GCSE Physics flashcards

About this deck

358 free AQA GCSE Physics flashcards across 9 topics. Every card is a key term and its definition, taken word for word from a published Revise Right lesson, and links back to that lesson so you can read the full notes behind it.

Energy

31 cards from 14 lessons. Each term links to the lesson it comes from.

Understanding Power

• Power: Power is the rate at which energy is transferred or the rate at which work is done. It is measured in watts (W).
• Watt: One watt equals one joule of energy transferred per second (1 W = 1 J/s).

Calculating Power

• Energy Transfer: The process by which energy moves from one store to another or one object to another. Always measured in joules (J) regardless of the energy type.
• Work Done: Energy transferred when a force causes movement. Calculated as force × distance moved in the direction of the force. Measured in joules (J).

Kinetic Energy Calculations

• Kinetic Energy: The energy stored in moving objects, calculated using Ek = ½mv². Measured in joules (J).
• Key physics definition: In Kinetic Energy Calculations, use precise GCSE terminology and units in every answer.

Elastic Potential Energy Calculations

• Elastic Potential Energy: Energy stored in a stretched or compressed elastic object that can be released when the object returns to its original shape. Measured in joules (J).
• Spring Constant (k): A measure of how stiff a spring is, defined as the force needed per unit extension. Measured in newtons per metre (N/m).
• Extension (e): The increase in length of a spring when a force is applied, measured from its natural length. Measured in metres (m).
• Limit of Proportionality: The point beyond which a spring no longer obeys Hooke's Law and extension is no longer proportional to force. The elastic potential energy formula only applies below this limit.

Gravitational Potential Energy Calculations

• Gravitational Potential Energy: The energy stored by an object due to its position in a gravitational field. Measured in joules (J).
• Gravitational Field Strength: The gravitational force per unit mass acting on an object. On Earth's surface, g = 9.8 N/kg (or 10 N/kg in calculations). Measured in newtons per kilogram (N/kg).
• Height: The vertical distance above a reference point, usually ground level. Measured in metres (m).

Specific Heat Capacity Explained

• Specific Heat Capacity: The amount of energy required to raise the temperature of one kilogram of a substance by one degree Celsius. Measured in joules per kilogram per degree Celsius (J/kg°C).

Energy Stores & Systems: Introduction

• System: An object or group of objects that we choose to study when analysing energy changes.

Energy Transfer Examples

• Energy Store: A way of describing where energy is located in a system. Common stores include kinetic, gravitational potential, elastic potential, chemical, and thermal energy stores.

Energy Transfer and Conservation

• Conservation of Energy: Energy cannot be created or destroyed, only transferred from one store to another or transformed from one form to another. The total energy in a closed system remains constant.
• Closed System: A system where no matter can enter or leave, allowing us to track all energy transfers within the system boundaries. The total energy remains constant.
• Energy Dissipation: The spreading out of energy to the surroundings, usually as thermal energy, making it less useful for doing work. Often described as 'wasted' energy.

Reducing Unwanted Energy Transfers

• Unwanted Energy Transfer: Energy that is transferred to the surroundings in a way that is not useful for the intended purpose, often as waste heat or sound.
• Lubrication: The use of substances like oil or grease to reduce friction between moving surfaces, thereby reducing unwanted energy transfers as heat.
• Thermal Conductivity: A property of materials that determines how quickly energy is transferred through them by conduction. Materials with high thermal conductivity transfer energy quickly.
• Thermal Insulation: Materials or methods used to reduce the rate of energy transfer by conduction, convection, or radiation. Good insulators have low thermal conductivity.

Calculating Efficiency

• Efficiency: The fraction of input energy that is transferred to useful output energy. It's always less than 1 (or 100%) because some energy is always wasted.

Increasing Efficiency

• Heat Loss: Unwanted thermal energy transfer from a system to its surroundings, reducing the useful energy available for the intended purpose
• Friction: The force that opposes motion between surfaces in contact, converting kinetic energy into heat energy

Energy Resources: An Overview

• Fossil Fuels: Energy sources formed from dead organisms buried and compressed over millions of years. Include coal, oil (petroleum) and natural gas.
• Nuclear Fuel: Uranium atoms that release enormous amounts of energy when split apart in nuclear reactors. One uranium pellet contains as much energy as a tonne of coal.
• Bio-fuel: Fuel made from recently living organisms like wood, crops, or waste. Renewable because new plants can be grown to replace those used.

Environmental Impact & Reliability

• Reliability: The ability of an energy resource to provide a consistent supply of energy when needed, regardless of weather or time conditions
• Environmental Impact: The effect that energy resource extraction, use and disposal has on the natural environment, including air, water and land pollution

Electricity

57 cards from 22 lessons. Each term links to the lesson it comes from.

Current, Potential Difference and Resistance

• Current (I): The rate of flow of electrical charge through a conductor, measured in amperes (A).
• Potential Difference (V): The energy transferred per unit charge between two points in a circuit, measured in volts (V). Also called voltage.
• Resistance (R): The opposition to the flow of current in a circuit component, measured in ohms (Ω).

Resistors in Series and Parallel

• Series Circuit: A circuit where components are connected end-to-end in a single loop, so the same current flows through each component.
• Parallel Circuit: A circuit where components are connected on separate branches, providing multiple paths for current to flow.
• Series and parallel resistance: In series, total resistance is the sum of the resistors. In parallel, the total resistance is always less than the smallest individual resistor.

Calculating Voltage, Current, and Resistance

• Voltage (Potential Difference): The energy transferred per unit charge between two points in a circuit, measured in volts (V). Symbol: V.
• Current: The rate of flow of electrical charge through a conductor, measured in amperes (A). Symbol: I.
• Resistance: The opposition to the flow of current in a circuit, measured in ohms (Ω). Symbol: R.

Measuring Resistance and Ohmic Conductors

• Ammeter: An instrument that measures electric current in amperes (A). It must be connected in series with the component being measured.
• Voltmeter: An instrument that measures potential difference in volts (V). It must be connected in parallel across the component being measured.
• Ohmic conductor: A component where current is directly proportional to potential difference at constant temperature. The resistance remains constant as current changes.

Non-Ohmic Components: Lamps and Diodes

• Non-ohmic component: A component whose resistance changes with the current flowing through it, so it does not obey Ohm's law.
• Filament lamp: A light bulb containing a thin wire filament that heats up and glows when current flows through it. The resistance increases as the filament gets hotter.
• Diode: A component that allows current to flow in only one direction. It has very high resistance in the reverse direction and low resistance in the forward direction above about 0.7V.
• I-V characteristic: A graph showing how current (I) varies with voltage (V) for a particular component. The shape reveals whether the component obeys Ohm's law.

