Recall vector and scalar quantities, including: a displacement/distance b…

The idea

Learn each pair and decide which member needs a direction. Displacement is a vector (change in position with a stated direction) while distance is a scalar (how far travelled, no direction). Velocity is a vector (speed in a stated direction) while speed is a scalar. Acceleration is a vector because it has direction as well as magnitude. Force is a vector, and weight is a vector because it acts towards the centre of the Earth, whereas mass is a scalar measured in kilograms. Momentum is a vector, since it is mass multiplied by velocity and so inherits velocity's direction. Energy is a scalar: 200 J of thermal energy needs no direction. In multiple-choice items, match each option to the correct member of the pair and its classification.

What earns the marks

• Classifies displacement as a vector and distance as a scalar.
• Classifies velocity as a vector and speed as a scalar.
• Classifies acceleration as a vector.
• Classifies force and weight as vectors and mass as a scalar.
• Classifies momentum as a vector.
• Classifies energy as a scalar.

Common mistakes and how to put them right

• Treats distance as a vector because it is measured in metres.

  Put it right: Recognise that displacement, not distance, carries direction.

• Treats mass as a vector because it is measured in kilograms.

  Put it right: Recognise that weight, not mass, carries direction.

• Treats energy as a vector because it can be transferred.

  Put it right: Recognise that energy is a scalar with magnitude only.

• Treats momentum as a scalar because it is calculated from mass.

  Put it right: Recognise that multiplying by velocity gives it direction.

Exam tips

• Learn the list as pairs and name which member of each pair is the vector.
• Use the direction test on any unfamiliar option before choosing.
• Check that the option matches the exact quantity named in the question, not its partner in the pair.