4.8 Space physics (physics only) — revision question pack

4 specification points · notes, questions, answers and worked methods

Checked against AQA 8463 section 4.8. Review basis: the qualification registry sourced from the AQA GCSE Physics (8463) specification; registry verification recorded 17 July 2026.

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(physics only) means this content belongs to AQA GCSE Physics (8463), the separate-science qualification, but not AQA Combined Science: Trilogy (8464). It is not an exam tier: (HT only) separately marks Higher-tier content.

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4.8.1.1 · Our solar system

Explanation

The solar system contains the Sun, eight planets and dwarf planets orbiting it, plus natural satellites orbiting planets; it is a small part of the Milky Way galaxy.
A star begins when gravity pulls gas and dust in a nebula together into a protostar; compression raises the temperature until fusion reactions start.
During the stable main-sequence stage, the inward effect of gravitational collapse is in equilibrium with the outward expansion caused by energy from fusion.
A common error is to call the Milky Way the universe or the solar system: the solar system lies within the Milky Way, which is one galaxy in the universe.

Worked example

Place these structures in order from smallest to largest: the Milky Way galaxy, Earth, the solar system.

1.Earth is one planet in the solar system, and the whole solar system is only a small part of the Milky Way. Therefore the size order is Earth, solar system, Milky Way.

Answer: Earth, solar system, Milky Way galaxy.

Common mistakes

Don't call the Milky Way the universe or the solar system: the solar system lies within the Milky Way, which is one galaxy in the universe.
Don't fall into the trap of calling a moon a planet or placing planets in the wrong order from the Sun.

Exam tip

Describe the Solar System as the Sun, eight planets and their moons plus smaller orbiting bodies.

Tier 1 · Easy

Explain how a cloud of gas and dust can become hot enough for fusion to begin in a protostar.
[2 marks]
Total for this question: 2
Choose the correct statement and explain your choice: A, the Milky Way is inside the solar system; B, the solar system is a small part of the Milky Way; C, the Milky Way and the solar system are the same object.
[2 marks]
Total for this question: 2

Tier 2 · Standard

Explain how a cold cloud of gas and dust can develop into a main-sequence star.
[4 marks]
Total for this question: 4
Light takes about 8 minutes to travel from the Sun to Earth, about 4.2 years from the nearest other star to Earth, and about 100 000 years to cross the Milky Way. Use the data to rank Earth, the solar system and the Milky Way from smallest scale to largest, and justify the placement of the solar system.
[3 marks]
Total for this question: 3
A catalogue groups the Sun, the eight planets, natural satellites and several distant stars as members of the solar system. Identify the incorrectly grouped objects and explain how the solar system fits within the Milky Way.
[3 marks]
Total for this question: 3

Tier 3 · Hard

A young star stops contracting rapidly after sustained fusion begins. Explain the equilibrium that makes the star stable and predict what happens if its fusion output temporarily decreases.
[5 marks]
Total for this question: 5
Object X is a contracting cloud with a rising central temperature but no sustained fusion. Object Y has sustained fusion and an approximately constant size. One astronomer labels X a main-sequence star and Y a protostar. Evaluate both labels and use the observations to explain the correct stages.
[5 marks]
Total for this question: 5
A model of star formation states: ‘Gravity spreads a cloud of gas and dust out. Compression then lowers its temperature. When fusion begins, gravity stops acting and the outward effect of fusion alone keeps the star stable.’ Identify and correct the errors in this model.
[4 marks]
Total for this question: 4
A telescope observes star T in the Milky Way, planet P orbiting T, and moon M orbiting P. A researcher states that P and M are members of our solar system because all three objects are in the Milky Way. Evaluate the statement by explaining the three nested systems and what would have to be true for P and M to belong to our solar system.
[5 marks]
Total for this question: 5
Object X is contracting, becoming hotter and has no sustained fusion. Object Y has sustained fusion and keeps an approximately constant radius. Identify the stage of each object and explain why gravity produces continued contraction in X but not in Y.
[5 marks]
Total for this question: 5

4.8.1.2 · The life cycle of a star

Explanation

All stars follow nebula $\rightarrow$ protostar $\rightarrow$ main-sequence star; their later path is determined by the star's mass.
A Sun-sized star becomes a red giant, then a white dwarf and finally a black dwarf; a much more massive star becomes a red supergiant, then a supernova, leaving a neutron star or black hole.
Successive fusion reactions in stars produce elements up to iron; elements heavier than iron are made in a supernova, whose explosion distributes elements through the universe.
A common error is to give one ending for every star: only the much-more-massive route includes a supernova and can leave a neutron star or black hole.