Thermistors, LDRs, and Non-Linearity

• Thermistor: A temperature-dependent resistor whose resistance decreases as temperature increases. Made from semiconductor materials that become more conductive when heated.
• Light Dependent Resistor (LDR): A light-sensitive resistor whose resistance decreases as light intensity increases. Also called a photoresistor.
• Non-linear component: A circuit component that does not obey Ohm's law. Its current-voltage graph is not a straight line because resistance changes with voltage or current.

Circuit Symbols and Diagrams

• Battery: Represented by two parallel lines - one long (positive terminal) and one short (negative terminal). The long line always shows the positive end.
• Resistor: Shown as a rectangle. Opposes the flow of current and converts electrical energy to heat energy.
• Variable Resistor: A rectangle with an arrow through it. Allows you to change the resistance and control current flow.

Electric Charge and Current

• Potential Difference: The energy difference per unit charge between two points in a circuit. It's what 'pushes' current around the circuit.
• Electric Current: The rate of flow of electrical charge through a conductor. The size of the electric current is the rate of flow of electrical charge.

Series Circuits: Current, PD & Resistance

• Current in Series: The same current flows through each component in a series circuit. Current is not 'used up' by components.
• Potential Difference in Series: The total potential difference of the power supply is shared between the components in proportion to their resistance.
• Total Resistance in Series: The total resistance is the sum of all individual resistances: Rtotal = R1 + R2 + R3...

Series Circuits: Calculations, Design & Testing

• Equivalent Resistance: The single resistance value that could replace multiple resistors while maintaining the same current flow. In series circuits, equivalent resistance equals the sum of individual resistances.

Mains Electricity: Dangers and Precautions

• Mains electricity: The alternating current electrical supply to homes and buildings, operating at 230V and 50Hz in the UK.
• Live wire: The wire that carries current at 230V above earth potential in UK mains circuits, coloured brown in modern wiring.
• Earth potential: The electrical potential of the ground, defined as 0V, which provides a reference point for measuring all other voltages.
• Earth wire: A safety wire (coloured green and yellow) that connects appliance casings to earth, providing a low-resistance path for fault currents.

Three-Core Cables and Wire Identification

• Neutral wire: The wire that completes the circuit by providing a return path for current back to the supply. It remains at or close to earth potential (0V).

AC vs DC Potential Difference

• Direct Current (DC): Electric current that flows in one direction only, maintaining constant voltage over time. Measured in amperes (A).
• Alternating Current (AC): Electric current that repeatedly changes direction. In the mains supply, the potential difference also changes direction.
• Frequency: The number of complete AC cycles per second, measured in hertz (Hz). UK mains frequency is 50 Hz.

Energy Transfers in Appliances

• Power Rating: The rate at which an appliance transfers energy, measured in watts (W). It tells you how many joules of energy the appliance uses every second.
• Useful Energy Output: The energy that comes out of an appliance in the form you actually want, such as light from a bulb or movement from a motor.

Electrical Work and Energy Calculations (Part 1/2)

• Electrical Work: The energy transferred when electrical charge flows through a potential difference. Measured in joules (J).

Electrical Work and Energy Calculations (Part 2/2)

• Electrical Work Done: The energy transferred by an electrical current flowing through a component, measured in joules (J). It represents the conversion of electrical energy into other forms such as heat, light, or kinetic energy.
• Time: The duration for which current flows through a circuit, measured in seconds (s). Essential for calculating total energy transfer over a period.
• Charge Flow: The total amount of electrical charge that passes through a cross-section of a conductor, measured in coulombs (C). Related to current by Q = It.

National Grid Introduction

• National Grid: A system of cables and transformers linking power stations to consumers across the country.
• Power Station: A facility that generates electrical energy from various sources like fossil fuels, nuclear power, or renewable sources such as wind and solar.
• Transformer: A device that changes the voltage of alternating current electricity using electromagnetic induction.
• Consumer: End users of electricity including homes, schools, hospitals, factories and businesses that require electrical power for their operations.

Transformers and Efficiency in the National Grid

• Step-up transformer: A transformer that increases voltage from the primary coil to the secondary coil. The secondary coil has more turns than the primary coil.
• Step-down transformer: A transformer that decreases voltage from the primary coil to the secondary coil. The secondary coil has fewer turns than the primary coil.

Understanding Electrical Power

• Electrical Power: The rate of energy transfer in an electrical circuit. Measured in watts (W).
• Potential Difference (Voltage): The energy transferred per unit charge between two points in a circuit. Measured in volts (V).

Introducing Electric Fields

• Electric Field: A region around a charged object where other charged objects experience a force. The field exists even when no other charges are present to feel it.
• Field Lines: Imaginary lines that show the direction and strength of an electric field. They point away from positive charges and towards negative charges.

Electric Fields and Forces

• Non-contact Force: A force that acts between objects without them physically touching, transmitted through a field such as an electric field, magnetic field, or gravitational field.
• Electrostatic Force: The attractive or repulsive force between statically charged objects. The force decreases rapidly as the distance between the objects increases.
• Sparking: The sudden flow of electric charge through air when the electric field becomes strong enough to ionise air molecules and create a conducting path.

Producing Static Electricity

• Static electricity: Electric charge that builds up on insulating materials when they are rubbed together, caused by the transfer of electrons between surfaces.
• Electron transfer: The movement of negatively charged electrons from one material to another during rubbing, leaving one material positively charged and the other negatively charged.

Particle model of matter

28 cards from 12 lessons. Each term links to the lesson it comes from.

Changes of State: Mass Conservation and Reversibility

• Physical change: A change where no new substances are formed and the original properties can be recovered by reversing the change. The particles remain the same type but change their arrangement or energy.
• Conservation of mass: The principle that mass cannot be created or destroyed in any physical or chemical process. The total mass before equals the total mass after.
• Reversible change: A change that can be undone to restore the original material with its original properties. No new substances are formed during the process.

States of Matter and Density

• Particle Model: A scientific model that explains the behaviour of matter by describing how tiny particles move and interact in different states.
• States of Matter: The three main forms that matter can exist in: solid, liquid and gas, determined by particle arrangement and energy levels.
• Density: The mass per unit volume of a substance, calculated using density = mass ÷ volume, measured in kg/m³ or g/cm³.

