# Distance, Displacement, Speed, Velocity and Acceleration

This post is about the definition, units and dimensions of distance, displacement, speed, velocity, Acceleration, the difference between distance and displacement, and the difference between speed and velocity.

## Distance-

Distance is the length of the actual path covered by a moving object in a given time interval.

### Units of Distance-

• SI unit of distance is metre (m)
• CGS unit of distance is centimetre (cm)

But in our daily life, we come across the bigger units of distance e.g. kilometer.

### Characteristics of distance :

1. Distance is a scalar quantity.
2. Distance travelled by a body in a given interval of time is always positive.
3. Distance travelled by vehicles is measured by a device ODOMETER, fitted on the dash board of vehicles.
4. It can never be zero or negative.

## Displacement-

It is the shortest distance travelled by the object between the initial to final positions of the object.

### Units of Displacement-

• SI unit of displacement is metre (m)
• CGS unit of displacement is a centimetre (cm)

The dimensional formula for displacement is [M0LT0]

`Displacement of an object in motion can be positive, negative or zero.`

### Characteristics of displacement-

1. Displacement has the unit of length.
2. Displacement of any object in a given interval of time may be positive, negative or zero.
3. Displacement of any object is a vector quantity as it has both magnitude and direction.
4. Displacement of any object is the shortest path between two positions.

## Speed

The speed of any object in motion is the ratio of the total path length (distance) and corresponding time taken by the object i.e,

Speed = Total distance / Time taken

Speed is a scalar quantity as it has only magnitude but no direction.

`Speed of object gives no idea about the direction of motion of object. It may be positive and zero but never negative.`

### Unit of Speed-

In the SI system, the unit of speed is m/s and in the CGS system of the unit of speed is cm/s.

Speed of vehicles like car, bus etc. is expressed in km/h

Dimension formula of speed [M0LT-1]

## Velocity

The rate of change of displacement with respect to time is called velocity.

Velocity = Displacement / Time

### Unit of Velocity

SI unit of velocity is m/s and CGS unit of velocity is cm/s

It is also expressed in km/h.

Dimension formula of Velocity [M0LT-1]

### Characteristics of Velocity–

• As velocity has both magnitude and direction so, it is a vector quantity.
• The velocity of an object can be positive, negative or zero according to displacement which can be positive, negative or zero.

## Acceleration

Acceleration is defined as the rate of change of velocity with respect to time. Also defined as the change in velocity of object in unit time.

Acceleration = Change in velocity / Time

Acceleration is a vector quantity. Its direction is same as that of change in velocity.

SI unit of acceleration = m/s2

CGS unit of acceleration = cm/s2

Dimensional formula of acceleration = [M°LT-2]

Acceleration of the object is positive if the velocity is increasing and is negative if the velocity is decreasing.

The negative acceleration is also called as Retardation or Deceleration.

## FAQs

### What is Distance?

Distance is the length of the actual path covered by a moving object in a given time interval.