STRAIGHT LINE MOTION: Dynamics, Newton's Laws of motion, Newton's First Law of motion, Newton's Second Law of motion and Newton's Third Law of motion ~ MECHTECH GURU

# STRAIGHT LINE MOTION

## Dynamics

Dynamics is a branch of mechanics which deals with the motion of the bodies under the action of forces.

A body is said to be at rest if it does not change its place or position with respect to its surroundings.

No body in this earth is at absolute rest. Because, they are sharing the motion of the earth. A body can be at rest with respect to another body.

A body is said to be in motion if it changes its place or position with respect to its surroundings. For example, a person in the moving train feels the motion, seeing the passing objects through the windows.

Hence rest and motion are relative terms.

The motion of the body is characterised by two quantities, Force and Momentum.

If a body is in motion with acceleration, then the body is acted upon by a force (F=ma). If a body is in motion with uniform velocity, there is no acceleration, then the motion of the body is only under momentum (mv).

## Newton's Laws of motion

Newton's Laws of motion: These laws are very important in dynamics.

### Newton's  First Law of motion

Every body continues to be in its state of rest or of uniform motion in a straight line unless compelled by an external force.

### Newton's Second Law of motion

The rate of change of momentum of a body is directly proportional to the force acting on it and it takes place in the direction of the force.

### Newton's  Third Law of motion

For every action, there is always an equal and opposite reaction.

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