NSSCAS Physics (8225) key terms

The straight-line distance and direction from an object's starting point to its current position; a vector quantity measured in metres, distinct from the total path length travelled.

The rate of change of displacement with respect to time, including direction; measured in metres per second and equal to the gradient of a displacement-time graph.

The rate at which velocity changes with time, including any change of direction; measured in metres per second squared and given by the gradient of a velocity-time graph.

Motion under gravity alone, with air resistance negligible, so that every object near a given point accelerates downwards at the same rate regardless of its mass.

Scalars have magnitude only, such as mass, speed and energy; vectors have magnitude and direction, such as force, velocity and momentum, and are added by resolving into components.

Two-dimensional motion of an object moving freely under gravity, analysed by treating horizontal and vertical components independently: constant horizontal velocity and uniform vertical acceleration.

The single force that produces the same effect as all the forces acting on a body combined; found by vector addition of the individual forces.

The state of a body when the net force and net moment acting on it are both zero, so it remains at rest or continues moving with constant velocity.

The turning effect of a force about a pivot, calculated as force multiplied by the perpendicular distance from the pivot to the line of action of the force.

The point through which the entire weight of a body may be considered to act, so that a force applied there produces no turning effect due to weight.

A body remains at rest or moves with constant velocity unless acted on by a resultant force; a statement of inertia and of the condition for equilibrium.

The tendency of an object to resist changes to its state of motion, determined solely by its mass; a larger mass means a smaller acceleration for the same resultant force.

The resultant force on a body equals the rate of change of its momentum; for constant mass this reduces to force equals mass times acceleration.

The product of an object's mass and velocity, a vector quantity measured in kilogram metres per second, representing the quantity of motion it possesses.

The product of a force and the time for which it acts, equal to the change in momentum produced; the area under a force-time graph.

In a closed system with no external resultant force, the total momentum before an interaction equals the total momentum afterwards, applying to collisions and explosions.

A collision in which both momentum and total kinetic energy are conserved, so the objects separate with no loss of kinetic energy to other forms.

A collision in which momentum is conserved but total kinetic energy is not, some energy being transferred to internal energy, sound or deformation.

The energy transferred when a force moves an object through a distance in the direction of the force; calculated as force times displacement along the force.

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

Energy cannot be created or destroyed, only transferred between stores or transformed from one form to another; the total energy of a closed system remains constant.

The rate at which energy is transferred or work is done, measured in watts; equal to work done divided by time taken, or force multiplied by velocity.

The ratio of useful energy or power output to total energy or power input, usually expressed as a percentage; the remainder is dissipated, often as internal energy.

The force applied per unit cross-sectional area of a material, measured in pascals; a measure of the internal loading that produces strain.

The fractional change in length of an object, equal to extension divided by original length; a dimensionless ratio describing deformation.

The ratio of tensile stress to tensile strain for a material in the linear region of its force-extension graph; a measure of stiffness, measured in pascals.

The maximum stress a material can withstand and still return to its original shape when the load is removed; beyond it, permanent deformation occurs.

The extension of a spring or wire is directly proportional to the applied force, provided the elastic limit is not exceeded; the constant of proportionality is the spring constant.

A wave in which the oscillations are perpendicular to the direction of energy transfer, such as light or waves on a string; it can be polarised.

A wave in which the oscillations are parallel to the direction of energy transfer, such as sound; it consists of compressions and rarefactions and cannot be polarised.

The spreading of waves as they pass through an aperture or around an obstacle; most pronounced when the wavelength is comparable to the size of the gap.

When two or more waves meet at a point, the resultant displacement equals the vector sum of the individual displacements, producing reinforcement or cancellation.

The superposition of waves from coherent sources, producing a pattern of constructive reinforcement where waves arrive in phase and destructive cancellation where they arrive in antiphase.

A property of two wave sources that maintain a constant phase difference and the same frequency, a requirement for a stable observable interference pattern.

The restriction of oscillations of a transverse wave to a single plane; evidence that light is transverse, and achievable using a polarising filter.

The change in direction of a wave as it passes from one medium to another due to a change in speed, described by Snell's law relating angles and refractive indices.

The complete reflection of a wave at a boundary when travelling from a denser to a less dense medium at an angle of incidence greater than the critical angle.

The rate of flow of electric charge past a point in a circuit, measured in amperes; one ampere is one coulomb of charge passing per second.

The energy transferred from electrical to other forms per unit charge passing between two points in a circuit; measured in volts, equal to one joule per coulomb.

The energy supplied by a source per unit charge driven around a complete circuit, measured in volts; it equals the potential difference across the source when no current flows.

The opposition to current flow in a component, defined as potential difference across it divided by current through it and measured in ohms.

The resistance within a source of electromotive force that causes its terminal potential difference to fall as the current drawn from it increases.

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

The work done per unit positive charge in bringing a small test charge from infinity to a point in an electric field; measured in volts and zero at infinity.

The electrostatic force between two point charges is proportional to the product of the charges and inversely proportional to the square of the distance between them.

The magnetic force per unit current per unit length on a conductor placed at right angles to a magnetic field; a vector measured in teslas.

The product of magnetic flux density and the area through which it passes perpendicularly, measured in webers; it quantifies the field threading a surface.

The generation of an electromotive force in a conductor whenever the magnetic flux linking it changes, forming the basis of generators and transformers.

The induced electromotive force is directly proportional to the rate of change of magnetic flux linkage through a circuit; a faster change gives a larger induced emf.

The direction of an induced current is such that it opposes the change in magnetic flux that produced it, a consequence of energy conservation.

The energy required to raise the temperature of one kilogram of a substance by one kelvin, measured in joules per kilogram per kelvin.

The energy required to change the state of one kilogram of a substance at constant temperature, without any change in temperature during the process.

The sum of the randomly distributed kinetic and potential energies of all the particles within a system; it increases when temperature rises or state changes.

A model gas whose particles occupy negligible volume and exert no forces except during elastic collisions; its pressure, volume and temperature obey the gas equation.

The lowest possible temperature, zero kelvin, at which particles have minimum kinetic energy; equivalent to minus 273 degrees Celsius.

The degree of repeatability of a measurement, reflected in how closely repeated readings agree with each other; a precise instrument gives a small spread of values.

How close a measured value is to the true value; a systematic error reduces accuracy, whereas random errors mainly reduce precision.

The range within which the true value of a measurement is likely to lie, often expressed as plus or minus half the smallest scale division or from repeated readings.

A consistent error affecting all readings in the same direction, caused by faulty apparatus or flawed method; it reduces accuracy and is not removed by averaging.