Key term
OCR GCSE Physics A J249
Electricity
Topic overviewCharge, and producing static electricityTransfer of electrons, and electric fieldsCurrent as a rate of flow of chargeCharge, current and timeSeries and parallel circuits, and circuit symbolsCurrent, potential difference and resistanceResistors whose resistance changes, and investigating themLinear and non-linear circuit elements from graphsNet resistance in series and parallelCircuits for measurement, and electrical power
Energy
Topic overviewConservation of energy, and energy storesEnergy changes on heating, and calculating themEnergy of a moving body, a spring and a raised objectDissipation, and energy transfer in domestic devicesPower ratings, efficiency, and increasing itReducing unwanted energy transfer, and the rate of cooling
Forces
Topic overviewMeasuring distance and time, and calculating speedConverting units, and ratesVectors and scalars in motionDistance-time and velocity-time graphsAverage speed, and the equations of uniform motionHow objects interact, and forces as vectorsNewton's first lawResolving forces, and free body diagramsResultant forces, and balanced forcesNewton's second law, and inertiaMomentum, and force as a change in momentumWork done, and stored energyPower, and Newton's third lawCircular motion and changing velocityStretching, bending and compressing; elastic and plasticForce and extension, linear and non-linearThe spring constant, and work done in stretchingGravitational fields, weight and free fallCalculations with weight and gravitational field strengthTurning forces and the moment of a forceLevers and gearsPressure in fluids, and the force on a surface
Global Challenges
Topic overviewTypical speeds and everyday accelerationsReaction time, stopping distance and the dangers of large decelerationsEstimating stopping distances and the forces in a collisionEnergy resources, and trends in their useThe national grid, and step-up and step-down transformersWhy the national grid is efficient, and the transformer equationMains electricity: a.c., d.c. and the domestic supplyLive, neutral and earth wires, and electrical dangerRed-shift and the Big BangThe formation of the Sun, and radiation from bodiesThe solar systemCircular orbits and stable orbitsRadiation and the temperature of a body, and seismic waves and sonar
Magnetism and Magnetic Fields
Topic overviewPermanent and induced magnets, and magnetic polesMagnetic fields, and the dipping compassThe magnetic effect of a current, and solenoidsThe motor effect and Fleming's left-hand ruleThe force on a conductor, and how a motor turnsInduced potential, alternators and dynamosTransformers and the turns ratioThe microphone
Matter
Topic overviewHow the atomic model changed, and the structure of the atomThe size of atoms, and defining densityDensity of the states of matter, and density calculationsConservation of mass in changes of stateHeating a system, and specific heat capacityCalculations with specific heat capacity and latent heatGas molecules, temperature and pressureCompressing a gas, and changing its volumeDoing work on a gasAtmospheric pressure and why it varies with heightFloating, sinking and pressure in a liquid
Radioactivity
Topic overviewProtons, neutrons and isotopesUnstable nuclei and the emissions they give outBalancing nuclear equationsElectron energy levels, and radiation from atomsHalf-life and the randomness of decayPenetration of alpha, beta and gammaContamination and irradiation, and half-life as a hazardUses of nuclear radiationNuclear fission and fusion
Waves in Matter
Topic overviewAmplitude, wavelength, frequency and periodThe wave equationTransverse and longitudinal wavesSound crossing a boundary; reflection, transmission and absorptionConverting sound to vibrations, and the range of hearingModelling waves with ripples and soundElectromagnetic waves as transverse, and energy transferFrequency and wavelength across the spectrumWhat our eyes detect, and light as an electromagnetic waveUses of electromagnetic wavesHazards of ultraviolet, X-rays and gamma raysExploring structures with waves, and producing radio wavesAbsorption, transmission, refraction and reflectionRay diagrams for reflection and refractionHow colour arises
Forces
- 22 subtopics
- 45 things to know
- Paper 3
What Forces covers
Forces is examined in Physics A Paper 3. It covers measuring distance and time, and calculating speed; converting units, and rates; vectors and scalars in motion; distance-time and velocity-time graphs; average speed, and the equations of uniform motion; how objects interact, and forces as vectors; Newton's first law; resolving forces, and free body diagrams; resultant forces, and balanced forces; Newton's second law, and inertia; momentum, and force as a change in momentum; work done, and stored energy; power, and Newton's third law; circular motion and changing velocity; stretching, bending and compressing: elastic and plastic; force and extension, linear and non-linear; the spring constant, and work done in stretching; gravitational fields, weight and free fall; calculations with weight and gravitational field strength; turning forces and the moment of a force; levers and gears; and pressure in fluids, and the force on a surface.
Where it is assessed
Paper 3
Physics A Paper 3: 1 hour 45 minutes, 90 marks, 50% of the GCSE.
Check the OCR specification ↗The 22 subtopics
Each one has its own page.
