Bookmark added to your notes.
View Notes

What is Mechanics?

Mechanics is a science that deals with the motion of objects under the effect of force. It also deals with the special case when the body stays at rest.

Here, our foremost concern is with the two bodies that exert forces on each other.

For example, the effect of gravity on the planets revolving around the sun, magnetic forces by which iron filings get attracted to the magnet and the electric force under which the two charges get attracted towards each other, and so on.


Mechanics is the area of physics that is concerned with the movement of physical objects. Forces applied to objects result in displacements, i.e., changes of an object's position relative to its surroundings.

Mechanics is divided into three following categories:

  • Statistical mechanics

  • Classical mechanics

  • Quantum mechanics

Statistical Mechanics

The word static in statistical means stable or at rest. So, statistical mechanics deals with the static objects on which the force is applied.

Statistical mechanics combines the principles of statistics to both classical and quantum Physics.

In today’s era, one of the fundamental concepts (pillars) of modern Physics is statistical mechanics. Statistical mechanics that treats and explains classical thermodynamics is statistical thermodynamics.

Let’s say, there are ‘N’ number of system of particles in thermal equilibrium at absolute temperature T, the energy E is associated with each particle, then the energy for ‘N’ particles will be:

N (E) = g (E) f (E)


N (E) = total energy of all the particles in a system.

g (E) = Number of state of energy (E) or the statistical weight regarding the energy

We call f (E) as the distribution function.

f (E) has two more meanings:

  • It is the average number of particles in each state of energy (E).

  • Probability/chance of occupancy of each state of energy (E).

Statistical mechanics help us determine how macroscopic properties, viz: temperature and pressure are related to microscopic properties that keep on varying on an average.

As we know that the classical thermodynamics can only measure and tabulate the quantities (heat capacity) of certain materials; however, statistical mechanics connects these thermodynamic quantities to microscopic behaviour.

Classical Mechanics

Classical mechanics deals with the objects in motion under the influence of a force or the equilibrium bodies whose all forces are balanced.

We can think of classical mechanics as the explanation of basic postulates of Isaac Newton mentioned in his book named Philosophiae Naturalis Principia Mathematica (1687), commonly known as the Principia.

We call these postulates Newton’s laws of motion. These laws help us forecast with great accuracy a wide variety of phenomena ranging from the motion of individual particles to the interactions of highly complicated systems.

The core concepts in classical mechanics are force, mass, and motion. Newton couldn’t define both mass and force. Since then these both have been the subject of much philosophical observation for Newton. However, both of these are best known for their effects.

Applying the first law of motion, we can say that mass is a measure of the tendency of a body to resist changes in its state of motion, while the force accelerates bodies, i.e., when it is applied to the body, it changes the state of motion of the body. The interconnection between these two effects is what we call classical mechanics.

What is Classical Mechanics in Physics?

Classical mechanics is a theory of Physics that takes into aspect the motion of macroscopic objects (objects visible with naked eyes), starting from projectiles to different parts of machinery, and astronomical objects, such as spacecraft, stars, planets, and galaxies.

For objects that are governed by classical mechanics, if the present state is known, we can predict how an object will move in the future (determinism) and how it has moved in the past (reversibility).

Quantum Mechanics

Quantum mechanics is the theory of science that studies with the behaviour of matter and light on the atomic and subatomic level.

Quantum mechanics is the fundamental tool that helps to understand at the theoretical stage and the electronic structure of chemical compounds and their mechanism, thermodynamics, chemical kinetics, and kinetics of chemical reactions.

Quantum mechanics attempts to describe and look for the properties of molecules and atoms and their constituents, viz: electrons, protons, neutrons, and many other esoteric particles such as quarks & gluons; these attributes involve the interactions of particles (at the microscopic level) with each other and with electromagnetic radiations such as light-rays, X-rays, and gamma-rays.

So, you understood how quantum physics explains how atoms work, and therefore, why chemistry and biology work as they do.

Point to Remember

Do you know mechanics and kinematics are related to each other? If you don’t know, let’s understand it.

The part of mechanics that describes motion without concerning its causes is called kinematics. It’s because kinematics does not take into account the cause of motion, it only considers the following parameters of motion; these are:

  • Speed

  • Displacement

  • Distance

  • Time

  • Velocity

FAQ (Frequently Asked Questions)

Question 1: List Seven Branches of Mechanics.

Answer: Seven branches of mechanics lie hereunder:

  • Thermodynamics.

  • Optics, light, lenses, colours.

  • Phenomena of vibrations and waves.

  • Relativistic mechanics.

  • Electromagnetism.

  • Quantum mechanics.

  • Mechanics of motion, objects, and interactions between them.

Question 2: How Many Types of Physicists are There?

Answer: The field generally involves the following two types of Physicists: Experimental physicists.

These types of Physicists are specialized in the observation of physical phenomena, and the analysis of experiments.

The second type of Physicists are theoretical physicists: They are specialized in mathematical modelling of physical systems to rationalize, explain, and predict natural phenomena.

Question 3: List the Hardest Branches of Physics.


  • Electromagnetism

  • Projectile Motion

  • String Theory

  • Electronics and communication

  • General Relativity theory

  • Relative Velocity

  • Radiation

  • Rotational mechanics

  • Quantum theory and mechanics

Question 4: Who is the Father of Classical Mechanics and in What Aspects it got Failed?

Answer: Galileo Galilei is the father of classical mechanics in addition to it, he is the father of scientific revolution and modern astronomy.

The failure of classical physics was to explain the blackbody radiation, the photoelectric effect, and the hydrogen atom. Because of the failure to explain these phenomena the concept of classical physics could not go further.