Scalar quantity
Scalars & Vectors - OCR A-Level Physics
Key Definition
Scalar quantity
A quantity that has magnitude (size) only. It has no direction.
A quantity that has magnitude (size) only. It has no direction.
Key Definition
Vector quantity
A quantity that has both magnitude and direction.
A quantity that has both magnitude and direction.
- ScalarA quantity that has magnitude only, e.g. mass, speed, energy, temperature. examples: mass, temperature, speed, distance, energyThe capacity to do work. Measured in joules (J)., powerThe rate of energy transfer. Measured in watts (W)., time, pressureForce per unit area. Measured in pascals (Pa), where 1 Pa = 1 N m⁻²., chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C)., densityMass per unit volume of a material. Measured in kg m⁻³..
- VectorA quantity that has both magnitude and direction, e.g. velocity, force, displacement. examples: force, velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹., displacementThe distance moved in a particular direction from a starting point. A vector quantity. Measured in metres (m)., 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., momentum, weight, electric field strengthThe force per unit positive chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). at a point in an electric field. Measured in N C⁻¹ or V m⁻¹..
- Speed is scalar; velocityThe rate of change of displacementThe distance moved in a particular direction from a starting point. A vector quantity. Measured in metres (m).. A vector quantityA quantity that has both magnitude and direction.. Measured in m s⁻¹. is the vector equivalent (speed in a given direction).
- Distance is scalar; displacementThe distance moved in a particular direction from a starting point. A vector quantityA quantity that has both magnitude and direction.. Measured in metres (m). is the vector equivalent (distance in a given direction).
- Vectors are represented by arrows: the length shows magnitude, the arrowhead shows direction.
Common Mistake
MEDIUM
Wrong: Saying 'weight is a scalar because it is just a number in kg'.
Right: Weight is a VECTOR. It has magnitude (measured in newtons) AND direction (always towards the centre of the Earth). Mass is the scalar quantityA quantity that has magnitude (size) only. It has no direction. measured in kg.
Right: Weight is a VECTOR. It has magnitude (measured in newtons) AND direction (always towards the centre of the Earth). Mass is the scalar quantityA quantity that has magnitude (size) only. It has no direction. measured in kg.
Examiner Tips and Tricks
- A common 1-mark question asks you to classify a quantity as scalar or vector.
- The key test: does it have a direction?
- EnergyThe capacity to do work. Measured in joules (J)., powerThe rate of energy transfer. Measured in watts (W)., and temperature are the ones students most often get wrong -- all three are scalars.