Introduction

Motion:

An object is in motion if its position changes with time.

Basic types of motion:

• Rectilinear or linear motion: Particle moves in a straight line.
• Circular or rotatory motion: Particle moves along a circle.
• Oscillatory or vibratory motion: Particle moves back and forth about a fixed point.

This unit deals with rectilinear motion or motion in a straight line.

Basic quantities:

The physical quantities can be either scalar quantities or vector quantities.

Info

Scalar quantities only have a magnitude. E.g.: time, distance, mass, etc.

Vector quantities have both magnitude and direction. E.g.: displacement, velocity, force, etc.

1. Distance:

• The total path length travelled by the particle.
• Scalar quantity.
• Unit: \(m\)

2. Displacement:

• Shortest distance between initial point and final point.
• Vector quantity.
• Unit: \(m\)

Distance vs. Displacement

Distance	Displacement
Actual path travelled by the object.	Shortest distance between initial and final points.
Scalar quantity.	Vector quantity.
Always positive.	Can be positive, negative or zero.
\(\geq\) displacement	\(\leq\) distance

3. Speed:

• Distance travelled per unit time. \((\text{Speed} = \frac{\text{Disance}}{\text{Time}})\)
• Scalar quantity.
• Unit: \(m/s\)

4. Velocity:

• Displacement of particle per unit time. \((\text{Velocity} = \frac{\text{Displacement}}{\text{Time}})\)
• Vector quantity.
• Unit: \(m/s\)

At a particular instant, instantaneous speed is equal to instantaneous velocity.

5. Acceleration:

• The rate of change of velocity per unit time.
• Vector quantity.
• Unit: \(m/s^2\)