Calculating Density

• Mass: The amount of matter in an object, measured in kilograms (kg).
• Volume: The amount of three-dimensional space occupied by an object, measured in cubic metres (m³).

Internal Energy: What's Inside?

• Internal Energy: The total kinetic energy and potential energy of all the particles (atoms and molecules) that make up a system.
• Kinetic Energy of Particles: The energy particles have due to their random motion. Faster moving particles have more kinetic energy.
• Potential Energy of Particles: The energy stored in the forces between particles. This depends on how far apart they are and how strongly they attract each other.

Understanding Specific Heat Capacity

• Temperature Change: The difference between final and initial temperatures, calculated as ΔT = T_final - T_initial.

Calculating Temperature Changes

• Thermal Energy Change (ΔE): The energy transferred when a substance changes temperature, measured in joules (J). It depends on the mass of the substance, its specific heat capacity, and the temperature change.
• Specific Heat Capacity (c): The amount of energy needed to raise the temperature of 1 kg of a substance by 1°C, measured in J/kg°C. Different materials have different specific heat capacities.
• Temperature Change (Δθ): The difference between final temperature and initial temperature, measured in degrees Celsius (°C). Always calculated as final temperature minus initial temperature.

Changes of State and Latent Heat

• Latent Heat: The energy needed for a substance to change state without changing temperature. Measured in joules (J).
• Specific Latent Heat: The amount of energy required to change the state of one kilogram of a substance with no change in temperature. Measured in joules per kilogram (J/kg).
• Specific Latent Heat of Fusion: Energy required to change 1 kg of solid to liquid (or liquid to solid) at the melting point. For water, this is 334,000 J/kg.
• Specific Latent Heat of Vaporisation: Energy required to change 1 kg of liquid to vapour (or vapour to liquid) at the boiling point. For water, this is 2,260,000 J/kg.

Work, Energy and Gas Pressure

• Work: The transfer of energy by a force when an object moves in the direction of the force. Measured in joules (J).
• Gas Pressure: The force per unit area exerted by gas particles colliding with container walls. Measured in pascals (Pa).

Pressure in Gases: Compression, Expansion, and Force

• Particle collision: The impact between a moving gas particle and a surface, transferring momentum and creating a force perpendicular to that surface.
• Compression: The process of reducing the volume of a gas by applying external pressure, forcing particles closer together and increasing collision frequency.
• Expansion: The process where a gas increases in volume when external pressure is reduced, allowing particles to spread out and reducing collision frequency.

Volume and Pressure

• Boyle's Law: For a fixed mass of gas at constant temperature, pressure multiplied by volume remains constant (P₁V₁ = P₂V₂)

Calculating Pressure and Volume Changes

• Pressure: The force per unit area exerted by gas particles colliding with container walls. Measured in pascals (Pa).

Gas Pressure, Temperature, and Kinetic Theory

• Kinetic Theory of Gases: A model that explains gas behaviour by considering gases as collections of tiny particles in constant, random motion.
• Average Kinetic Energy: The average kinetic energy of gas molecules. When temperature increases, the molecules have more kinetic energy on average.

Atomic structure

58 cards from 21 lessons. Each term links to the lesson it comes from.

Atomic Number, Mass Number, and Neutral Atoms

• Neutral Atom: An atom with equal numbers of protons and electrons, giving zero overall charge
• Atomic Number: The number of protons in the nucleus of an atom, which defines the element
• Mass Number: The total number of protons and neutrons in an atom's nucleus

Isotopes and Ion Formation

• Isotope: Atoms of the same element that have the same number of protons but different numbers of neutrons. They have the same atomic number but different mass numbers.
• Ion: An atom or group of atoms that has gained or lost electrons, giving it an overall electric charge. Positive ions have lost electrons; negative ions have gained electrons.

Early Atomic Models

• Early Atomic Model: Atoms were thought to be tiny, solid spheres that could not be divided into smaller parts. Each element had its own type of sphere with a specific mass.
• Electron: A negatively charged subatomic particle discovered by Thomson. About 1800 times lighter than a hydrogen atom and found in all elements.
• Plum Pudding Model: Thomson's model proposing that atoms are spheres of positive charge with negative electrons embedded in them, like raisins in a pudding.

The Nuclear Model

• Nuclear model: A model of the atom where most of the mass and all positive charge is concentrated in a tiny central nucleus, with electrons orbiting around it.
• Alpha particle scattering experiment: Rutherford's experiment where alpha particles were fired at thin gold foil to investigate atomic structure by observing how the particles were deflected.
• Scientific model: A simplified representation of reality used to explain observations and make predictions, which can be changed when new evidence emerges.

Refining the Model: Bohr and Chadwick

• Bohr Model: An atomic model where electrons orbit the nucleus at specific, fixed distances called energy levels or shells.
• Proton: A positively charged particle found in the nucleus, each carrying the same amount of positive charge.
• Neutron: A neutral particle found in the nucleus with approximately the same mass as a proton but no electrical charge.

Electron Arrangement and Energy Levels

• Energy levels: Fixed distances from the nucleus where electrons can exist. The first energy level (closest to nucleus) has the lowest energy, with energy increasing as you move further out.
• Electromagnetic radiation: Energy carried by waves including visible light, radio waves, microwaves, and X-rays. When absorbed by electrons, it provides the energy needed to move to higher energy levels.
• Ground state: The lowest energy arrangement of electrons in an atom, where all electrons occupy the lowest available energy levels. This is the most stable electron configuration.
• Excited state: When one or more electrons have absorbed energy and moved to higher energy levels than in the ground state. This is a temporary, unstable condition.

Radioactive Contamination and Irradiation

• Radioactive contamination: The unwanted presence of materials containing radioactive atoms on other materials. The hazard comes from the decay of the contaminating atoms.
• Irradiation: The process of exposing an object to nuclear radiation. The irradiated object does not become radioactive itself.
• Internal contamination: Radioactive material that enters the body through inhalation, ingestion, or wounds. Particularly dangerous because radiation is emitted directly inside body tissues.

Safety Precautions and Peer Review

• Ionising radiation: Radiation that has enough energy to remove electrons from atoms, creating ions. Can damage living cells and DNA.
• ALARA principle: As Low As Reasonably Achievable - the safety principle that radiation exposure should be kept to the minimum practical level.
• Contamination: The presence of unwanted radioactive material on surfaces, in air, or inside the body. Different from external radiation exposure.
• Peer review: The process where scientific research is evaluated by other experts in the same field before publication. Ensures accuracy and validity of findings.

