# GCSE Additional Science - Physics - Motion - Velocity and acceleration.

Simple ways to remember velocity and acceleration.

## Velocity

Diferent ways of remembering what velocity is:

• Change in displacement over change in time.
• Speed in a given direction.
• A vector quantity which contains information about the speed of an object and its direction.
• Rate of change of displacement.

If the velocity of a body changes, we say it accelerates.

The SI unit of velocity is m/s.

remember that velocity must include a direction.

if a body changes direction, it changes velocity.

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## Acceleration

Acceleration is the rate of change of velocity as a function of time. It is vector. In calculus terms, acceleration is the second derivative of position with respect to time or, alternately, the first derivative of the velocity with respect to time.

Basically, Acceleration is change of velocity per second.

The SI unit of acceleration is m/s(squared)

we can calculate acceleration usuing the equation:

acceleration (m/s(squared)= change in velocity (m/s) /time taken for the change (s)

if the value calulated for acceleration is negative, it is decelerating - slowing down.

a body travelling at a steady speed is accelerating if its direction is changing.

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