# Basic Knowledge of Acceleration

Physics

## definition

### Acceleration

Acceleration is defined as the rate of change of velocity with time. It is a vector quantity. Its unit is
Constant speed does not guarantee that acceleration is zero. For example a body moving with constant speed in a circle changes its velocity every instant and hence its acceleration is not equal to zero.

## definition

### Retardation

Retardation (or deceleration) of a body whose velocity is decreasing with time is defined as the negative of acceleration. In other words, it is equal to the magnitude of acceleration of a body whose velocity is decreasing with time.
For a decelerating body, direction of velocity and acceleration is always opposite in direction.
Example: When a body is thrown vertically upwards, during the upward motion, its velocity decreases and at the highest point it becomes zero. This is a case of retardation.

## definition

### Unit of Acceleration

Acceleration is defined as the rate of change of velocity or velocity per unit time.Its unit is , can also be expressed as .
Centripetal acceleration:Centripetal acceleration is the rate of change of tangential velocity.