Understanding Half-Life

• Half-life: The time taken for the number of nuclei of a radioactive isotope in a sample to halve, or for the count rate from a sample to fall to half its initial level.
• Random decay: The unpredictable nature of when individual radioactive nuclei will decay, though large samples follow predictable patterns.

Half-Life Calculations (HT)

• Activity: The rate at which radioactive nuclei decay in a sample. Measured in becquerels (Bq).
• Net decline: The total reduction in radioactive nuclei or activity over a given time period, often expressed as a ratio of final to initial values.

Alpha, Beta, Gamma, and Neutrons

• Alpha particle: A type of nuclear radiation consisting of two protons and two neutrons bound together, identical to a helium nucleus. Symbol: α or ⁴₂He.
• Beta particle: A high-speed electron ejected from the nucleus when a neutron transforms into a proton during radioactive decay. Symbol: β⁻ or e⁻.
• Gamma ray: Electromagnetic radiation emitted from an unstable nucleus to release excess energy. Gamma rays have no mass, no charge, and travel at the speed of light. Symbol: γ.
• Neutron radiation: Nuclear radiation consisting of free neutrons ejected from unstable nuclei. Neutrons have mass but no electrical charge. Symbol: n.

Radioactive Decay: Stability and Activity

• Nuclear instability: The condition where an atomic nucleus has an imbalance of protons and neutrons, making it likely to decay and emit radiation.
• Radioactive decay: A random process where unstable atomic nuclei emit radiation to become more stable. The timing of individual decays cannot be predicted.
• Count-rate: The number of radioactive decays detected per second by a radiation detector such as a Geiger-Muller tube, measured in counts per second.

Applications and Choosing Radiation Sources

• Penetrating power: The ability of radiation to pass through materials, determined by the type of radiation and energy of particles or photons. Alpha particles have low penetrating power (stopped by paper), beta particles have medium penetrating power (stopped by aluminium), and gamma rays have high penetrating power (reduced by lead).
• Ionising ability: The capacity of radiation to remove electrons from atoms, creating ions that can damage living tissue. Alpha particles have the highest ionising ability, beta particles have medium ionising ability, and gamma rays have the lowest ionising ability.

Understanding Nuclear Equations

• Nuclear equation: A symbolic representation of radioactive decay showing the parent nucleus, decay particle, and daughter nucleus with mass and atomic numbers balanced.

Nuclear Radiation in Medicine

• Medical tracer: A radioactive isotope that emits detectable radiation and can be tracked through the body to diagnose medical conditions. Usually attached to a compound that targets specific organs.
• Radiotherapy: Medical treatment using high-energy ionising radiation to damage the DNA of cancer cells, causing them to die. Can be delivered externally or internally.
• Gamma camera: Specialised medical imaging device that detects gamma rays emitted by radioactive tracers inside the patient's body to create images of organ function.

Evaluating Risks of Nuclear Radiation

• Risk: The combination of the probability of an event occurring and the severity of its consequences. Risk = Probability × Consequence.
• Background Radiation: Natural ionising radiation present in the environment from cosmic rays, naturally occurring radioactive elements in rocks and soil, and radon gas. Average UK exposure is 2.2 mSv per year.
• Probability: The likelihood that an event will occur, expressed as a fraction, decimal, or percentage. In risk assessment, probability is multiplied by consequence to calculate overall risk.

Sources of Background Radiation

• Cosmic Rays: High-energy particles from outer space that constantly bombard Earth's atmosphere, creating secondary radiation that reaches the ground.
• Terrestrial Radiation: Radiation from naturally occurring radioactive elements in rocks, soil, and building materials, particularly uranium, thorium, and radon gas.
• Nuclear Fallout: Radioactive particles released into the atmosphere from nuclear weapons testing or reactor accidents, which eventually settle on the ground and contribute to background radiation.

Radiation Dose and Measurement

• Radiation dose: A measure of the amount of ionising radiation absorbed by living tissue, taking into account the biological damage it can cause. Measured in sieverts (Sv).
• Sievert (Sv): The SI unit for measuring radiation dose, taking into account both the energy absorbed and the biological effectiveness of different types of radiation.
• Millisievert (mSv): One thousandth of a sievert (0.001 Sv). The unit commonly used for measuring typical radiation doses in medicine and occupational exposure.

Understanding Nuclear Fission

• Nuclear Fission: The splitting of a large, unstable nucleus (such as uranium-235 or plutonium-239) into two smaller nuclei of roughly equal size, releasing neutrons, gamma rays and enormous amounts of energy.
• Fission Fragments: The two smaller nuclei produced when a large nucleus undergoes fission. They are roughly equal in size but highly radioactive.
• Chain Reaction: A self-sustaining nuclear reaction where neutrons released by one fission event go on to trigger further fission events in nearby nuclei.

Energy Release and Chain Reactions

• Enough fissile material: Enough fissile material is needed to maintain a self-sustaining chain reaction. If there is not enough material, too many neutrons escape without causing fission.
• Control Rods: Rods made of neutron-absorbing materials that can be inserted into or withdrawn from a nuclear reactor core to control the rate of the chain reaction.

Introduction to Nuclear Fusion

• Nuclear Fusion: The joining of two light nuclei to form a heavier nucleus. In this process, some of the mass may be converted into the energy of radiation.
• Fusion energy release: Some mass may be converted into energy of radiation during fusion.

Forces

67 cards from 35 lessons. Each term links to the lesson it comes from.

Forces and Free Body Diagrams

• Force: A push or pull that acts on an object due to the interaction with another object. Measured in newtons (N).
• Free Body Diagram: A simplified diagram showing all the forces acting on a single object, represented as arrows pointing away from the object.
• Resultant Force: The single force that has the same effect as all the original forces acting together on an object. Measured in newtons (N).
• Balanced Forces: When all forces acting on an object cancel out completely, giving a resultant force of zero.

Calculating Resultant Forces

• Vector Addition: The process of combining forces by considering both their magnitude and direction to find the net effect.
• Force Resolution: Breaking down a single force into two component forces acting at right angles to each other.
• Equilibrium: The state when all forces acting on an object are balanced, resulting in zero resultant force.

(HT) Vector Diagrams and Resultant Forces

• Vector quantity: A physical quantity that has both a magnitude (size) and a direction. Force is a vector — you must always state how large it is AND which way it acts.