- Measuring distance and time, and calculating speedInstruments for measuring length and time, why light gates beat a hand-held stopwatch, how reaction time is reduced, and finding speed from distance, time and the gradient of a distance-time graph.Open →
- Converting units, and ratesThe standard units of distance and time, converting kilometres per hour to metres per second, minutes to seconds and centimetres to metres, and why units must match in an equation.Open →
- Vectors and scalars in motionThe difference between a scalar and a vector, why distance is a scalar and displacement a vector, how velocity differs from speed, and journeys where the two disagree.Open →
- Distance-time and velocity-time graphsWhat horizontal, sloping and curved lines mean on a distance-time graph, what the gradient and area of a velocity-time graph give, and calculations of acceleration and distance from them.Open →
- Average speed, and the equations of uniform motionHow average speed is found for a changing journey, distance, speed and time calculations, acceleration from a change in velocity, and the equation linking final velocity, starting velocity, acceleration and distance.Open →
- How objects interact, and forces as vectorsThe four ways objects interact and which act at a distance, normal contact force and friction, the equal and opposite pair of forces produced by every interaction, free body force diagrams, and finding the resultant of forces acting along one line.Open →
- Newton's first lawWhat happens to an object with no resultant force on it, what a resultant force can change, and why spacecraft, books, cyclists and sliding loads behave as they do.Open →
- Resolving forces, and free body diagramsResolving a force into two components at right angles, scale drawings and finding the size and direction of a resultant, forces in equilibrium, terminal velocity for a skydiver before and after the parachute opens, and why a car has a top speed that streamlining raises.Open →
- Resultant forces, and balanced forcesFinding the resultant of forces along one line, worked examples for rockets, trolleys, swimmers and lifts, what balanced forces mean, and why a zero resultant does not always mean rest.Open →
- Newton's second law, and inertiaThe relationship between resultant force, mass and acceleration, what one newton means, calculations of force, mass and acceleration, and how inertial mass explains why loaded objects are harder to move.Open →
- Momentum, and force as a change in momentumHow momentum is calculated and its unit, momentum as a vector, conservation of momentum in collisions and when skaters push apart, the force needed to change velocity in a given time, and why crumple zones and padded mats lower the force by lengthening the stopping time.Open →
- Work done, and stored energyHow work done is calculated and its unit, why holding a bag still does no work, where energy goes when work is done against friction, and the energy in a moving object's kinetic store.Open →
- Power, and Newton's third lawThe definition and unit of power with calculations for motors, lamps and stairs, the law describing interaction pairs, and why the two forces of a pair never cancel each other.Open →
- Circular motion and changing velocityWhy an object moving in a circle at steady speed has a changing velocity and is accelerating, the direction of the resultant force, and what supplies it for cars, strings and satellites.Open →
- Stretching, bending and compressing; elastic and plasticThe three ways forces change shape and why at least two forces are needed, the forces that stretch a spring, bend a diving board and compress a pillar, elastic and plastic deformation and how to tell them apart, and why an overstretched spring stays longer.Open →
- Force and extension, linear and non-linearExtension and how to calculate it, direct proportion up to the limit of proportionality, the elastic limit, linear and non-linear force-extension graphs, and the spring-stretching investigation with its variables, precautions, results table, hypothesis, length against force graph and conclusion.Open →
- The spring constant, and work done in stretchingWhat the spring constant measures and its unit, force = spring constant × extension with calculations and stiffness comparisons, work done in stretching as stored energy, work done = ½ × spring constant × extension², the area under a force-extension graph, and the effect of doubling the extension.Open →
- Gravitational fields, weight and free fallGravitational fields around every mass and why they only attract, field strength on the Earth and the Moon, weight as a force measured in newtons with a newtonmeter, how mass differs from weight, the centre of mass, and free fall at about 10 m/s² whatever the mass.Open →
- Calculations with weight and gravitational field strengthThe relationship between weight, mass and gravitational field strength, its rearrangements, worked examples on the Earth and a moon, and how weight and mass behave when the field strength changes.Open →
- Turning forces and the moment of a forceWhat a pivot is and when a force makes an object turn, the direction of rotation, the moment of a force and its unit, calculations of moment, force and perpendicular distance, and the principle of moments applied to balanced see-saws.Open →
- Levers and gearsWhat a lever and a force multiplier are, how a lever, a long spanner and a crowbar multiply force, where the pivot, load and effort sit in a wheelbarrow, and what gears do.Open →
- Pressure in fluids, and the force on a surfaceWhy an inflated balloon holds a rounded shape, why wide snowshoes stop a walker sinking into deep snow and how a hydraulic system multiplies a force.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
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On a distance–time graph, what do a horizontal line, a steeper line and a curve that gets steeper each show?
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State Newton's first law, define a resultant force, and explain why a book stays on a table but a coasting cyclist slows down.
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What is terminal velocity, why does a falling skydiver's acceleration shrink with speed, and what happens once the parachute opens?
