VCE Physics key terms

A quantity that has both magnitude and direction, such as displacement, velocity, acceleration or force. Vectors add by head-to-tail geometry or by resolving into perpendicular components.

A quantity described fully by magnitude alone, with no direction. Distance, speed, mass, time, energy and temperature are scalars.

The straight-line change in position from start to finish, including direction. It depends only on the endpoints, not on the path taken.

The total length of the path actually travelled, regardless of direction. It is a scalar and is always at least as large as the magnitude of displacement.

The rate at which distance is covered, found by dividing distance travelled by time taken. It is a scalar and ignores direction of travel.

The rate of change of displacement, found by dividing displacement by time. It is a vector, so a change of direction is a change of velocity even at constant speed.

The rate of change of velocity, found by dividing the change in velocity by the time taken. Because velocity is a vector, acceleration can arise from changing speed or changing direction.

The single vector that has the same effect as two or more vectors combined. It is found by vector addition, for example by completing a triangle or parallelogram.

Splitting a single vector into two perpendicular components, usually horizontal and vertical, using trigonometry. It simplifies problems where motion or forces act in independent directions.

The vector sum of all forces acting on an object. It determines the object's acceleration, not its velocity, so a zero net force means constant velocity.

An object stays at rest or moves with constant velocity unless acted on by a net external force. It defines inertia and explains why seatbelts and friction matter.

The tendency of an object to resist changes in its motion. It depends only on mass, so a more massive object needs a larger net force for the same acceleration.

The net force on an object equals its mass multiplied by its acceleration, written as F = ma. The acceleration is always in the direction of the net force.

For every action force there is an equal and opposite reaction force, acting on a different object. The pair never cancels because the two forces act on separate bodies.

The gravitational force on an object, equal to its mass multiplied by gravitational field strength. It is a force measured in newtons and changes with location.

A measure of the amount of matter in an object and of its inertia. It is a scalar measured in kilograms and does not change with gravitational field strength.

The support force a surface exerts perpendicular to itself on an object touching it. On a flat surface it equals weight only when no other vertical forces act.

A contact force that opposes relative sliding or attempted sliding between surfaces. Kinetic friction acts during sliding; static friction adjusts up to a maximum value.

A sloping surface that changes the direction of the normal force and introduces a component of weight along the slope. This component causes acceleration down the incline.

The product of an object's mass and velocity, a vector measured in kilogram metres per second. Momentum is conserved in collisions when no external net force acts.

The product of a force and the time for which it acts, equal to the change in momentum. Extending the contact time reduces the peak force in impacts.

In an isolated system with no net external force, the total momentum before an interaction equals the total momentum after it. It applies to collisions and explosions.

A collision in which both momentum and total kinetic energy are conserved. Objects bounce apart with no permanent deformation and no energy lost to heat or sound.

A collision in which momentum is conserved but total kinetic energy is not, because some energy converts to heat, sound or deformation. Objects may stick together.

The energy an object has because of its motion, equal to half its mass times its speed squared. It is a scalar measured in joules and is always non-negative.

Energy stored in an object because of its position in a gravitational field, near Earth equal to mass times field strength times height. It converts to kinetic energy as an object falls.

The energy transferred when a force moves an object along its line of action, equal to force times displacement in that direction. It is measured in joules.

Energy cannot be created or destroyed, only transformed or transferred between objects and stores. The total energy of an isolated system stays constant.

The rate at which energy is transferred or work is done, equal to energy divided by time. It is measured in watts, where one watt is one joule per second.

The ratio of useful energy output to total energy input, often expressed as a percentage. It is always less than one hundred percent because some energy is dissipated.

Motion along a circular path at constant or varying speed. Even at constant speed the direction of velocity changes continuously, so the object accelerates towards the centre.

The net force directed toward the centre of a circular path that keeps an object moving in that circle. It is provided by tension, gravity, friction or a normal force.

The time taken for one complete cycle of a repeating motion, such as one full orbit or one rotation. It is measured in seconds and is the reciprocal of frequency.

The gravitational force per unit mass at a point, equal to the local acceleration due to gravity. Near Earth's surface it is about 9.8 newtons per kilogram.

The curved path of an object around a more massive body, held by gravity. For a circular orbit, gravitational force supplies the required centripetal force.

The generation of an electromotive force in a conductor when the magnetic flux through it changes. Changing flux can come from motion, rotation or a varying current.

A measure of the number of magnetic field lines passing through a given area, equal to field strength times area times the cosine of the angle between them. It is measured in webers.

The induced electromotive force equals the negative rate of change of magnetic flux through a circuit. Faster flux change or more turns gives a larger induced voltage.

An induced current flows in the direction that opposes the change in flux that produced it. This follows from conservation of energy and explains the negative sign in Faraday's law.