A star's life cycle branches after the main sequence according to its mass.

Worked example

Complete the late-life sequence for a star about the size of the Sun: red giant → ______ → ______.

1.Follow the Sun-sized branch of the life-cycle diagram: after red giant comes white dwarf, which cools to become a black dwarf.

Answer: White dwarf, then black dwarf.

Common mistakes

Don't give one ending for every star: only the much-more-massive route includes a supernova and can leave a neutron star or black hole.
Don't fall into the trap of saying every star ends as a black hole regardless of its mass.

Exam tip

State the initial mass branch before giving the final stages of a star's life cycle.

Tier 1 · Easy

State where elements up to iron are produced and where elements heavier than iron are produced.
[2 marks]
Total for this question: 2
Observations show a very massive star becoming a red supergiant and later leaving a neutron star. Name the explosive stage missing between these observations.
[2 marks]
Total for this question: 2

Tier 2 · Standard

Describe the stages followed by a star much more massive than the Sun after its main-sequence stage, including both possible remnants.
[4 marks]
Total for this question: 4
A meteorite contains iron and gold. Identify the stellar process associated with producing the iron, identify where the gold was produced, and explain how both could later become part of the meteorite.
[4 marks]
Total for this question: 4
An old star that began with about the same mass as the Sun is now a white dwarf. An astronomer predicts that it will next explode as a supernova and become a black hole. Correct the prediction by identifying the stage before the white dwarf and its expected final stage.
[4 marks]
Total for this question: 4

Tier 3 · Hard

Explain how stellar processes both create new elements and spread them into the material from which later stars and planets can form.
[6 marks]
Total for this question: 6
Records for star P show a Sun-like initial mass, then red giant and white dwarf stages. Records for star Q show a much greater initial mass, then red supergiant, supernova and neutron-star stages. A researcher claims that initial mass does not affect a star's later life and that both stars make elements heavier than iron during ordinary fusion. Evaluate the claim using all the records.
[6 marks]
Total for this question: 6
A young planetary system contains iron, elements lighter than iron and an element heavier than iron. A researcher claims that every one of these elements must have been made in the same supernova. Evaluate what the composition does and does not show about the material's stellar history.
[5 marks]
Total for this question: 5
A life-cycle model predicts that star A will end as a black dwarf and star B will leave a neutron star. For each star, give the sequence from the main-sequence stage to the stated remnant and explain what the different remnants show about the stars' initial masses.
[6 marks]
Total for this question: 6
Gold is present in the Sun. A researcher concludes that the Sun must therefore produce gold during ordinary fusion and will later explode as a supernova. Evaluate both parts of the conclusion and explain how gold could have entered the material from which the Sun formed.
[5 marks]
Total for this question: 5

4.8.1.3 · Orbital motion, natural and artificial satellites

Explanation

Gravity supplies the inward force that keeps planets, natural satellites and artificial satellites in circular orbits.
Classify by what is orbited and origin: planets orbit the Sun, natural satellites are moons orbiting planets, and artificial satellites are human-made objects placed in orbit.
Higher only: in a circular orbit gravity changes velocity direction while speed can stay constant; if speed changes in a stable orbit, the orbital radius must also change.
A common error is to say orbiting objects have no force acting on them; without the inward gravitational force they would not follow a circular path.

Worked example

Name the force that maintains the Moon's orbit around Earth and state whether the Moon is a natural or artificial satellite.

1.An orbit requires an inward gravitational force. The Moon was not placed in orbit by humans, so it is classified as a natural satellite.

Answer: Gravity maintains the orbit. The Moon is a natural satellite.

Common mistakes

Don't say orbiting objects have no force acting on them; without the inward gravitational force they would not follow a circular path.
Don't fall into the trap of saying an orbiting satellite has no resultant force because its speed is constant.

Exam tip

For orbit questions, link gravity to centripetal acceleration and continuous direction change.

Tier 1 · Easy

Compare Earth with a weather satellite by stating what each orbits, and name the force that keeps each in orbit.
[3 marks]
Total for this question: 3
Object P formed naturally and orbits Jupiter. Object Q was built by humans and placed in orbit around Earth. Classify each object as a natural or artificial satellite.
[2 marks]
Total for this question: 2

Tier 2 · Standard

Compare a planet, one of its moons and a weather satellite by stating one similarity and two distinctions.
[3 marks]
Total for this question: 3
An astronaut says that gravity has stopped acting on an orbiting spacecraft because the craft does not fall straight down to Earth. Use the shape of its path to explain why this conclusion is wrong.
[3 marks]
Total for this question: 3
A diagram of a satellite in a circular orbit around Earth shows one arrow labelled ‘force from Earth’ drawn in the same direction as the satellite's motion. Give what is wrong with the arrow, state the correct direction for it, and explain what path the satellite would follow if that force were removed.
[4 marks]
Total for this question: 4

