of Thermodynamics (Numbered zero through three).

You can read on the Concepts of Heat and Temperature here.

Below are the 4 laws of thermodynamics:

Zeroth law of thermodynamics – If two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other.

Please read on the Zeroth Law of Thermodynamics here.

1st law of thermodynamics – Energy can neither be created nor destroyed but can be changed from one form to another.

You can read on the Food Chain here.

2nd law of thermodynamics – The entropy of an isolated system not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium.

3rd law of thermodynamics – As temperature approaches absolute zero, the entropy of a system approaches a constant minimum.

Fuses are present in many electrical devices. They are basically 🔥 fire-breakers 🔥

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 or 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:

  1. The Laws of Motion (Classical Mechanics)
  2. Electromagnetism
  3. Relativity
  4. Thermodynamics

Please read on the basic introduction of the above physics concept here