Physics Level 4 key terms

A quantity that has size only, with no direction. Mass, time, speed, and temperature are examples, and ordinary arithmetic combines them directly.

A quantity with both size and direction, such as force, velocity, or displacement. Vectors add tip-to-tail rather than by simple arithmetic, so direction must be stated with the answer.

The size or amount of a quantity, ignoring its direction. For a vector it is the length of the arrow representing it, and it is never negative.

The single vector that has the same effect as two or more vectors combined. It is found by drawing them tip-to-tail or by resolving them into perpendicular components.

The part of a vector acting along one chosen direction, usually horizontal or vertical. Adding the components of all vectors gives the resultant in each direction.

Splitting a single vector into two perpendicular components using trigonometry. A force F at angle theta to the horizontal has components F cos theta horizontally and F sin theta vertically.

The straight-line distance and direction from a starting point to a finishing point. It differs from distance travelled, which counts the whole path and has no direction.

Rate of change of displacement, a vector measured in metres per second. Its direction matters, so a car going round a bend at steady speed still changes velocity.

Rate of change of velocity, measured in metres per second squared. An object accelerates when its speed changes, its direction changes, or both change together.

An object stays at rest or moves at constant velocity unless a resultant force acts on it. It describes inertia and explains why seat belts and headrests matter in vehicles.

The resultant force on an object equals its mass times its acceleration, F = ma. For a fixed force, a larger mass gives a smaller acceleration.

If one body exerts a force on another, the second exerts an equal and opposite force on the first. These paired forces act on different bodies, so they never cancel out.

The single force that replaces all the forces acting on a body, found by vector addition. A zero resultant means the forces are balanced and velocity does not change.

A sketch of a single object with arrows showing every external force acting on it, labelled with sizes and directions. It is the starting point for applying Newton's laws.

The state of a body when the forces on it balance, giving zero resultant force and zero resultant moment. It may be at rest or moving at constant velocity.

The turning effect of a force, calculated as force multiplied by the perpendicular distance from the pivot, measured in newton metres. A longer spanner gives a bigger moment for the same force.

For a body in equilibrium, the total clockwise moment about a pivot equals the total anticlockwise moment. It is used to solve balance and lever problems.

The point through which the whole weight of an object appears to act. An object balanced on a support directly below this point stays in stable equilibrium.

How hard it is to topple an object. 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.

Energy transferred when a force moves an object along its line of action, calculated as force times distance moved, measured in joules.

The rate at which energy is transferred or work is done, measured in watts, where one watt is one joule per second. Power equals work done divided by time taken.

The fraction of energy supplied that is transferred usefully, often written as a percentage. It equals useful output energy divided by total input energy, multiplied by one hundred.

The energy an object has because of its motion, calculated as one half times mass times speed squared. Doubling the speed quadruples the kinetic energy.

Energy stored in an object because of its height in a gravitational field, calculated as mass times gravitational field strength times height. It is gained when an object is lifted.

Energy cannot be created or destroyed, only transferred between stores or transformed into other forms. The total energy of a closed system stays constant.

The extension of a spring is directly proportional to the force applied, provided the limit of proportionality is not exceeded. The constant of proportionality is the spring constant.

The force needed to stretch a spring by one metre, measured in newtons per metre. A stiff spring has a large spring constant and extends less for a given load.

The maximum force or extension for which a material returns to its original shape when the load is removed. Beyond it, the material is permanently deformed.

A permanent change of shape that remains after the deforming force is removed. It happens when a material is stretched past its elastic limit.

The increase in length of a spring or wire when a load is applied, found by subtracting the original length from the stretched length. It is measured in metres.

The variable the experimenter deliberately changes between readings, such as the load hung on a spring. It is plotted on the horizontal axis of a graph.

The variable that is measured for each change of the independent variable, such as the extension of a spring. It is plotted on the vertical axis.

A factor kept the same throughout an experiment so it cannot affect the result, such as using the same spring each time. Controlling variables makes comparisons fair.

An investigation in which only the independent variable is changed while all other relevant factors are kept constant, so any effect on the outcome can be attributed to that change.

How close a measured value is to the true value. Accuracy is improved by using better instruments and removing systematic errors, not simply by repeating readings.

How close repeated measurements are to each other, and how finely an instrument can read. Precise readings may still be inaccurate if there is a systematic error.

The smallest change in a quantity that an instrument can detect, such as one millimetre on a ruler. A finer resolution reduces the uncertainty of a single reading.

A consistent error that shifts all readings in the same direction, caused for example by a zero error or a mis-calibrated instrument. Repeating readings does not remove it.

An unpredictable variation in readings caused by factors such as reaction time or fluctuating conditions. It is reduced by taking repeats and calculating a mean.

A reading shown by an instrument when the true value is zero, such as a balance that reads 0.2 g with nothing on it. It must be subtracted from every reading.

The extent to which an experiment gives consistent results when repeated. Taking repeat readings and averaging them, or plotting a best-fit line, improves reliability.

Whether an experiment actually measures what it claims to measure. It requires controlling relevant variables and choosing a method that suits the question being asked.

A result that does not fit the pattern of the other readings, often caused by a mistake or a one-off disturbance. It is identified and excluded from the mean.

The range within which the true value is likely to lie, often estimated as half the smallest scale division for a single reading. It is stated with the final result.

A straight line or smooth curve drawn through the centre of a set of plotted points so that points are scattered evenly on both sides. It reveals the trend and allows prediction.

The steepness of a graph line, found by dividing the change in the vertical quantity by the change in the horizontal quantity. Its units come from the axes.

A plot of the dependent variable against the independent variable, used to show the relationship between them. Axis labels, units, and a sensible scale are essential.

An electronic device that records measurements from sensors at set intervals and stores them for analysis. It reduces reaction-time error and can capture fast changes.

A careful review of an experiment that identifies hazards, decides how likely and how serious each is, and states the precautions taken to reduce the risk.

Anything in an experiment that could cause harm, such as a hot surface, a falling mass, or a chemical. Identifying hazards is the first step of a risk assessment.

A practical action taken to reduce a hazard, such as clamping a stand, wearing goggles, or standing clear of a swinging pendulum. Precautions are recorded in the risk assessment.