Myanmar Matriculation Physics key terms

The straight-line distance and direction from a starting point to a final point. It is a vector, so reversing direction changes its sign even when the path length travelled is unchanged.

The rate of change of displacement with time. It is a vector quantity measured in metres per second, and its direction matters as much as its magnitude.

The rate at which velocity changes with time. An object accelerates when it speeds up, slows down, or changes direction, and the unit is metres per second squared.

The resultant force on a body equals the product of its mass and acceleration, F = ma. The acceleration points in the same direction as the resultant force.

The single force that has the same effect as all the individual forces acting on a body combined. If it is zero, the body stays at rest or moves with constant velocity.

The state of a body when the forces on it balance, giving zero resultant force and zero resultant moment. The body is then at rest or moving steadily in a straight line.

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

The point through which the whole weight of a body appears to act, whatever its orientation. For a uniform regular shape it lies at the geometric centre.

How difficult it is to topple a body. It increases when the centre of gravity is low and the base is wide, because the weight line stays inside the base for larger tilts.

A scalar has magnitude only, such as mass, time, speed and energy. A vector has both magnitude and direction, such as displacement, velocity, force and acceleration, and vectors add by triangle or parallelogram rules.

The curved path of an object moving under gravity alone after being launched. Horizontal and vertical motions are treated separately: horizontal velocity stays constant while vertical velocity changes at g.

Motion in which gravity is the only force acting, so air resistance is ignored. All bodies then fall with the same acceleration g, about 9.8 metres per second squared near the Earth's surface.

The product of a force and the displacement in the direction of that force. It transfers energy, is measured in joules, and is zero when force and displacement are perpendicular.

The energy a body possesses because of its motion, equal to half the mass times the square of the speed. Doubling the speed quadruples the kinetic energy.

Energy cannot be created or destroyed, only transferred or transformed from one form to another. In a falling body, potential energy changes into kinetic energy plus heat from air resistance.

The rate at which work is done or energy is transferred, measured in watts. One watt equals one joule per second, and power can also be calculated as force times velocity.

The ratio of useful energy or power output to total energy or power input, usually expressed as a percentage. It is always less than 100 percent because some energy is lost, often as heat.

Force acting normally per unit area of a surface, measured in pascals. In a liquid, pressure increases with depth and depends on density and gravitational field strength.

The upward buoyant force on a body in a fluid equals the weight of fluid displaced. If this force equals the body's weight, the body floats.

Mass per unit volume of a substance, measured in kilograms per cubic metre. It is used with volume to find mass, and compared with fluid density to predict floating or sinking.

The energy needed to raise the temperature of one kilogram of a substance by one kelvin. Water's high value explains why it heats and cools slowly.

The energy absorbed or released when a substance changes state at constant temperature, without any temperature change. Specific latent heat is the energy per kilogram for that change.

The energy required to raise the temperature of a whole object by one kelvin, equal to mass times specific heat capacity. It is measured in joules per kelvin.

Changes of state from solid to liquid and liquid to gas. During each change, energy breaks bonds between particles, so temperature stays constant while latent heat is supplied.

A model describing a gas as many tiny particles in random motion, colliding elastically with each other and the container walls. Pressure arises from these collisions, and temperature measures average kinetic energy.

The equation pV = nRT relating pressure, volume, amount in moles, and absolute temperature of an ideal gas. It combines Boyle's, Charles's and pressure laws into one statement.

Temperature measured on the kelvin scale, starting at absolute zero where particle kinetic energy is minimum. Gas calculations must use kelvin, obtained by adding 273 to the Celsius value.

A disturbance that transfers energy from one place to another without transferring matter. Waves may be mechanical, needing a medium, or electromagnetic, travelling through a vacuum.

The distance between two consecutive points in phase on a wave, such as crest to crest. It is measured in metres and equals wave speed divided by frequency.

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

The distance travelled by a wave crest per second, given by speed equals frequency times wavelength. It depends on the medium, not on the amplitude.

The bending of a wave as it passes from one medium into another where its speed differs. The wave bends towards the normal when it slows down and away when it speeds up.

The ratio of the speed of light in a vacuum to its speed in a medium, always at least one. It also equals the sine of the angle of incidence divided by the sine of the angle of refraction.

The complete reflection of light inside a denser medium when the angle of incidence exceeds the critical angle. It requires travel towards a less dense medium and is used in optical fibres.

The spreading of waves after passing an obstacle or through a gap. It is most noticeable when the gap width is similar to the wavelength, which is why sound bends around corners more than light.

The superposition of two or more waves to give a combined wave. In phase, crests add to give reinforcement; out of phase, a crest and trough cancel to give cancellation.

Two wave sources that maintain a constant phase difference and have the same frequency. They are needed to produce a stable interference pattern of bright and dark fringes.

A large amplitude vibration produced when a driving frequency matches an object's natural frequency. It explains tuning circuits, musical instruments and the collapse of bridges in wind.

A wave pattern formed when two identical waves travel in opposite directions and superpose. It has nodes of zero displacement and antinodes of maximum displacement, and does not transfer energy.

The rate of flow of electric charge past a point, measured in amperes. One ampere equals one coulomb of charge passing per second, and conventional current flows from positive to negative.

The energy transferred per unit charge between two points in a circuit, measured in volts. One volt means one joule of energy is transferred per coulomb of charge.

The opposition of a component to current, equal to potential difference divided by current and measured in ohms. It depends on material, length, cross-sectional area and temperature.

The current through a conductor is directly proportional to the potential difference across it, provided temperature stays constant. Components obeying this have a straight-line current-voltage graph through the origin.

The production of an electromotive force in a conductor when magnetic flux through it changes. Moving a magnet into a coil, or rotating a coil in a field, induces a voltage.

The product of magnetic flux density and the area perpendicular to the field, measured in webers. A change in flux linkage with time induces an electromotive force in a coil.

The induced current flows in a direction that opposes the change producing it. This follows from conservation of energy and explains the opposing force felt when pushing a magnet into a coil.

The emission of electrons from a metal surface when light of sufficiently high frequency shines on it. It shows light behaves as particles called photons, each carrying energy proportional to frequency.

A discrete packet of electromagnetic energy, with energy equal to Planck's constant times frequency. Brighter light means more photons per second, not more energy per photon.

The minimum energy needed to remove an electron from the surface of a metal. It sets the threshold frequency below which no photoelectric emission occurs, however intense the light.

The time taken for half the nuclei in a radioactive sample to decay. It is constant for a given isotope and is used in carbon dating and medical tracer calculations.

The spontaneous emission of alpha particles, beta particles or gamma radiation from unstable nuclei. It is random and unaffected by temperature, pressure or chemical state.

The number of nuclear decays occurring per second in a sample, measured in becquerels. It falls exponentially with time and halves every half-life.

A circuit element that gives an output depending on its inputs, following rules such as AND, OR and NOT. Truth tables list every input combination and the resulting output.

A table showing the output of a logic gate or circuit for every possible combination of inputs. It is used to test and simplify logic circuits before they are built.

A p-n junction device that conducts easily in forward bias but hardly at all in reverse bias. It is used for rectification, converting alternating current into direct current.