3.4.1.1
A scalar has magnitude only; a vector has magnitude and direction
Scalars & Vectors — AQA A-Level Physics
Key Definition
Scalar — A quantity that has magnitude (size) only.
Key Definition
Vector — A quantity that has both magnitude and direction.
- Distance is scalar; displacementThe distance moved in a particular direction from a starting point. A vector quantity. Measured in metres (m). is vector. Distance tells you how far an object has travelled overall. DisplacementThe distance moved in a particular direction from a starting point. A vector quantity. Measured in metres (m). tells you how far it is from its starting point and in what direction.
- Speed is scalar; velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹. is vector.
- Mass, time, energyThe capacity to do work. Measured in joules (J)., volume, densityMass per unit volume of a material. Measured in kg m⁻³., pressureForce per unit area. Measured in pascals (Pa), where 1 Pa = 1 N m⁻²., electric chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). and temperature are all scalars.
- DisplacementThe distance moved in a particular direction from a starting point. A vector quantity. Measured in metres (m)., velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹., accelerationThe rate of change of velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹.. A vector quantity. Measured in m s⁻²., force and momentum are all vectors.
Examiner Tips and Tricks
- Quick test: can the quantity have a minus sign with physical meaning?
- Negative displacement makes sense (opposite direction).
- Negative energyThe capacity to do work. Measured in joules (J). does not.
- If a minus sign is meaningful, it is a vector.
Related:Kinematics