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Which instrument would you choose to measure the length of a laboratory bench, and to what precision can it be read?
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What are the standard scientific units of distance and of time?
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How is average speed worked out for a journey in which the speed keeps changing?
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Name four ways in which two objects can interact so that forces act between them.
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How is the resultant of two forces acting along the same straight line found?
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State the relationship between the resultant force on an object, its mass and its acceleration.
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How is the momentum of a moving object calculated?
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How is the work done by a force calculated?
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Define power.
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Since the velocity of an object moving in a circle is changing, what must be acting on it?
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Explain why a single force acting on its own cannot stretch an object.
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What is meant by the extension of a spring?
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What is meant by the spring constant of a spring?
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What surrounds every object that has mass?
Evaluation
Write, in words, the relationship between weight, mass and gravitational field strength.
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What is a pivot?
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What is a lever?
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What is meant by a fluid?
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How could you measure the distance around a running track without laying a rule end to end along it?
Numbers
How is a speed given in kilometres per hour converted into metres per second?
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What is the difference between a scalar quantity and a vector quantity?
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On a distance–time graph, what does a horizontal line show?
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A journey of 150 km takes 3 hours, including a stop. What is the average speed in kilometres per hour?
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Which of the ways objects interact can act without the two objects touching?
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State the law that describes what happens to an object when no resultant force acts on it.
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What does it mean to resolve a force?
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A swimmer whose weight is 600 N experiences an upthrust of 450 N. What is the size and direction of the resultant force on her?
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What is the unit of force, and what does one of it mean in terms of mass and acceleration?
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Is momentum a vector or a scalar quantity?
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What has happened, in terms of energy, when work is done on an object?
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What is the unit of power, and what does one of it mean?
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In which direction does the resultant force act on an object moving round a circular path?
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A spring hangs from a hook with a mass attached to its lower end. Name the two forces that stretch the spring.
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How is the extension of a spring worked out from its stretched and unstretched lengths?
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State the unit of the spring constant.
Evaluation
Compare the gravitational field strength at the surface of the Moon with that at the surface of the Earth, and explain the difference.
Evaluation
How is the mass of an object found from its weight and the gravitational field strength?
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State the unit of the moment of a force.
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What is meant by a force multiplier?
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Explain why an inflated balloon holds a rounded shape.
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How do light gates give a more trustworthy time than a stopwatch pressed by hand?
Take Forces further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Distance vs Displacement
Distance: the total length of the path travelled, with no direction. Displacement: the straight-line separation from start to finish, together with its direction.
Speed vs Velocity
Speed: how fast an object moves, with size only. Velocity: how fast an object moves in a stated direction.
Mass vs Weight
Mass: the quantity of matter in an object, in kilograms, the same everywhere. Weight: the gravitational force on an object, measured in newtons.
Questions from this topic
Each one with the model answer underneath.
- 1
Which instrument would you choose to measure the length of a laboratory bench, and to what precision can it be read?
Model answer
A metre rule or a tape measure, read to the nearest millimetre.
- 2
How could you measure the distance around a running track without laying a rule end to end along it?
Model answer
Use a trundle wheel, which counts complete turns of a wheel of known circumference.
- 3
Why is a hand-operated stopwatch unreliable for timing a very short event?
Model answer
Human reaction time adds an uncertainty of roughly 0.2 s at the start and again at the stop, which is a large fraction of a short interval.
- 4
How do light gates give a more trustworthy time than a stopwatch pressed by hand?
Model answer
The timer starts and stops electronically as the object breaks each beam, so no human reaction time is involved.
- 5
How would you reduce the effect of reaction time when timing a swinging pendulum?
Model answer
Time twenty complete swings and divide the total time by twenty.
- 6
Describe how you would measure the distance travelled by a toy car along a bench and the time it takes, using simple equipment.
Model answer
Mark a start line and a finish line, measure between them with a metre rule, and time the run between the marks with a stopwatch.
What is inside Levo
Six ways to work the same material.
Forces revision questions
- What does Forces cover in OCR GCSE Physics A?
- 22 subtopics: measuring distance and time, and calculating speed, converting units, and rates, vectors and scalars in motion, distance-time and velocity-time graphs, average speed, and the equations of uniform motion, how objects interact, and forces as vectors, newton's first law, resolving forces, and free body diagrams, resultant forces, and balanced forces, newton's second law, and inertia, momentum, and force as a change in momentum, work done, and stored energy, power, and newton's third law, circular motion and changing velocity, stretching, bending and compressing; elastic and plastic, force and extension, linear and non-linear, the spring constant, and work done in stretching, gravitational fields, weight and free fall, calculations with weight and gravitational field strength, turning forces and the moment of a force, levers and gears and pressure in fluids, and the force on a surface. Each one has its own page with questions and model answers.
- How is Forces organised?
- By the OCR J249 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Forces, on a schedule.
Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.
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