Key definitions

AQA 8463 · 8463 mark-scheme terms

The quantities and laws AQA marks to the word — forces, energy, waves and radioactivity. A rough paraphrase loses the mark; learn the exact phrasing.

Reading mode — read across, know each one cold.

Term	Mark-scheme definition
Scalar quantity	A quantity that has magnitude (size) only.e.g. speed, distance, mass, energy, temperature.
Vector quantity	A quantity that has both magnitude and direction.e.g. velocity, displacement, force, acceleration, momentum.
Displacement	The distance travelled in a straight line in a particular direction (a vector).
Speed	The distance travelled per unit time (a scalar).
Velocity	The speed of an object in a given direction (a vector).
Acceleration	The change in velocity per unit time.
Mass	The amount of matter in an object (measured in kg).
Weight	The force acting on an object due to gravity (W = m g); measured in newtons.
Gravitational field strength (g)	The force per unit mass acting on an object (N/kg).
Resultant force	The single force that has the same effect as all the forces acting on an object added together.
Newton's First Law	If the resultant force on an object is zero, a stationary object stays still and a moving object keeps moving at a constant velocity.
Newton's Second Law	The acceleration of an object is proportional to the resultant force and inversely proportional to its mass (F = m a).
Newton's Third Law	When two objects interact, they exert equal and opposite forces on each other.
Work done	The energy transferred when a force moves an object through a distance (W = F s).1 joule of work is done when a force of 1 newton moves an object 1 metre.
Power	The rate of energy transfer, or the rate of doing work.1 watt = 1 joule per second.
Efficiency	(Useful output energy transfer / total input energy transfer) — multiply by 100 for a percentage.
Momentum	Mass x velocity (p = m v); a vector, measured in kg m/s.
Conservation of momentum	In a closed system, the total momentum before an event equals the total momentum after it.
Density	The mass per unit volume of a substance.density = mass / volume; unit kg/m³.
Hooke's Law	The extension of an elastic object is directly proportional to the force applied, provided the limit of proportionality is not exceeded.
Specific heat capacity	The energy needed to raise the temperature of 1 kg of a substance by 1 degree Celsius.
Specific latent heat	The energy needed to change the state of 1 kg of a substance with no change in temperature.
Wave	A disturbance that transfers energy from one place to another without transferring matter.
Transverse wave	A wave in which the oscillations are perpendicular to the direction of energy transfer.e.g. electromagnetic waves, ripples on water.
Longitudinal wave	A wave in which the oscillations are parallel to the direction of energy transfer.e.g. sound waves — shown as compressions and rarefactions.
Frequency	The number of waves passing a point per second (Hz).
Wavelength	The distance from one point on a wave to the equivalent point on the next wave.
Amplitude	The maximum displacement of a point on a wave from its undisturbed (rest) position.
Period	The time taken for one complete wave to pass a point (T = 1 / f).
Refraction	The change in direction of a wave as it changes speed when crossing a boundary between two media.
Radioactive decay	The random process by which an unstable nucleus emits radiation to become more stable.
Half-life	The time taken for the number of unstable nuclei in a sample (or the count rate) to halve.
Nuclear fission	The splitting of a large, unstable nucleus into two smaller nuclei, releasing energy and neutrons.
Nuclear fusion	The joining of two small nuclei to form a larger nucleus, releasing energy.
Renewable energy resource	A resource that is replenished as fast as it is used, so it will not run out.

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