Introduction to Gravity and Weight

• Weight: The gravitational force acting on an object due to gravity, measured in newtons (N). Weight varies depending on gravitational field strength.
• Centre of Mass: The point where the total weight of an object can be considered to act. Also called the centre of gravity.

Scalar and Vector Quantities

• Scalar quantity: A physical quantity that has magnitude (size) only, with no associated direction. Examples include mass, temperature, speed, distance, and energy.
• Magnitude: The size or amount of a physical quantity, expressed as a numerical value with units. For vectors, magnitude is the length of the arrow when drawn to scale.

Introduction to Contact and Non-Contact Forces

• Contact Force: A force that acts when objects are physically touching each other. The force is transmitted through direct physical contact.

Forces as Vectors

• Newton's third law: When two objects interact, they exert equal and opposite forces on each other. The forces are the same size but act on different objects.

Introducing Work Done

• Displacement: The distance moved by an object in a particular direction. Measured in metres (m).

Calculating Work Done

• Joule: The unit of work done and energy. One joule is the work done when a force of one newton moves an object one metre in the direction of the force.
• Zero Work Scenarios: Situations where force is applied but no work is done: holding objects stationary, forces perpendicular to motion, or when objects don't move despite applied force.

Work Done Against Friction

• Work Done Against Friction: The energy transferred when a force overcomes friction between surfaces, resulting in a temperature rise of the object and its surroundings.
• Thermal Energy: The internal energy of an object due to the random motion of its particles, which increases when temperature rises.

Elasticity Explained: Forces, Deformation and Springs

• Deformation: A change in the shape or size of an object caused by applied forces. The object may stretch, compress, bend, or twist from its original form.
• Elastic deformation: Temporary change in shape where the object returns to its original form when the deforming forces are removed. The material stores energy during deformation.
• Inelastic deformation: Permanent change in shape where the object does not return to its original form when the deforming forces are removed. Energy is dissipated rather than stored.
• Hooke's Law: The extension of an elastic object is directly proportional to the applied force, provided the limit of proportionality is not exceeded. Mathematically: F = ke, where k is the spring constant.

Spring Constant and Calculations

• Spring Constant: A measure of the stiffness of a spring, defined as the force needed per unit extension. Measured in newtons per metre (N/m).
• Extension: The increase in length of a spring when a force is applied. Measured in metres (m).
• Elastic Limit: The maximum force that can be applied to a spring before it becomes permanently deformed and will not return to its original length.

Introduction to Moments

• Moment of a force: The turning effect of a force about a pivot point, measured in newton-metres (Nm).
• Pivot: The fixed point about which an object can rotate or turn.
• Perpendicular distance: The shortest distance from the pivot to the line of action of the force, measured at 90 degrees to the force direction.

Moments and Equilibrium

• Moment: The turning effect of a force about a pivot point, measured in newton metres (Nm).

Levers and Gears

• Lever: A rigid bar that pivots around a fixed point (fulcrum) to transmit forces. The lever multiplies effort by increasing the distance over which force is applied.
• Fulcrum: The fixed pivot point around which a lever rotates. The position of the fulcrum determines the mechanical advantage of the lever.
• Gear: A toothed wheel that meshes with other gears to transmit rotational motion and force. Gears can change speed, direction, or multiply torque.

Understanding Pressure in Fluids

• Fluid: A substance that can flow and take the shape of its container. This includes both liquids (like water, oil) and gases (like air, helium).
• Normal force: A force that acts perpendicular (at 90°) to a surface. In fluids, pressure always creates forces normal to surfaces.

Pressure in Liquid Columns

• Pressure in liquids: The force per unit area caused by the weight of liquid above a point, measured in pascals (Pa). Unlike gas pressure, liquid pressure increases linearly with depth.

Upthrust, Floating and Sinking

• Upthrust: The resultant upward force on a submerged object caused by pressure differences in the fluid. Measured in newtons (N).
• Archimedes' principle: The upthrust on an object equals the weight of fluid displaced by the object. This applies to any object in any fluid.

Modelling Atmospheric Pressure

• Atmospheric Pressure: The force per unit area exerted by the weight of air molecules in the atmosphere on a surface, measured in pascals (Pa) or millibars (mb)
• Atmosphere: A thin layer of gases surrounding Earth, held in place by gravity and becoming less dense with increasing altitude
• Air Density: The mass of air per unit volume, which decreases with altitude as air molecules become more spread out

Distance, Displacement and Speed (Part 1/3)

• Distance: The total length of the path travelled by an object. Distance is a scalar quantity — it has magnitude (size) but no direction. Measured in metres (m).
• Speed: The rate at which distance is covered. Speed is a scalar quantity with no direction. It is calculated as distance divided by time. For this lesson, if distance is measured in metres (m) and time is measured in seconds (s), then speed is measured in metres per second (m/s).

Distance, Displacement and Speed (Part 2/3)

• Constant speed: Motion where an object covers equal distances in equal time intervals.
• Average speed: Average speed is total distance travelled divided by total time taken.

Distance, Displacement and Speed (Part 3/3)

• Velocity: The speed of an object in a given direction, measured in metres per second (m/s) in a specified direction.

Velocity, Distance-Time Graphs and Speed

• Distance-time graph: A graph showing how the total distance travelled changes with time, where the gradient (slope) at any point represents the speed at that moment.

Acceleration, Velocity-Time Graphs and Terminal Velocity (Part 1/3)

• Acceleration: The rate of change of velocity, measured in metres per second squared (m/s²). It tells us how quickly velocity increases or decreases.
• Velocity-time graph: A graph showing how velocity changes over time. The y-axis shows velocity (m/s), the x-axis shows time (s), and the gradient of the line represents acceleration.
• Terminal velocity: The constant maximum velocity reached by a falling object when the drag force equals the gravitational force. At this point, acceleration becomes zero.

Acceleration, Velocity-Time Graphs and Terminal Velocity (Part 2/3)

• Uniform acceleration: Motion where the acceleration remains constant throughout. This allows us to use the kinematic equations like v² - u² = 2as.

Acceleration, Velocity-Time Graphs and Terminal Velocity (Part 3/3)

• Drag Force: The force that opposes motion through a fluid, caused by friction between the object and fluid particles. Increases with speed and depends on the object's shape and surface area.

