Velocity, speed and acceleration

Velocity

Velocity, speed and acceleration are words that we often use to describe motion. We talk about high-speed trains, the acceleration of a sprinter or a Formula 1 racing car. In Physics these words have a precise meaning.

We use words like speed, constant speed, average speed and uniform acceleration to describe different types of motion.

The speed of an object does not require a direction to be considered, it simply has a value and unit, for example, 27 m\,s^{-1}.

Velocity is a vector quantity which requires a value, unit and direction, for example, 49 m\,s^{-1} to the left.

Speed-time graphs can be used to represent motions involving speed and uniform acceleration.

Velocity-time graphs can be used to represent the motion of objects travelling in a straight line, for example backward and forward, up and down, a positive and negative direction.