BGCSE Physics (0571) key terms

A quantity that is fully described by a size alone, with no direction needed. Mass, time, temperature and speed are examples, unlike vectors such as force.

A quantity that needs both a size and a direction to describe it completely. Force, velocity, acceleration and weight are examples, and they add by drawing arrows tip to tail.

The single force that has the same effect as all the forces acting on an object combined. If it is zero the object keeps a steady speed or stays still.

The resultant force on an object equals its mass multiplied by its acceleration. A larger force gives a larger acceleration, and a heavier object accelerates less for the same force.

The rate at which velocity changes, measured in metres per second squared. It can mean speeding up, slowing down or changing direction, and it is caused by a resultant force.

Speed in a stated direction, measured in metres per second. An object moving round a curve at steady speed still changes velocity because its direction keeps changing.

The distance travelled by an object in each unit of time, measured in metres per second. It is a scalar, so direction is not included in the value.

A graph plotting distance travelled against time. The slope of the line gives the speed, so a flat line means the object is stationary and a steeper line means faster motion.

The turning effect of a force about a pivot, calculated as force multiplied by the perpendicular distance from the pivot. It is measured in newton metres.

For an object in equilibrium, the total clockwise moment about a pivot equals the total anticlockwise moment about the same pivot. This lets unknown forces or distances be calculated.

The point at which the whole weight of an object appears to act. If the vertical line through it falls outside the base, the object topples over.

The force of gravity acting on an object, measured in newtons. It equals mass multiplied by gravitational field strength, so it changes on different planets while mass does not.

The amount of matter in an object, measured in kilograms. It stays the same wherever the object is and measures how hard the object is to accelerate.

The energy an object has because it is moving, equal to half its mass multiplied by the square of its speed. Doubling the speed gives four times the kinetic energy.

Energy stored in an object because of its position or shape, for example a raised mass or a stretched spring. It is measured in joules and can be transferred to other forms.

Energy cannot be created or destroyed, only transferred from one store to another or changed into a different form. The total energy of a closed system stays constant.

The proportion of the energy supplied to a device that is transferred usefully, often written as a percentage. The rest is usually lost as heat to the surroundings.

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

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

The force acting normally on each unit of area of a surface, measured in pascals. One pascal is one newton per square metre, and pressure increases if area decreases.

The mass of a substance per unit volume, measured in kilograms per cubic metre. It explains why some objects float and others sink in a liquid.

The extension of a spring is directly proportional to the force stretching it, provided the elastic limit is not exceeded. A force-extension graph is then a straight line through the origin.

The largest force or extension for which a material still returns to its original shape when the force is removed. Beyond it the material stays permanently deformed.

One of the agreed base units used worldwide in science, such as the metre, kilogram, second, ampere and kelvin. Other units are defined from these.

A word or symbol placed before a unit to show a multiple or fraction of it, such as kilo meaning a thousand or milli meaning a thousandth. It keeps numbers manageable.

The digits in a measured value that carry meaning about how precisely it was measured. A result should not be quoted with more significant figures than the data allow.

An error that causes repeated readings to scatter unpredictably above and below the true value. It can be reduced by taking several readings and calculating an average.

An error that shifts every reading in the same direction by the same amount, for example a balance that does not read zero. Repeating readings does not remove it.

How close a measured value is to the true value. It is affected by systematic errors, whereas precision describes how closely repeated readings agree with each other.

The energy needed to raise the temperature of one kilogram of a substance by one degree Celsius. Water has a high value, so it heats and cools slowly.

The energy absorbed or released when a substance changes state at constant temperature, such as melting or boiling. It breaks or forms bonds between particles rather than raising temperature.

The transfer of heat through a solid by particles passing on vibrations, without the material itself moving. Metals conduct well because free electrons also carry energy.

The transfer of heat in fluids by the movement of warmer, less dense material rising and cooler, denser material sinking. It cannot occur in solids.

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

The distance between two neighbouring points in phase on a wave, such as two crests. It is measured in metres and is linked to frequency and wave speed.

The change in direction of a wave as it passes from one medium to another because its speed changes. The frequency stays the same but the wavelength alters.

The complete reflection of a wave inside a denser medium when it meets a boundary beyond the critical angle. It is used in optical fibres to carry signals.

The current through a metallic conductor is directly proportional to the potential difference across it, provided temperature stays constant. Such a conductor has a constant resistance.

A measure of how hard it is for current to flow through a component, measured in ohms. It equals potential difference divided by current.

A circuit in which components are connected in a single loop, so the same current flows through each one. The supply voltage is shared between the components.

A circuit in which components are connected across separate branches, so the current divides between them. Each branch receives the full supply voltage.

The production of a potential difference in a conductor when it experiences a changing magnetic field, for example when a magnet is moved into a coil. Generators rely on this effect.

The time taken for half the unstable nuclei in a radioactive sample to decay, or for the count rate to halve. It is constant for a given isotope.

The force of gravity acting on each kilogram of mass at a point, measured in newtons per kilogram. On the Earth's surface its value is about ten newtons per kilogram.