Newton's First Law of Motion

• Newton's First Law of Motion: If the resultant force acting on an object is zero, then: (1) a stationary object remains stationary, (2) a moving object continues to move at the same speed in the same direction (constant velocity).
• Inertia: The tendency of objects to continue in their state of rest or of uniform motion. Objects 'resist' changes to their motion.
• Inertial Mass: A measure of how difficult it is to change the velocity of an object. Mathematically defined as the ratio of force to acceleration (m = F/a).

Newton's Second Law: F = ma (Part 1/2)

• Newton's Second Law: The acceleration of an object is proportional to the resultant force acting on it and inversely proportional to its mass.

Newton's Second Law: F = ma (Part 2/2)

• Approximately equal (~): A symbol meaning a value is close to, but not exactly equal to, another value. In GCSE physics it is often used when 9.8 N/kg is rounded to 10 N/kg for simpler calculations.

Newton's Third Law: Action and Reaction

• Action-reaction pair: Two forces that are equal in magnitude, opposite in direction, and act on different objects during an interaction.

Thinking Distance

• Thinking Distance: The distance travelled by a vehicle during the driver's reaction time, before the brakes are applied. Measured in metres.
• Reaction Time: The time taken for a driver to respond to a hazard after seeing it. Typical values range from 0.2 to 0.9 seconds.
• Typical Reaction Times: Alert driver: 0.2-0.4 seconds. Tired driver: 0.5-0.7 seconds. Impaired driver: 0.7-0.9 seconds or more.

Braking Distance

• Braking Distance: The distance a vehicle travels from when the brakes are applied until it comes to a complete stop, measured in metres (m).
• Deceleration: The rate at which a vehicle slows down when braking, measured in metres per second squared (m/s²). It's negative acceleration.

Force, Momentum and Acceleration

• Momentum: The product of an object's mass and velocity, measured in kg m/s. Momentum = mass × velocity.
• Rate of change of momentum: How quickly momentum changes over time, measured in kg m/s². This equals the net force acting on an object.

Momentum and Safety Features

• Momentum change: The change in momentum of an object, equal to force multiplied by time (change in momentum = F × t). Measured in N s, which is equivalent to kg m/s.

Introduction to Momentum Conservation

• Conservation of Momentum: In a closed system, the total momentum before an event equals the total momentum after the event. Mathematically: momentum before = momentum after

Waves

49 cards from 18 lessons. Each term links to the lesson it comes from.

Ultrasound and Echo Sounding

• Ultrasound: Sound waves with frequencies above the upper limit of human hearing (above 20,000 Hz). Used for medical imaging and industrial testing.
• Partial reflection: When ultrasound waves meet a boundary between different materials, some of the wave energy is reflected back whilst some continues through.
• Echo sounding: A technique using high frequency sound waves to detect objects in deep water and measure water depth by timing reflections.

Seismic Waves and Earth's Structure

• Seismic waves: Energy waves produced by earthquakes that travel through Earth's layers, carrying information about the planet's internal structure.
• P-waves: Longitudinal seismic waves that compress and stretch material as they travel. They can pass through both solids and liquids at different speeds.
• S-waves: Transverse seismic waves that shake material from side to side. They cannot travel through liquids because liquids cannot support shear forces.

Wave Properties for Detection and Exploration

• Wave velocity in materials: The speed at which waves travel through different substances. Sound waves travel faster through solids than liquids, and faster through liquids than gases.
• Wave absorption: The process where materials convert wave energy into other forms of energy (usually heat). Soft, less dense materials typically absorb more wave energy than hard, dense materials.
• Wave reflection at boundaries: The bouncing back of waves when they encounter a change in material properties. The greater the difference between materials, the stronger the reflection.

Wave Characteristics: Amplitude, Wavelength & Frequency

• Amplitude: The maximum displacement of a point on a wave away from its undisturbed position.
• Wavelength: The distance from a point on one wave to the equivalent point on the adjacent wave.

Measuring Wave Speed: Sound and Water

• Wave Speed: The speed at which energy is transferred through a medium by a wave, measured in metres per second (m/s).
• Echo Method: A technique for measuring sound speed by timing how long sound takes to travel to a surface and back.
• Ripple Tank: Laboratory apparatus used to generate and observe water waves for measuring wave properties including speed.

Sound Waves and Vibrations

• Sound Wave: A longitudinal wave that travels through materials by causing particles to vibrate back and forth parallel to the direction of wave travel. Measured in hertz (Hz) for frequency and metres per second (m/s) for speed.
• Vibration: Rapid back and forth movement of particles or objects about their rest position. In solids, this movement can be transmitted through the material structure.
• Frequency Range: The span of frequencies that can be detected or transmitted, measured in hertz (Hz). For human hearing, this is approximately 20 Hz to 20,000 Hz.

The Human Hearing Range

• Human Hearing Range: The range of sound frequencies that can be detected by the human ear, from 20 Hz to 20 kHz (20,000 Hz).
• Infrasound: Sound waves with frequencies below 20 Hz, beneath the lower limit of human hearing. Often felt as vibrations rather than heard.

Producing and Absorbing Radio Waves and Gamma Rays

• Oscillating circuit: An electrical circuit containing components that cause current to alternate direction at regular intervals, producing electromagnetic waves.
• Induced current: An alternating electrical current created in a conductor when it is exposed to changing electromagnetic fields, with the same frequency as the inducing wave.
• Nuclear transition: A change in the energy state of an atomic nucleus, often accompanied by the emission of electromagnetic radiation such as gamma rays.

Hazards of UV, X-rays, and Gamma Rays

• Ultraviolet radiation: Electromagnetic waves with frequencies higher than visible light but lower than X-rays. UV radiation can damage skin cells and increase cancer risk.

Visible Light: Absorption, Reflection, and Transmission

• Absorption: The process by which an object takes in light energy and converts it to other forms, typically heat. Absorbed wavelengths are not reflected back to our eyes.
• Reflection: The bouncing back of light from a surface. The wavelengths that are strongly reflected determine the colour we see.
• Transmission: The passage of light through a material. Objects that transmit light are either transparent or translucent.
• Opaque: A material that does not allow light to pass through it. Light is either absorbed or reflected, never transmitted.

