This chapter deals with Classical physics. If you already have enough knowledge about Classical mechanics and its scope, you may skip this chapter. |

Classical Physics is the branch of physics that deals with the physics of macroscopic bodies. All the study of forces applied, energy released, motion, mechanical kinematics, laws of motion, thermodynamic design of bodies fall are under classical physics. Classical physics explains the cause of motion, most of the mechanical laws come under classical physics. Energy released by a body are discussed under classical thermodynamics. In fact, classical physics forms the base of all physical laws taught in schools and colleges.

However there are certain limits of classical physics. Classical physics can only explain the physics of body of size at least 10

^{-6}m. Classical physics is also limited to bodies moving at lower speeds (between 0 to 10,000 m/s). If the size of the body is below 10

^{-6}m or it is moving at a very high speed, many laws of classical physics break down and give rise to new laws called the particle physics laws. This would be discussed later.

**Classical Mechanics**

In physics, classical mechanics is one of the two major sub-fields of mechanics, which is concerned with the set of physical laws describing the motion of bodies under the action of a system of forces. The study of the motion of bodies is an ancient one, making classical mechanics one of the oldest and largest subjects in science, engineering and technology. Mechanics include Kinematics (Study of motion) and Dynamics (Study of the cause of motion).

Some terms related to classical mechanics are discussed below :

**Distance :**Total length of the path covered by a body.

**Displacement**: Length of the shortest line joining the initial point to final point is called Displacement.

**Scalars**: The physical quantities having only magnitude and no directions are called scalars. They follow algebraic rules.

**Vectors**: The physical quantities having magnitude as well as directions are called vectors. They follow vector rules.

**Speed**: In physics speed is defined as the rate at which a body covers distances. Its SI unit is m/s. It is a scalar quantity.

**Velocity**: In physics velocity is defined as the rate at which a body covers displacement (i.e a straight line drawn from initial to final position). Its SI unit it m/s. It is a vector quantity.

**Acceleration**: It is defined as a rate at which a body changes its velocity. It may be positive (when velocity increases) or negative (when rate of change of velocity decreases). Its SI unit is m/s

^{2}. It is a vector.

**Classical Equations for uniformly accelerated motion :**

If a body is uniformly accelerated then the following three equations are valid :

where

*v*is the final velocity of the body,

*u*is the initial velocity,

*a*is the constant acceleration and

*s*is the displacement of body.

**Inertia**: Inertia is caused due to mass. In fact Inertia is directly proportional to mass. Inertia is defined as the power of a body to resist motion. The more the mass the more the body would resist motion.

**Momentum**: It is opposite of Inertia. It is defined as the quantity of motion a body can do with its existing mass and velocity. In short it the product of mass and velocity. Its SI unit is Kg m/s.

where

*p*is momentum,*m*is mass and*v*is velocity.**Work :**It is defined as the product of force and displacement. The more the force or displacement the more is the work done by the body. Its SI unit is N-m or Joule (J).

where

*W*is Work done,*F*is Force applied and*s*is distance moved.**Energy**: In physics, energy is an indirectly observed quantity which comes in many forms, such as kinetic energy, potential energy, radiant energy, and many others.

where

*K.E*is Kinetic Energy,*m*is mass and*v*is velocity.

**Scope of classical physics**

The formulation of classical physics is quite accurate for heavenly bodies and holds equally good for grains and raindrops. However at molecular and sub atomic levels the laws of classical physics break up. The sub atomic and molecular bodies are governed by particle physics or quantum mechanics. Newton's law of motion also break when the velocity of a particle approaches speed of light. During the early 20th century there was an urgent need for new laws for high velocity motion. These new laws were formulated by Einstein in 1905 known as the relativistic mechanics. Quantum mechanics and Relativistic mechanics together give Quantum field Theory.

Most of the classical physics is mechanics. The causes of motion and gravity as explained by classical physics would be discussed in the later chapters. Classical thermodynamics and electrodynamics have very less or no relation with relativity so it has not been discussed here.

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