# Mechanics

## What is called Mechanics?

Mechanics is the study of rest and motion of physical bodies comparing with their surroundings and also dealt with different forces acting on them. Ir has two broad branches of studies –

1. Classical mechanics Classical mechanics is based on Isaac Newton’s laws of motion and has many sub-disciplines including kinematics, dynamics, statics, hydraulics and bio-mechanics.
2. Quantum mechanics – It deals with the mathematical description of the motion and interaction of subatomic particles like atoms and molecules etc., including the concepts of quantization of energy, dual nature of matter, the uncertainty principle, and the atomic structures and corresponding principles.

Therefore, the branch of physics which deals with the studies of conditions of rest or motion of material bodies is called mechanics.

### Branch of Classical Mechanics

Classical mechanics is divided into three sub-branches –

1. Statics.
2. Kinematics and
3. Kinetics or dynamics.

The basic differences between these branches of studies of mechanics are –

 STATICS KINEMATICS KINETICS OR DYNAMICS It is the branch of mechanics which deals with the study of objects at rest or in Here measurement of time is not essential. It is the branch of mechanics which only deals with the study of motion but not consider the factors which causes that motion such asor its multiples viz,andetc.Here measurement of time is essential. It is the branch of mechanics which deals with the study of motion of moving objects and the factors which causes that motion such as force, moment etc.Here measurement of time is essential.

### Difference between Kinetics & Kinematics

1. Statics is the branch of mechanics which only deals with the objects in rest.
2. Kinetics and Kinematics are the branches of mechanics which deals with the objects in motion.
3. Kinetics and kinematics, both terms though sound alike but there are various differences between them. Basic differences between them are tabulated below –
 Sl No KINETICS KINEMATICS 1 Kinetics deals with motion of objects along with cause of motion. Kinematics deals with motion of objects without considering the cause of motion. 2 Kinetics deals with forces and it’s multiples such as moment, couple, torque etc. Kinematics deals with properties of motion such as finding out velocities, accelerations, position of bodies etc. 3 It considers about mass of a body because force is related to mass. It doesn’t consider about mass of a body.

## State of Rest

If an object is not changing its position with time when compared with surrounding objects, then it is said to be in rest.

Example A book laying on top of a table is in rest.

## State of Motion

If an object is changing its position with pass of time when compared with surrounding objects, then it is said to be in motion.

Example – A train moving on rails is in motion.

### State of Rest and Motion are relative

“States of rest and motion of a body are relative”.

This statement can best understood with the help of examples.

1. Consider that a person is sitting on a moving bus. The person is said to be in the state of rest, if we consider and compare his position with reference to the position of other co passengers within the bus. But if we consider his position with reference to the position of fixed objects outside the bus, we can say that the person is in motion because his position is changing with time when compared with the position of objects outside the bus. Hence, a datum point for reference to express the state of rest or motion of a body is always essential.
2. Consider about a large mountain on the earth’s surface. The mountain is said to be in rest if compared with the position of other mountains or places on the earth’s surface. But, if we consider the position of that mountain comparing it with the position of sun or other planets in the universe, it seems to be in motion because earth is revolving round the sun and its position in always changing when compared with the position of other planets.

Therefore, it is concluded that the states of rest and motion of a body are always relative and expressed by comparing its position with the position of another body.

## Types of Motion

Motion of an object may be of three types –

1. One dimensional motion.
2. Two dimensional motion.
3. Three dimensional motion.

### 1. One Dimensional Motion

Out of three coordinates, if only one coordinate ( say x – coordinate ) is sufficient to specify the position of an object which is changing with time, then its motion is called one dimensional motion.

One dimensional motion is commonly known as Rectilinear motion or linear motion.

Examples – (1) Motion of a train in a straight track. (2) Motion of freely falling body.

### 2. Two Dimensional Motion

Out of three coordinates, if only two coordinates ( say x and y – coordinates ) are essential to specify the position of an object which are changing with time, then its motion is called two dimensional motion.

A two dimensional motion is commonly known as a planer motion.

Examples – (1) Motion of planets around the sun. (2) A car moving in a curved path.

### 3. Three Dimensional Motion

If all of three coordinates ( x, y and z coordinates ) become essential to specify the position of an object which are changing with time, then its motion is called three dimensional motion.

A three dimensional motion is commonly known as motion in space.

Examples – (1) A kite flying in sky. (2) Motion of an air plane.