Colour Filters & Wavelengths

• Visible light spectrum: The range of electromagnetic radiation that human eyes can detect, with wavelengths from approximately 400nm (violet) to 700nm (red)
• Specular reflection: Reflection from a smooth surface in a single direction, producing clear images like those seen in mirrors
• Diffuse reflection: Reflection from a rough surface that scatters light in many directions, allowing objects to be seen from multiple angles
• Colour filter: A transparent material that absorbs certain wavelengths of light whilst transmitting others, changing the apparent colour of objects viewed through it

Convex and Concave Lenses

• Refraction: The bending of light when it passes from one material to another due to a change in speed.
• Principal focus: The point where parallel rays of light converge after passing through a convex lens.
• Focal length: The distance from the centre of a lens to its principal focus, measured in centimetres.
• Virtual focus: The point from which diverging rays appear to come when traced backwards through a concave lens.

Ray Diagrams

• Convex lens: A lens that is thicker in the middle than at the edges, causing parallel light rays to converge to a focal point.
• Concave lens: A lens that is thinner in the middle than at the edges, causing parallel light rays to diverge as if coming from a focal point.

Magnification

• Magnification: The ratio of image height to object height, showing how many times larger an image appears compared to the actual object. Magnification has no units because it is a ratio.
• Image height: The measured height of the magnified image as it appears through the lens or on a screen. This is what you can physically measure with a ruler.
• Object height: The actual height of the real specimen or object being observed. This is the true size before any magnification occurs.

Radio Waves, Microwaves and Infrared

• Radio waves: Electromagnetic waves with wavelengths from about 1 metre to several kilometres, and frequencies from about 300 MHz down to 3 kHz. They are used for television and radio broadcasting because they can travel long distances through the atmosphere.
• Microwaves: Electromagnetic waves with wavelengths from about 30 cm down to 1 millimetre, and frequencies from about 300 MHz to 300 GHz. They are used for satellite communications and cooking food because they can penetrate the atmosphere and are absorbed by water molecules.
• Infrared radiation: Electromagnetic waves with wavelengths from about 1 millimetre down to 700 nanometres, and frequencies from about 300 GHz to 430 THz. They are used for electrical heaters, cooking food, and infrared cameras because all warm objects emit infrared radiation.

Infrared Radiation: Emission and Absorption

• Perfect black body: An idealised object that absorbs all incident radiation and reflects or transmits none. Since good absorbers are also good emitters, a perfect black body is the best possible emitter of radiation.

Emission and Absorption

• Black body radiation: Electromagnetic radiation emitted by all objects due to their temperature, with intensity and wavelength distribution dependent on the object's temperature.
• Intensity: The amount of energy transferred per unit area per unit time, measured in watts per square metre (W/m²).
• Thermal equilibrium: The state where an object absorbs radiation at the same rate as it emits radiation, maintaining constant temperature.

Earth's Temperature and Radiation Balance

• Radiation Balance: The equilibrium between incoming radiation absorbed by a body and radiation emitted by that body, which determines its temperature.
• Emission: The process by which a body releases electromagnetic radiation due to its temperature.

Magnetism and electromagnetism

35 cards from 17 lessons. Each term links to the lesson it comes from.

Magnetic Poles and Forces

• Magnetic pole: The regions of a magnet where the magnetic forces are strongest, located at the ends of bar magnets.
• Magnetic attraction: The force that pulls unlike magnetic poles (north and south) towards each other.
• Magnetic repulsion: The force that pushes like magnetic poles (north-north or south-south) away from each other.

Permanent vs. Induced Magnets

• Permanent magnet: A material that produces its own magnetic field without needing an external magnetic field. The magnetism persists indefinitely under normal conditions.
• Induced magnet: A material that becomes magnetic only when placed in a magnetic field. When removed from the magnetic field, an induced magnet loses most or all of its magnetism quickly.

Introduction to Magnetic Fields

• Magnetic field: The region around a magnet where a force acts on another magnet or on a magnetic material (iron, steel, cobalt and nickel).
• Magnetic attraction rule: The force between a magnet and a magnetic material is always one of attraction.
• Magnetic field strength variation: The strength of the magnetic field depends on the distance from the magnet. The field is strongest at the poles of the magnet.
• Magnetic field direction: The direction of the magnetic field at any point is given by the direction of the force that would act on another north pole placed at that point. The direction of a magnetic field line is from the north (seeking) pole of a magnet to the south (seeking) pole of the magnet.

Plotting Magnetic Field Patterns

• Magnetic field lines: Imaginary lines that show the direction of magnetic force. They run from north pole to south pole and never cross each other.
• Compass: A device containing a small magnetised needle that aligns with magnetic field lines to show direction.

Earth's Magnetic Field and Compasses

• Magnetic compass: A navigation instrument containing a small bar magnet that aligns with Earth's magnetic field to indicate direction.
• Earth's magnetic field: The magnetic field generated by Earth's molten iron core, extending from the magnetic north pole to the magnetic south pole.

Understanding Electric Motors

• Motor Effect: The force experienced by a current-carrying conductor when placed in a magnetic field. The force is perpendicular to both the current direction and magnetic field direction.
• Fleming's Left-Hand Rule: A method to predict the direction of force on a current-carrying conductor in a magnetic field using the left hand. First finger = Field direction, seCond finger = Current direction, thuMb = Motion direction.
• Commutator: A split-ring device in an electric motor that reverses the current direction in the coil every half turn. This ensures continuous rotation in the same direction by maintaining the correct force directions.

Factors Affecting Force on a Conductor

• Magnetic Flux Density: A measure of the strength of a magnetic field, measured in tesla (T). A tesla (T) is the unit used for magnetic flux density.

Currents and Magnetic Fields

• Solenoid: A coil of wire that produces a strong, uniform magnetic field when current flows through it. The field pattern resembles that of a bar magnet with distinct north and south poles.
• Right-hand rule: A method to determine the direction of the magnetic field around a current-carrying conductor. Point your right thumb in the direction of conventional current flow, and your fingers curl in the direction of the magnetic field lines.

Solenoids and Electromagnets

• Electromagnet: A solenoid with an iron core that can be switched on and off by controlling the electric current.

Loudspeakers and Headphones: Converting Electricity to Sound

• Moving-Coil Loudspeaker: An electromagnetic device that converts varying electrical signals into sound waves by using the motor effect to vibrate a cone that creates pressure variations in air.
• Frequency Response: The range of sound frequencies that an audio device can accurately reproduce, typically measured in hertz (Hz) from low bass to high treble.

The Generator Effect

• Generator Effect: If an electrical conductor moves relative to a magnetic field, or if there is a change in the magnetic field around a conductor, a potential difference is induced across the ends of the conductor. If the conductor is part of a complete circuit, a current is induced in the conductor.
• the induced current opposes the change that caused it: An induced current generates a magnetic field that opposes the original change, either the movement of the conductor or the change in magnetic field. This ensures energy conservation in electromagnetic systems.

