Scalar and Vector Quantities — AQA GCSE Physics
Physical quantities are either scalars (size only) or vectors (size and direction).
Scalars and vectors
- A scalar quantity has magnitude (size) only.
- A vector quantity has magnitude and direction.
Vectors are often represented by an arrow: the length shows the magnitude and the direction of the arrow shows the direction of the quantity.
Examples
| Scalars | Vectors |
|---|---|
| distance | displacement |
| speed | velocity |
| mass | force (including weight) |
| energy | acceleration |
| temperature | momentum |
Why the difference matters
Two quantities can have the same size but different directions, which makes them different vectors. For example, two forces of 10 N in opposite directions cancel out (resultant = 0), even though their magnitudes are equal.
Displacement is the straight-line distance and direction from start to finish, so a complete lap of a track gives a large distance but zero displacement.
Exam tips
- A scalar has size only; a vector has size and direction.
- Learn which common quantities are scalars and which are vectors.
- Vectors can be drawn as arrows (length = magnitude, direction = direction).
- Watch out for pairs like distance/displacement and speed/velocity.