Secondary 4 Physics

The degree of hotness of an object, reflecting the average kinetic energy of the random motion of its particles; measured in degrees Celsius.

Energy transferred from a hotter object to a colder one because of a temperature difference, measured in joules.

The sum of the kinetic energy and potential energy of all the particles in a system.

The energy needed to raise the temperature of 1 kg of a substance by 1°C; for water it is 4200 J kg⁻¹ °C⁻¹.

The energy needed to raise the temperature of a whole object by 1°C; equal to mass times specific heat capacity.

The temperature unit with the ice point at 0 and the boiling point of water at 100 under standard atmospheric pressure.

The energy particles have due to their motion; the higher the temperature, the greater the average kinetic energy.

The energy particles have due to the forces between them; it changes when the state of matter changes.

The SI unit of energy (symbol J); heat is measured in joules.

An instrument that measures temperature using a property that changes with temperature, such as thermal expansion.

The transfer of heat through a solid by particle-to-particle passing of vibrational energy; metals also conduct quickly via free electrons.

The circulating flow set up when heated fluid rises and cooler fluid sinks, carrying heat through liquids and gases.

The transfer of energy by electromagnetic waves (mainly infra-red), which needs no medium at all.

The main component of thermal radiation; its wavelength is longer than visible light and it is invisible to the eye.

An electron in a metal that can move freely; free electrons make metals conduct heat and electricity especially well.

Mass per unit volume; heating makes fluid expand and become less dense, which drives convection.

A space with almost no matter; it blocks conduction and convection but radiation passes through.

The best emitter and absorber of radiation; shiny, light-coloured surfaces are the worst at both.

A container that cuts off conduction, convection and radiation at once with a vacuum jacket, silvered surfaces and a stopper.

The substance needed for a process; conduction and convection require a medium, radiation does not.

The form matter takes — solid, liquid or gas — each with its own particle arrangement and motion.

The temperature at which a solid melts; the freezing point equals it, e.g. 0°C for ice.

The temperature at which a liquid boils; water boils at 100°C under standard atmospheric pressure.

The interconversion between solid and liquid; melting absorbs energy, freezing releases it.

The interconversion between liquid and gas; vaporisation absorbs energy, condensation releases it.

The energy absorbed or released during a change of state while the temperature stays unchanged.

The energy needed to melt 1 kg of a solid completely; for water, 3.34 × 10⁵ J kg⁻¹.

The energy needed to vaporise 1 kg of a liquid completely; for water, 2.26 × 10⁶ J kg⁻¹.

Vaporisation below the boiling point, in which the most energetic particles escape from the surface; it has a cooling effect.

A graph of temperature against heating time; each plateau marks a change of state.

The location of an object relative to a chosen reference; a reference must be chosen before describing motion.

The total length of the path actually travelled; a scalar.

The change of position pointing straight from start to end, with magnitude and direction; a vector.

A quantity with magnitude only, such as distance, speed, time and mass.

A quantity with both magnitude and direction, such as displacement, velocity, acceleration and force.

Distance divided by time; magnitude only. Instantaneous speed is how fast at a particular moment.

Displacement divided by time, with magnitude and direction; average velocity is total displacement over total time.

The rate of change of velocity, in m s⁻²; 'accelerating' covers speeding up, slowing down and changing direction.

A graph of displacement against time; its slope gives the velocity.

A graph of velocity against time; its slope gives the acceleration and the area under it gives the displacement.

Straight-line motion with constant acceleration; its v-t graph is a sloping straight line.

The velocity at the start of the timed interval, symbol u.

The velocity at the end of the interval considered, symbol v.

The four relations v = u + at, s = ½(u + v)t, s = ut + ½at² and v² = u² + 2as.

Motion under gravity alone starting from rest, with acceleration g.

The acceleration of free fall, about 9.8 m s⁻² directed toward the ground.

The distance travelled from the moment braking starts to a complete stop.

The chosen positive direction for straight-line motion; quantities in the opposite direction take negative values.

Acceleration while slowing down; directed opposite to the motion and entered as a negative value.

The steady speed reached when air resistance balances weight during a fall.

A push or pull that changes an object's state of motion or its shape; a vector measured in newtons (N).

The vector sum of all forces acting on an object (the resultant).

The unit of force: 1 N gives a 1 kg mass an acceleration of 1 m s⁻².

An object's resistance to a change of its state of motion; the larger the mass, the greater the inertia.

With no net force, an object stays at rest or in uniform straight-line motion.

The acceleration of an object is proportional to the net force and inversely proportional to its mass: F = ma.

A simplified sketch of an object with arrows showing every force acting on it, used to find the net force.

The quantity of matter in an object and the measure of its inertia, in kilograms; unchanged by location.

The gravitational force on an object, W = mg, in newtons; varies with the local gravitational field.

The force opposing relative sliding or the tendency of sliding, directed against the motion (or tendency).