Factors Affecting Induced Potential

• Changing magnetic field: A potential difference is induced when a conductor cuts across magnetic field lines or when the magnetic field through the conductor changes.

Microphones and the Generator Effect

• Moving-coil Microphone: A transducer that converts sound waves into electrical signals using the generator effect. It consists of a coil of wire attached to a diaphragm, positioned within a permanent magnetic field.
• Electromagnetic Induction: The process by which a changing magnetic field or relative motion between a conductor and magnetic field generates an electrical current. The induced voltage is proportional to the rate of change of magnetic flux.

AC and DC Generators

• Alternator: A type of AC generator that uses the generator effect to produce alternating current by rotating a coil in a magnetic field.
• Dynamo: A type of DC generator that uses the generator effect with a commutator to produce direct current from rotating motion.

Interpreting Generator Graphs

• smooth repeating wave: A smooth wave pattern that repeats regularly, characteristic of alternating current generated by rotating coils. The voltage changes as the coil rotates.
• Peak voltage: The maximum potential difference reached during one complete cycle of alternating current generation. This occurs when the coil sides are cutting through magnetic field lines at maximum rate.

Introduction to Transformers

• Primary Coil: The input coil of a transformer that is connected to the alternating current supply. Creates a changing magnetic field in the iron core when AC flows through it.
• Secondary Coil: The output coil of a transformer where the induced voltage appears. The voltage depends on the ratio of turns compared to the primary coil.

Transformer Efficiency and Power

• Ideal transformer: A theoretical transformer with 100% efficiency where all electrical power input equals electrical power output, with no energy losses to heat, sound, or magnetic flux leakage.
• Transformer efficiency: The percentage of input power that is successfully transferred to the output, calculated as (Power Output ÷ Power Input) × 100%. Typical values range from 95% to 99% for power transformers.

Space physics (physics only)

25 cards from 8 lessons. Each term links to the lesson it comes from.

Formation of the Solar System

• Nebula: A vast cloud of dust and gas in space, typically hundreds of light-years across, containing the raw materials for star formation. Composed mainly of hydrogen and helium with traces of heavier elements.
• Gravitational collapse: The process by which matter falls inward under gravity, causing compression and heating.
• Balanced state: The Sun is stable because inward gravity is balanced by energy from fusion.

Components of Our Solar System

• Planet: A celestial body that orbits the Sun, has sufficient mass to be roughly spherical, and has cleared its orbital neighbourhood of other objects.
• Natural Satellite: A celestial body that orbits a planet or other larger body, held in orbit by gravitational forces. Also called a moon.
• Galaxy: A massive collection of stars, gas and dust bound together by gravity. Our galaxy is the Milky Way.
• Dwarf Planet: A celestial body that orbits the Sun and has sufficient mass to be roughly round, but has not cleared its orbital neighbourhood of other objects.

Star Size and Life Cycle

• Solar mass: The mass of our Sun, used as a standard unit for measuring stellar masses. Equal to approximately 2 × 10³⁰ kg.
• Main sequence: The stable phase of a star's life when it fuses hydrogen into helium in its core, lasting billions of years for Sun-like stars.
• Supernova: The explosive death of a massive star when its core collapses and spreads elements into space.
• Massive star end state: A black hole is an object with gravity so strong that even light cannot escape.

Fusion, Supernova and Element Creation

• Fusion in stars: The nuclear fusion processes occurring in stars that create new elements from hydrogen and helium. This process builds elements up to iron through successive fusion reactions in stellar cores.
• Heavy Elements: Elements heavier than iron are produced in supernovae.

Circular Orbits and Gravity

• Centripetal force: The force directed towards the centre of a circular path that keeps an object moving in a circle, measured in newtons (N).
• Gravitational force: The attractive force between any two masses, proportional to both masses and inversely proportional to the square of the distance between them, measured in newtons (N).
• Stable orbit: A stable orbit is an orbit where gravity keeps the object moving in a circle.

Planets, Moons, and Satellites

• Gravity: The attractive force between any two masses that acts towards the centre of mass. Measured in newtons (N).
• Orbit: The curved path that an object follows around another object due to gravitational attraction. Can be circular or elliptical.
• Artificial Satellite: A human-made object placed in orbit around Earth or another celestial body for scientific, communication, or navigation purposes.

Red-Shift and the Expanding Universe

• Red-shift: The observed increase in wavelength of electromagnetic radiation from distant galaxies moving away from us. The light appears more red than expected.
• Red-shift idea: The increase in wavelength of light from a galaxy moving away from the observer.
• Expanding universe: The scientific theory that space itself is getting larger over time, causing galaxies to move apart from each other.
• Big Bang theory: The scientific model explaining how the universe began from an extremely hot, dense state approximately 13.8 billion years ago and has been expanding and cooling ever since.

The Big Bang: Evidence and Expansion

• Dark matter: Invisible matter that makes up about 27% of the universe, detected only through its gravitational effects on visible matter.
• Dark energy: Scientists do not yet fully understand dark mass and dark energy.

Key ideas

8 cards from 3 lessons. Each term links to the lesson it comes from.

Models and Cause & Effect

• Wave Model: A model that describes energy transfer through oscillations without transferring matter. Used to explain the behaviour of light and sound.
• Cause and Effect: The relationship where one event (cause) directly leads to another event (effect). Used to explain why changes occur in scientific systems.

Action at a Distance and Drivers of Change

• Action at a Distance: The ability of objects to exert forces on each other without physical contact, mediated through fields. Examples include gravitational attraction, magnetic forces, and electrostatic forces.
• Field: A region of space where an object experiences a force due to the presence of another object, even without direct contact. The field strength decreases with distance from the source.
• Gradient: The rate of change of a quantity over distance. In fields, gradients determine the strength of forces — steep gradients create strong forces.

Proportionality and Maths in Physics

• Direct proportionality: A relationship where two quantities increase or decrease together at a constant rate. If one doubles, the other doubles. Written as y ∝ x or y = kx where k is the constant of proportionality.
• Inverse proportionality: A relationship where one quantity increases as the other decreases, such that their product remains constant. Written as y ∝ 1/x or xy = k where k is constant.
• Mathematical model: An equation that describes the relationship between physical quantities, allowing predictions and calculations to be made about real-world situations.