Scalar and Vector quantities

Scalar Quantity

A scalar quantity is a quantity which has magnitude (size) but no specific direction. It is completely described by a numerical value and an appropriate unit. Examples of scalar quantities are mass (e.g. 500 kg) and temperature (e.g. 100°C).

Scalar quantities change when the magnitude (size) changes.


Vector Quantity

A vector quantity is a quantity which has both magnitude (size) and a specific direction. Force is an example of a vector quantity because it is only completely defined by stating the size of the force and the direction in which it acts.

Vector quantities change when their:

  • Magnitude (size) changes
  • Direction changes
  • Magnitude (size) and direction changes.



magnitude (size) only
magnitude (size) and a specific direction
Distance is a measure of how far an object moves, e.g. 100 meters.
Displacement is the distance travelled in a particular direction from a specified point, e.g. 100 meters south east.
Speed is a measure of how fast an object is moving, e.g. 100 km/h
Velocity is the speed in a stated direction, e.g. 100 km/h south east.
Mass is a measure of the amount of matter in an object, e.g. 100 kg.
Weight is the force by which the earth attracts a body towards its centre, e.g. 10,000 Newtons.
Acceleration is the rate of change of velocity in a stated direction, e.g. 3 m/s2 to the left.
Force is a push or a pull in a particular direction, e.g. a frictional force of 10 N to the right tells us it is in the opposite direction to the motion of an object.
Momentum is the product of mass and velocity; and the direction of the momentum is stated by the direction given by the velocity.
Energy is the ability to do work. This only requires a numerical value with its unit to define it. For example, the electric kettle transferred 2000 Joules of energy.