Physics

Density and Specific Gravity

Alfred Ajibola - Tue, 10th September, 2019 @ 16:25: PM

Topics in Physics

Density and Specific Gravity Newton 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 Fundamental and Derived units Important 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

DENSITY:

Density has got a great deal to do with the mass/weight of substances. This is so because equal volumes of different substance have got different masses and weight; for instance; 10 gram of iron will be heavier (have a higher density) when compared to 10 gram of wood (which has a lower density). Similarly, 100ml of water will have a higher density than 100ml of oil; and for this reason, oil floats on water. Please read on Separation of mixtures (water and oil) here.

Note: What makes the difference in the density of different materials is as a result of the different atoms that make them up; for instance; water (H2O), which is made up of (Hydrogen and Oxygen in the ratio of 2:1) is different the constituents making up oil.

By Definition, Density is the mass of a unit volume of a material or substance.

You can read more on mass here.

Note: The principle of density was determined by a Greek scientist named Archimedes.

The formula for density is:
ρ = M/V
ρ = density
M = mass
V = volume
Note: Density can also be expressed by the Greek letters "rho"

The Standard International (SI) Unit for Density is Kilogram per Cubic Metre (Kg/m3). Below are some substances with their varying 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

 Sea Water (Saline/Salt Water)

 1030

 Blood. Please read on the Red Blood Cells here

 1600

 Glass

 2600

 Aluminium  (Al)

 2700

 Zinc (Zn)

 7100

 Iron (Fe)

 7900

 Copper (Cu)

 8900

 Lead (Pb)

 11300

 Mercury (Hg)

 13600

 Gold (Au). Please read interesting facts on Gold

 19300

 Platinum (Pt)

 21500

Notice from the table that helium has a lower density than air and that's one reason why it's used in filling balloons.

Having an understanding of density offers a convenient means of deriving the mass of a body from its volume. On the flip side, when we know the mass of a body, we can derive it's density.

Below are the derivation steps

Mass =  volume x density (M = Vd)

Volume = mass divided by the density (V = M/d).

Note: To get the weight of a body, we will need to multiply its mass by the acceleration of gravity.

Please read more on Gravity here.

A common application of density is seen in the way at which different materials interact with each other. For instance, a wood may float on water while an iron may sink in it. Also, balloons will float in air because it's filled with helium gas which is much lighter (has a lower density) than air.

 

Relative Density / Specific Gravity

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/relative density of less than 1 will float on water, while that with value greater than 1 will sink in water.

Below are the 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.

 

The table below shows the relative density of some substances:

 SUBSTANCE

 RELATIVE DENSITY

 Balsa Wood

 0.2

 Oak Wood

 0.75

 Ethanol (C2H5OH)

 0.78

 Liquid Paraffin

 0.8

 Olive Oil

 0.91

 Coconut Oil

 0.925

 Petroleum

 0.98

 Water (Fresh Water)

 1

 Salt Water (Reef Aquarium)

 1.025

 Ironwood

 1.5

 Graphite

 1.9 – 2.3

 Common  Salt (NaCl)

 2.17

 Aluminium (Al)

 2.7

 Cement

 3.15

 Iron  (Fe)

 7.87

 Copper (Cu)

 8.96

 Lead (Pb)

 11.35

 Gold (Au)

 19.3

 Osmium (Os)

 22.59


len

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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Amazing facts in Physics

Image Credit: Ball and Roller Store

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/s2Please read on gravity here


NOTABLE POINTS IN Physics

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/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

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