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Matter and Energy.

posted Apr 8, 2018, 5:21 PM by Upali Salpadoru   [ updated Jun 22, 2021, 12:00 PM ]


Fig 1. A photograph of the sun taken by NASA during a total eclipse of the sun.               

What is matter?

Matter is generally described as the stuff that has mass and volume.

What is mass?

Referring to Newton’s second law, mass is a property of matter: It is reluctance to change the state of motion. This is also called INERTIA.

Quantity of Mass is measured in kilograms. In case of atoms, in ‘atomic mass units’. (amu).  ( The mass of Carbon-12 isotope is taken as 12amu.) Mass is a scalar quantity. Atomic mass of H is 1.674

1 dalton = 1 amu. 1 amu =1.674 x 10 x-27 kg.

What is energy?

A force is a quality that can produce an acceleration on a mass, unless there is an equal and opposite force, .  One newton, the unit of force can produce an acceleration of 1ms-1 , on a mass of 1 kg.

Force is a vector quantity.

Force = Mass x Acceleration.  

                 F = ma.

When a force acts on a mass, some work will be done or heat will be produced. Heat is due to motion of molecules; so this also can be considered as work

Work = Force x Displacement.

In units :-  Joules = newton x meters. J = nxm.

 Define energy.

This is generally described as the capacity to do work.

 1 Joule of work = 1 Joule of energy

Energy may be due to motion or position of matter, such as  

1. Kinetic energy due to motion of matter. This includes vibrations and rotations too. (Even sound and heat comes under this)

2. Potential energy is due to position of matter. (Gravitational p.e. and Elastic p.e.)

3. Chemical energy is due to entangling and disentangling of elctrons in matter. Accumulation, or deficiency  of electrons in matter (charges) or the flow of electrons or ions come under Electrical energy.

Other types of energy includes:-

4. Electromagnetic waves consist of packets of energy (quanta) that has the same velocity in space. (3x10 8 ms-1) eg. light, radio waves.

5. Nuclear energy is what holds the nucleons bound together inside the nuclei of atoms..

 Just a few decades ago, physicists were able to divide matter and energy into two distinct compartments. It is not that easy now. Let us find out why.

Let us now peep right inside the matter. Matter is made up of atoms. What are atoms? The structure and the model of the atom has a very long history.

Here is the story of the Atom in pictures:

 Democritus in 460 bc. “The smallest indivisible part of matter”
Plum pudding model.

John J Dalton. 1803

“ a number of negatively electrified corpuscles enclosed in a sphere of uniform positive electrification, .”

Rutherford model 1912

Positively charged nucleus with negatively charged electron orbiting at a distance.


Here are the important discoveries that throw some light into the structure of matter and the nature of energy,

John Dalton 1766-1844). UK, introduced the atomic theory.  The essence of it is even valid up to date.

In 1896 Henri Becquerel, discovered the strange rays coming from Uranium. Pierre Curie and Marie Curie discovered that the energy was not due to a hitherto known reaction and named the process as ‘Radioactivity

In 1897 John Thomson discovered a negatively charged particle, in cathode rays. He was even able to measure its charge . He called them corpuscles which we now know as ‘electrons

In 1904  JJ Thomson  introduced the plum pudding model of the atom.

1905 Albert Einstein introduced the Special theory of relativity. Matter and Energy was found to be two sides of the same coin.

Energy =  mass x Square of Velocity of light

J = kg x 300,000 km/s x 300,000 km/s

E = m c 

1905 Max Planck and Einstein showed that Light can behave as a particle as well as a wave.

1906  Rutherford discovered that the radioactive rays were a composition of three types. He named them as Alpha  α, Beta β and Gamma.

1907 Thomas Royds identified the alpha rays as a fast moving stream of Helium ions. He 2+.

1908 Professor Hans  Geiger and Samuel Marsden conducted the gold leaf experiment.

1909 Robert Millkan  (US), calculated the mass of the electron.

1913 Frederick soddy predicted the existence of isotopes.

1919 Arthur Eddington showed that light gets warped due to a massive mass such as the sun. As predicted by Einstein.

1920  Rutherford named the positive subatomic particle as a proton.

1924, Louis de Broglie suggested that, all microscopic material particles such as electrons, protons, atoms, molecules etc.can  behave as particles as well as waves.

Atomic mass of an atom and the mass of its components

Fig. Mass of Helium atom and the mass of its sub atomic components.

Let us work this out for the Helium atom.

Atomic mass of Helium= 4He2   

                 =4.0026 u

U stands for Atomic Mass Unit.

Mass of Components.

2 neutrons  = 2x 1.0087   …..= 2.0174

2 protons    = 2 x 1.007276…=2.01455

2 electrons = 2 x 0.0005    ..= 0,001.1

Total ………………………= 4.03305 u

Notice the difference.  …..How come?

Mass of an object must be equal to the mass of its parts. But here the Atom is lighter than the mass of its parts.  In the above case let us calculate the Mass defect.

                                  Mass defect = 4.03305 - 4.0026 ….=  0.03045

This should be the mass of energy known as the binding energy.

             4.0026 u + 0.03045 u (Energy)  = 4.03305 u

    Einstein’s General theory of relativity clearly states that matter gets converted to energy.

Using the equation  E = mc2 we can convert the mass of energy to Energy units.

The units should be    Joules = kilograms x velocity of light 2

First of all Mass defect should be converted to kilograms.