Scalar and vector quantities
Scalars
Scalar quantities have only magnitude (size).
For example, 11 m and 15 m s-1 are both scalar quantities.
There are many scalar quantities:
- distanceNumerical description of how far apart two things are. For example, the distance from Edinburgh to Glasgow is approximately 50 miles.
- speedThe distance travelled in a fixed time period, usually one second.
- time
- power
- energy
Scalar quantities change when their magnitude changes.
Vectors
Vector quantities have both magnitude (size) and directionInformation to give the direction of travel, or the direction of a force, for example, a speed of 20 m s-1 to the left, or a force of 15 N to the right..
For example, 11 m east and 15 ms-1 at 30掳 to the horizontalParallel to the ground. are both vector quantities.
There are many vector quantities. This guide will use the following six:
- displacementQuantity describing the distance from the start of the journey to the end in a straight line with a described direction, eg 50 km due north of the original position.
- velocityThe speed of an object in a particular direction.
- accelerationThe rate of change in speed (or velocity) is measured in metres per second squared. Acceleration = change of velocity 梅 time taken.
- force
- weightThe force acting on an object due to the pull of gravity from a massive object like a planet. The force acts towards the centre of the planet and is measured in newtons (N).
- momentum
Vector quantities change when:
- their magnitude changes
- their direction changes
- their magnitude and direction both change
Example
A geostationaryA satellite orbiting a planet at the same rate as the planet. A geostationary satellite orbiting Earth has a period of 24 hours. satelliteBody that orbits a planet. For example, the Moon is a natural satellite of the Earth but communication satellites are artificial satellites of the Earth. is in orbit above the Earth. It moves at constant speed but its velocity is constantly changing (since its direction is always changing).
- the difference in two scalar quantities = large value - small value
- the difference in two vectors quantities = final vector - initial vector