NCEA Level 2 Physics key terms

A quantity that has both size and direction, such as force or velocity. Vectors are added tip-to-tail, and in two dimensions they are usually split into perpendicular components.

A quantity that has size only and no direction, such as mass, time, speed, energy or temperature. Scalars add arithmetically and are never written with an arrow.

The straight-line distance and direction from a starting point to a finishing point. Unlike distance travelled, it depends only on the two positions, not on the path taken.

The rate at which displacement changes, so it is speed in a stated direction. A car going round a bend at steady speed still changes velocity because its direction changes.

The rate at which velocity changes, measured in metres per second squared. It occurs whenever speed changes, direction changes, or both, and can be negative when an object slows down.

The single force that results from combining all forces acting on an object. It determines the object's acceleration through Newton's second law; zero net force means constant velocity.

The tendency of an object to keep doing what it is already doing, staying still or moving in a straight line at constant speed, unless a net force acts on it.

The force of gravity acting on an object, calculated as mass times gravitational field strength. Near Earth it is about 9.8 newtons per kilogram, and it changes on other planets.

The product of an object's mass and its velocity, measured in kilogram metres per second. It is a vector, so direction matters when adding or comparing momenta.

The change in momentum caused by a force acting for a period of time, equal to force multiplied by time. Airbags and crumple zones increase collision time to reduce the force.

The energy transferred when a force moves an object along its direction of action, calculated as force times distance moved. It is measured in joules.

Energy cannot be created or destroyed, only transferred between stores or transformed into other forms. The total energy in a closed system stays the same.

The net force, directed towards the centre of a circle, that keeps an object moving in a circular path. Without it the object travels in a straight line.

The rate at which electric charge flows past a point in a circuit, measured in amperes. One ampere is one coulomb of charge passing each second.

The energy transferred per unit charge as charge moves between two points in a circuit, measured in volts. Also called voltage; one volt is one joule per coulomb.

A measure of how much a component opposes current through it, calculated as voltage divided by current and measured in ohms. Longer, thinner or hotter wires have more resistance.

For a metallic conductor kept at constant temperature, current is directly proportional to the potential difference across it, so voltage equals current times resistance.

A circuit in which components are connected one after another, so the same current flows through each. The supply voltage is shared between them and total resistance adds up.

A circuit in which components are connected across the same two points, so each has the full supply voltage. The current splits between branches and total resistance is less than any branch.

The energy given to each unit of charge by a source such as a battery or generator, measured in volts. It differs from terminal voltage because some energy is lost overcoming internal resistance.

A region where a magnetic force can act on moving charges or magnetic materials. Field lines point from a magnet's north pole to its south pole and never cross.

The production of a voltage in a conductor when it experiences a changing magnetic field, for example when a magnet is moved in or out of a coil.

The distance between two matching points on consecutive waves, such as crest to crest. It is usually measured in metres and given the symbol lambda.

The number of complete waves passing a fixed point each second, measured in hertz. It is set by the source and does not change when a wave enters a new medium.

The time taken for one complete wave to pass a point, or for one full vibration to occur. It is the reciprocal of frequency and is measured in seconds.

The maximum distance a point on a wave moves from its rest position, measured in metres. Larger amplitude means the wave carries more energy.

The distance a wave travels each second, equal to frequency multiplied by wavelength. In a given medium it stays constant even when frequency or wavelength alone changes.

The change in direction of a wave as it crosses into a different medium where its speed changes. Light bends towards the normal when it slows down entering a denser medium.

The spreading of waves after they pass an edge or a gap. It is most noticeable when the gap is about the same size as, or smaller than, the wavelength.

The combining of two or more waves that meet at the same point. Crests meeting crests reinforce to give a larger wave, while a crest meeting a trough cancels out.

A wave pattern formed when two identical waves travel in opposite directions and superpose, producing fixed nodes and antinodes. It is created by reflection, for example in a vibrating string.

A helium nucleus made of two protons and two neutrons, emitted during some radioactive decays. It is relatively heavy, strongly ionising and stopped by a sheet of paper.

A fast electron emitted when a neutron in a nucleus turns into a proton. It is lighter and more penetrating than an alpha particle but less ionising.

A high-energy electromagnetic photon released when an excited nucleus loses energy. It has no mass or charge, is very penetrating and needs thick lead or concrete to stop it.

The time taken for half the atoms of a radioactive sample to decay, or for its activity to halve. Every half-life reduces the remaining activity by a further factor of two.

Atoms of the same element with the same number of protons but different numbers of neutrons. They share chemical properties but may have different mass numbers and stability.

The total number of protons and neutrons in the nucleus of an atom, written after the element's name or symbol. It is always a whole number.

The splitting of a heavy nucleus, such as uranium-235, into two lighter nuclei after absorbing a neutron. It releases a large amount of energy and further neutrons.

A packet of electromagnetic energy. The energy of one photon increases with the frequency of the radiation, which is why ultraviolet photons can damage living cells.