Dynamics is branch of mechanics which deals with study of the behavior of bodies under the action of forces that produce motion in a body. There are several types of force in nature like muscular force, frictional force, magnetic force, gravitational force, electrical force etc. force responsible for the motion of bodies. The relation between force and motion was systematically introduced by Sir Isaac Newton in the form of three lows known as Newton’s lows of motion. Newton’s lows and other terms are discussed below:-

1) Newton’s first law: Every body continues in its state of rest or of its uniform motion in a straight line unless it is acted upon by an external force to change its state. This low explains the property of inertia and defines force.

2) Newton’s second law: The rate of change of momentum of a body is always directly proportional to the applied force and takes place in the direction of force. This defines unit of force and finds the magnitude of force (F= ma).

3) Newton’s Third low: For every action there is an equal and opposite reaction. This law explains that a force is always accompanied by an opposite and leads the law of conservation of momentum.

4) Inertia of rest: every body has tendency to be at rest and does not move unless compelled by a force. This property is called inertia of rest.

5) Inertia of motion: A body in motion has a tendency to move with uniform motion in a straight line, if there is no external acting on it. This property is called inertia of motion.

6) Velocity: Velocity is the rate of change of position of a body in a given time in a definite direction.

7) Weight; The force with which the earth attracts a body towards its center is called weight.

8) Mass: The quantity of matter contained in a body is called its mass.

9) Force: Force is that which changes or tends to change the state of rest or of its uniform motion in a straight line. In other words, force is push or pull that makes on object move or change shape or direction. Examples are gravity and magnetism.

10) Momentum: The impetus of a moving object is called momentum. It is equal to the mass of the object multiplied by its speed.


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