Zhongkao - independent subject foundations key terms

The straight-line distance and direction of a point from its starting position, treated as a vector quantity. It differs from distance travelled, which is a scalar and ignores direction.

The rate of change of displacement with respect to time, a vector quantity with both magnitude and direction. Average velocity divides total displacement by total time taken.

The rate at which velocity changes with time, including changes in speed, direction, or both. It is measured in metres per second squared and is a vector.

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, measured in newtons.

The product of a body's mass and its velocity, a vector measured in kilogram metre per second. For a chosen system, total momentum is conserved when the net external impulse is zero; closure to matter alone does not establish isolation from force.

The time integral of resultant force, or average resultant force times duration, equal to the change in momentum of the chosen body or system. It is measured in newton seconds and explains why airbags reduce injury.

The inward radial component of the resultant force for circular motion; in nonuniform motion a tangential resultant component can also be present. It has magnitude mv squared divided by radius r.

The rate of change of angular displacement, measured in radians per second. It links linear speed to circular motion through the relation speed equals radius times angular velocity.

The turning effect of a force about a pivot, equal to the force multiplied by the perpendicular distance from the pivot to its line of action. Measured in newton metres.

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

The single point through which the entire weight of a body may be considered to act, whatever its orientation. Its position affects stability and toppling.

The ratio of the speed of light in a vacuum to the speed of light in a medium, For light incident from vacuum or approximately air, it also equals sin(incidence)/sin(refraction); for two general media that ratio is their relative refractive index.

The angle of incidence in the denser medium for which the angle of refraction in the less dense medium is exactly ninety degrees. Beyond it total internal reflection occurs.

The complete reflection of light back into a denser medium when it strikes the boundary at an angle of incidence greater than the critical angle. It is used in optical fibres.

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

The superposition of two or more waves to produce regions of reinforced and cancelled displacement. Constructive interference gives maxima; destructive interference gives minima.

Two wave sources that maintain a constant phase difference and have the same frequency, so that a stable interference pattern can be observed. Lasers provide a common example.

A wave pattern formed when two waves of equal frequency and amplitude travel in opposite directions, producing fixed nodes and antinodes. Energy is not transported along the medium.

The large-amplitude oscillation that occurs when a system is driven at a frequency matching one of its natural frequencies. It is used in tuning circuits and musical instruments.

The charge stored per unit potential difference across a capacitor, measured in farads. For a parallel-plate capacitor it equals permittivity times area divided by plate separation.

For a capacitor-resistor circuit, the product of resistance and capacitance; it is the time for the charge to fall to about thirty-seven per cent of its initial value during discharge.

The force per unit positive charge experienced at a point in an electric field, measured in newtons per coulomb. It is a vector quantity with direction along the field line.

The energy transferred per unit charge when charge moves between two points in a circuit, measured in volts. It is the work done per coulomb.

The energy supplied by a source per unit charge driven around a complete circuit, measured in volts. It differs from terminal potential difference when internal resistance is present.

The resistance within a source of electromotive force that causes the terminal potential difference to fall as the current drawn increases. It dissipates energy as heat inside the source.

The generation of an electromotive force in a conductor when the magnetic flux linking it changes. The induced emf is proportional to the rate of change of flux linkage.

The product of the magnetic flux density and the area perpendicular to it, measured in webers. Flux linkage multiplies this by the number of turns in a coil.

The direction of an induced current is such that it opposes the change producing it. This is a consequence of conservation of energy and gives the negative sign in Faraday's law.

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

The energy absorbed or released when a substance changes state at constant temperature, without change in temperature. Specific latent heat is quoted per kilogram of substance.