QCAA Physics key terms

A physical quantity that has both magnitude and direction, such as velocity or force, and which combines with others by geometric addition rather than simple arithmetic.

A physical quantity described fully by magnitude alone, without direction, such as mass, time, temperature or speed, so ordinary arithmetic applies to it.

The single vector that produces the same effect as two or more vectors added together, found by placing them head to tail or by summing components.

The part of a vector acting along a chosen axis, usually found using sine or cosine of an angle, so that perpendicular parts can be analysed separately.

A simplified drawing of an object as a point or box with labelled arrows showing every external force acting on it, used to apply Newton's laws.

The vector sum of all forces acting on an object; it determines the object's acceleration according to Newton's second law.

The relationship stating that an object's acceleration is directly proportional to the net force on it and inversely proportional to its mass, written as F = ma.

The tendency of an object to resist changes to its state of motion, measured by its mass; a more massive object is harder to accelerate.

The perpendicular contact force a surface exerts on an object resting or sliding on it, equal in size to the perpendicular component of weight only in simple cases.

A contact force opposing relative motion or the tendency to move between surfaces, arising from interactions between their microscopic irregularities.

The two-dimensional motion of an object moving under gravity alone after being launched, analysed by treating horizontal and vertical components independently.

Motion at constant speed along a circular path, requiring a centripetal force directed towards the centre that continuously changes the velocity's direction.

The acceleration of an object moving in a circle, directed towards the centre, with magnitude equal to speed squared divided by radius.

The product of an object's mass and velocity, a vector quantity that is conserved in any closed system where no external net force acts.

The product of a force and the time interval over which it acts, equal to the change in momentum produced and represented by the area under a force-time graph.

The principle that total momentum of an isolated system stays constant, so total momentum before an interaction equals total momentum after it.

The energy transferred to or from an object when a force acts on it through a displacement, calculated as the component of force along the displacement times that displacement.

The energy an object possesses because of its motion, equal to half its mass times the square of its speed, measured in joules.

The principle that energy cannot be created or destroyed, only transferred or transformed between forms, so the total in a closed system stays constant.

The gravitational force per unit mass experienced at a point in a gravitational field, equal to the local acceleration due to gravity.

The rule describing the electrostatic force between two point charges: proportional to the product of the charges and inversely proportional to the square of their separation.

The electrostatic force per unit positive charge at a point in an electric field, a vector quantity measured in newtons per coulomb.

The work done per unit positive charge in moving a charge from infinity to a point in an electric field, measured in volts.

A measure of the number of magnetic field lines passing through a given area, equal to the field strength times the perpendicular area.

The strength of a magnetic field expressed as flux per unit area perpendicular to the field, measured in tesla.

The generation of an electromotive force in a conductor whenever the magnetic flux through it changes, as described by Faraday's law.

The rule that an induced current flows in a direction whose magnetic effect opposes the change in flux that produced it, consistent with energy conservation.

The ability of a device to store charge per unit potential difference across it, measured in farads and given by charge divided by voltage.

The theory stating that the speed of light in a vacuum is the same for all inertial observers, so measured time intervals and lengths depend on relative motion.

The effect in which a clock moving relative to an observer ticks more slowly than one at rest with that observer, becoming pronounced near light speed.

The mass of a particle measured in a frame where the particle is stationary, an invariant quantity used in relativistic energy and momentum relationships.

A discrete packet of electromagnetic energy whose energy equals Planck's constant multiplied by frequency, exhibiting both wave and particle behaviour.

The emission of electrons from a metal surface when light of sufficiently high frequency strikes it, explained by photons transferring energy to individual electrons.

The minimum energy required to remove an electron from the surface of a particular metal, characteristic of that material.

The lowest frequency of incident light that can cause photoelectric emission from a given metal, corresponding to photon energy equal to the work function.

The range within which a measured value is expected to lie, arising from limitations of instruments and technique and reported alongside the measurement.

The uncertainty of a measurement expressed in the same units as the measurement itself, often taken as half the smallest scale division of an analogue instrument.

The absolute uncertainty divided by the measured value, multiplied by one hundred, allowing comparison of precision between measurements of different sizes.

The extent to which repeated measurements under the same conditions give consistent results, improved by taking multiple trials and averaging them.

The extent to which an investigation actually measures the quantity it claims to measure, requiring suitable equipment and control of relevant variables.

A factor deliberately kept constant throughout an experiment so that it cannot influence the dependent variable and confound the results.

The variable deliberately changed by the experimenter between trials, whose effect on the dependent variable is being investigated.

Unpredictable variation in measurements about a true value, caused by factors such as reaction time or fluctuations, reduced by averaging repeated trials.

A consistent offset in measurements in one direction, caused by faulty calibration or zero error, which averaging repeated trials cannot remove.

A focused, answerable question that guides a scientific investigation, specifying the variables or phenomenon to be examined and the context.

A statement asserting that something is true about a scientific phenomenon, which an investigation evaluates using gathered evidence and reasoning.

Information collected by someone other than the investigator, such as published measurements or databases, used when primary collection is impractical.