MATSEC AM Physics key terms

A measure of how strongly an object resists a change in its rotational motion, depending on its mass and on how that mass is spread about the axis of rotation.

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

A pair of equal, opposite and parallel forces whose lines of action do not coincide, producing rotation without any resultant translational force on the body.

The rotational analogue of linear momentum, equal to moment of inertia times angular velocity for a rigid body, and conserved when no external torque acts.

The rate of change of angular displacement with time, usually measured in radians per second, describing how fast a body spins about an axis.

The net force directed towards the centre of a circular path that keeps a body moving in that circle, with magnitude mv squared divided by radius.

The ratio of tensile stress to tensile strain for a material in the linear region of its stress-strain graph, a measure of stiffness independent of specimen dimensions.

The internal force per unit cross-sectional area within a deformed material, measured in pascals and used alongside strain to describe how a material responds to loading.

The fractional change in a dimension of a body caused by an applied force, a dimensionless quantity obtained by dividing the extension by the original length.

The greatest stress a material can bear and still return exactly to its original shape and size when the load is removed; beyond it permanent deformation occurs.

Irreversible change of shape of a material under stress, occurring beyond the elastic limit so that the body does not recover its original dimensions when unloaded.

The constant speed reached by a falling body when the upward drag force plus any upthrust exactly balances its weight, giving zero resultant force and zero acceleration.

For a body in equilibrium, the sum of clockwise moments about any point equals the sum of anticlockwise moments about that same point.

The force per unit positive charge experienced by a small test charge placed at a point in an electric field, a vector quantity measured in newtons per coulomb.

The work done per unit positive charge in bringing a small test charge from infinity to a point in an electric field; it is a scalar measured in volts.

The energy transferred per unit charge when charge moves between two points in a circuit, equal to the work done per coulomb passing between those points.

The energy supplied per unit charge by a source such as a battery or generator when converting other forms of energy into electrical energy; measured in volts.

The opposition to current flow inside a source of electromotive force, which causes the terminal potential difference to fall below the emf as current increases.

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 acting on a conductor placed at right angles to a magnetic field, measured in tesla.

The product of magnetic flux density and the area perpendicular to the field through a surface, measured in webers and used when applying electromagnetic induction laws.

The magnitude of an induced electromotive force in a circuit is directly proportional to the rate of change of magnetic flux linkage through that circuit.

The direction of an induced current is such that it produces a magnetic effect opposing the change that caused it, a consequence of conservation of energy.

The charge stored on one plate of a capacitor per unit potential difference across it, measured in farads; for a parallel-plate capacitor it depends on area and plate separation.

When two or more waves meet at a point, the resultant displacement equals the vector sum of the individual displacements; applied to light it explains interference patterns.

The reinforcement or cancellation that occurs when two coherent waves overlap, giving regions of greater and lesser intensity depending on their phase difference.

A property of two wave sources having a constant phase difference and the same frequency, a condition necessary for a stable observable interference pattern.

A wave pattern formed by two identical waves travelling in opposite directions, with fixed nodes and antinodes and no net transfer of energy.

The spreading of waves after passing through an aperture or around an obstacle, becoming more pronounced when the wavelength is comparable to the gap or obstacle size.

The restriction of transverse wave oscillations to a single plane, a property of light that demonstrates its transverse nature and is used in polarising filters.

A large amplitude response occurring when a system is driven at a frequency matching its natural frequency, with damping reducing the peak amplitude and broadening the response curve.

The angle of incidence in the denser medium for which the refracted ray travels along the boundary at ninety degrees, marking the onset of total internal reflection.

The ratio of the speed of light in a vacuum to its speed in a given medium, also equal to the ratio of the sines of the angles of incidence and refraction.

The complete reflection of light back into a denser medium when it strikes a boundary with a less dense medium at an angle greater than the critical angle.

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 needed 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, which changes when heat or work is transferred.

The emission of electrons from a metal surface when light of frequency above a threshold value falls on it, evidence for the particle nature of light.

The minimum energy required to remove an electron from the surface of a metal, related to the threshold frequency by the Planck equation.

A quantum of electromagnetic radiation carrying energy equal to Planck's constant multiplied by its frequency, with zero rest mass and momentum equal to energy divided by the speed of light.

The time taken for the number of undecayed nuclei in a radioactive sample, or its activity, to fall to half of its initial value.

The number of nuclear decays occurring per second in a radioactive sample, measured in becquerels and decreasing exponentially with time.

The energy required to separate all the nucleons in a nucleus completely, equivalent to the mass defect multiplied by the square of the speed of light.

The difference between the total mass of the separate nucleons and the mass of the assembled nucleus, appearing as the binding energy released during formation.

The range within which the true value of a measurement is expected to lie, often expressed as half the smallest scale division for a single reading.

The uncertainty in a measurement expressed as a fraction of the measured value multiplied by one hundred, used to judge the reliability of experimental results.