EASA Module 2 Physics key terms

The mass of a substance per unit volume, usually measured in kilograms per cubic metre. It explains why equal volumes of different materials have different masses.

The internal force per unit cross-sectional area within a material, measured in pascals. External loads that stretch, compress or twist an object produce it.

The fractional change in a material's length or shape caused by an applied stress. It is a ratio of two lengths, so it has no units.

A measure of how stiff a solid is, found by dividing tensile stress by tensile strain while the material responds elastically. A higher value means less stretching under the same load.

The force acting perpendicular to a surface divided by the area of that surface, measured in pascals. It rises when the force increases or the area decreases.

In a confined fluid at rest, a change in pressure is transmitted equally in all directions and reaches every part of the fluid and its container.

An object immersed in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces. This principle explains floating and apparent loss of weight.

A physical quantity that is fully described by its magnitude alone, with no direction. Mass, time, temperature, speed and energy are examples.

A physical quantity that requires both magnitude and direction for a complete description. Force, velocity, displacement and acceleration are examples.

The straight-line distance and direction from an object's starting position to its current position. Unlike distance travelled, it is a vector and can be zero.

The rate of change of displacement with time, including its direction. It is a vector quantity measured in metres per second.

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

The resultant force acting on a body equals the body's mass multiplied by the acceleration it produces, with the force and acceleration in the same direction.

The product of a body's mass and its velocity, a vector quantity measured in kilogram metres per second. It indicates how difficult the body is to stop.

The product of a force and the time during which it acts, equal to the change in momentum produced. It is measured in newton seconds.

The energy transferred when a force moves an object through a distance in the direction of the force. It is measured in joules.

The rate at which work is done or energy is transferred, measured in watts. One watt equals one joule transferred each second.

The energy a body has because of its motion, equal to half its mass multiplied by the square of its speed, measured in joules.

The principle that energy cannot be created or destroyed, only transferred or converted between forms. The total energy of a closed system remains constant.

The turning effect of a force about a point, equal to the force multiplied by the perpendicular distance from the point to the force's line of action.

The state of a body when the vector sum of all forces on it is zero and the total turning moment about any point is also zero.

For a steadily flowing ideal fluid, an increase in flow speed is accompanied by a decrease in pressure, assuming no energy losses and no change in height.

A fluid's internal resistance to flow, caused by friction between its layers. Thick liquids such as honey have high viscosity and flow slowly.

A measure of the average kinetic energy of the particles in a body, showing how hot or cold it is and which way heat will flow.

Energy transferred between bodies because of a temperature difference. It moves from the hotter body to the colder one until both reach the same temperature.

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

The increase in a material's dimensions when its temperature rises, because its particles vibrate more and occupy more space. Different materials expand by different amounts.

The change in a system's internal energy equals the heat added to the system minus the work done by the system. It expresses energy conservation for thermal processes.

The relationship linking pressure, volume, absolute temperature and amount of an ideal gas: pressure times volume equals the number of moles times the gas constant times temperature.

The distance between two consecutive corresponding points on a wave, such as from one crest to the next, measured in metres.

The number of complete waves or oscillations passing a fixed point each second, measured in hertz. It equals one divided by the wave's period.

The maximum displacement of a particle from its rest position during a wave or oscillation. It indicates how much energy the wave carries.

The large increase in oscillation amplitude that occurs when a system is driven at its natural frequency. It can strengthen musical sounds or damage structures.

The apparent change in a wave's observed frequency caused by relative motion between the source and the observer. An approaching source is heard at a higher pitch.

The bending of a wave as it passes from one medium into another where its speed changes. It explains why objects appear bent when viewed through water.

The ratio of the speed of light in a vacuum to its speed in a given medium. A higher value means light travels more slowly and bends more.

The rule relating the angles of incidence and refraction to the refractive indices of two media: n1 sin θ1 equals n2 sin θ2.

The angle of incidence in a denser medium beyond which light is totally internally reflected instead of passing out into the less dense medium.

The complete reflection of light back into a denser medium when it strikes the boundary at an angle greater than the critical angle. Optical fibres use it to guide light.

The distance from the centre of a lens or mirror to its principal focus, where rays parallel to the axis converge or appear to diverge from.