What is Kinematics?

Kinematics is the study of motion of objects.
👉 It answers:

👉 It does NOT deal with the cause of motion (that is Dynamics → Forces)

Types of Motion

Type of Motion	Example
Rectilinear Motion (Straight line)	Train on track
Circular Motion	Fan blades, Earth around Sun
Oscillatory Motion	Pendulum, Guitar string
Rotational Motion	Wheel of car

It is defined as the distance travelled per unit time.
Distance (d)Path length covered Scalar quantity (only magnitude). Unit: metre (m).
Always positive or zero.

Relation: The magnitude of the displacement may or may not equal to the path of the path length traversed by an object.
|Displacement| ≤ |Distance| .

Example:A person walks 3 m East and then 4 m West.

Speed is a measure of how quickly an object moves from one place to another. It is defined as the distance travelled per unit time.
Formula: Speed = Distance / Time
SI Unit: metre per second (m/s), Other common units: kilometre per hour (km/h), miles per hour (mph)
Explanation:
- If a car travels 100 kilometres in 2 hours, its speed is 100km/2 hr = 50 km/h.
Speed is a scalar quantity, meaning it only has magnitude (how fast), not direction.
Rate of change of distance.
Scalar quantity.

Average Speed is the total distance travelled divided by the total time taken, regardless of any variations in speed during the journey.
Formula:Average Speed=Total Distance Travelled/Total Time Taken
SI Unit: metre per second (m/s). (also commonly expressed in kilometres per hour (km/h))
Key Points:
It does not depend on the direction — it is a scalar quantity.
It considers the entire journey, not just a particular moment.
If an object moves at different speeds during different time intervals, average speed gives one overall value.
Example:
- A car travels: 60 km in 2 hours, then 40 km in 1 hour.
  - Total Distance = 60 km + 40 km = 100 km
  - Total Time = 2 hours + 1 hour = 3 hours
  - Average Speed=100 km/3 hr≈33.33 km/h

Velocity is the rate of change of displacement of an object with respect to time. It tells us how fast and in which direction an object is moving.
Rate of change of displacement.
It may be positive or negative.
It is a Vector quantity.
Formula:
Velocity = Displacement / Time

An object is said to have uniform velocity if it covers equal displacements in equal intervals of time, in a fixed direction.
In other words, both speed and direction remain constant.
Example:
A car moving at 60 km/h towards the north without changing speed or direction.
Formula: v = Displacement/Time
Non-uniform Velocity:
An object has non-uniform velocity if it covers unequal displacements in equal intervals of time, or if its direction keeps changing.
This means speed, direction, or both change with time.
Example:
- A car moving through traffic, changing speeds.
- A car turning around a curve (direction is changing).

Relative velocity is the velocity of one object as observed from another moving object.
It tells you how fast one object appears to move with respect to another.
Formula:
If two objects are moving in the same straight line:
- V_relative= v₁– v₂
If both move in same direction, subtract the velocities.
If both move in opposite directions, add the velocities:
- V_relative= v₁+ v₂
Example:
- You are on a train moving at 80 km/h. Another train is moving at 100 km/h in the same direction.
- Relative velocity = 100 – 80 = 20 km/h.