Tier 3 · Hard

Higher only: a satellite travels at constant speed in a stable circular orbit. Explain how gravity changes its velocity without changing its speed, and state what must happen to the orbital radius if the speed changes but the orbit remains stable.
[5 marks]
Total for this question: 5
Higher only: satellite A maintains a fixed speed while following a circular path of radius $7.0\times10^3\,\text{km}$ . Satellite B is stable at radius $2.8\times10^4\,\text{km}$ and has a lower speed. An engineer claims that each satellite has constant velocity and that speed can change without any change of stable-orbit radius. Critique both parts of the claim using the observations and gravity.
[5 marks]
Total for this question: 5
Higher only: a satellite travels clockwise around centre O in a circular orbit. At three instants it is directly north, east and south of O. State its instantaneous velocity direction at each position, state the direction of gravity at the east position, and explain how these directions show acceleration at constant speed.
[5 marks]
Total for this question: 5
Higher only: three artificial satellites are in stable circular orbits around the same planet. Their radii are $7.0$ , $14$ and $28$ thousand kilometres, and their speeds are $7.5$ , $5.3$ and $7.2\,\text{km/s}$ respectively. Identify the result that conflicts with the speed-radius relationship, state the expected comparison, and explain why a satellite's velocity changes even while its speed is constant.
[4 marks]
Total for this question: 4

4.8.2 · Red-shift (physics only)

Explanation

Light from most distant galaxies is observed at longer wavelengths than expected; this red-shift is the qualitative signature of galaxies receding from us.
Compare spectral lines with laboratory wavelengths: a shift towards longer wavelengths indicates recession, and a larger shift indicates a greater recession speed.
More distant galaxies generally recede faster and show greater red-shift, providing evidence that the universe is expanding and supporting a hot, dense beginning in the Big Bang model.
A common error is to present the Big Bang as unchangeable fact: scientific theories are built from observations and may be refined as new evidence appears; dark mass and dark energy remain incompletely understood.

Worked example

A spectral line from a galaxy is observed at a longer wavelength than the same line measured in a laboratory. Name this effect and state what it indicates about the galaxy.

1.A shift of known spectral lines towards longer wavelengths is red-shift. In this context, red-shift indicates motion away from the observer.

Answer: The effect is red-shift. It indicates that the galaxy is receding.

Common mistakes

Don't present the Big Bang as unchangeable fact: scientific theories are built from observations and may be refined as new evidence appears; dark mass and dark energy remain incompletely understood.
Don't fall into the trap of interpreting red-shift as a star literally becoming red rather than a wavelength change.

Exam tip

For red-shift evidence, connect longer observed wavelengths to recession and expansion of the Universe.

Tier 1 · Easy

Explain why the Big Bang model is described as a scientific theory rather than an unchangeable fact.
[2 marks]
Total for this question: 2
A spectral line measured at $656\,\text{nm}$ in a laboratory is observed at $660\,\text{nm}$ in light from a distant galaxy. Name the effect and state what it indicates about the galaxy's motion.
[2 marks]
Total for this question: 2

Tier 2 · Standard

Galaxy R is farther away than galaxy S and its spectral lines show a larger red-shift. Explain the conclusions astronomers draw from these observations.
[4 marks]
Total for this question: 4
The same laboratory spectral line is at $500\,\text{nm}$ . Galaxy P, $200$ million light-years away, shows it at $502\,\text{nm}$ ; Q, $500$ million light-years away, at $507\,\text{nm}$ ; and R, $900$ million light-years away, at $512\,\text{nm}$ . Rank their recession speeds and state one conclusion the data support and one quantity the data do not determine.
[4 marks]
Total for this question: 4
Three spectral lines occur at $400\,\text{nm}$ , $500\,\text{nm}$ and $600\,\text{nm}$ in a laboratory. A galaxy spectrum contains the corresponding pattern at $404\,\text{nm}$ , $505\,\text{nm}$ and $606\,\text{nm}$ . Explain how the pattern helps identify the lines and state the conclusion about the galaxy's motion.
[3 marks]
Total for this question: 3

Tier 3 · Hard

New supernova observations suggest that very distant galaxies are receding ever faster. Explain how scientists use such observations when evaluating the Big Bang model, and why unresolved dark mass and dark energy do not make the model unscientific.
[6 marks]
Total for this question: 6
For one reference line, galaxies at distances $100$ , $300$ , $600$ and $900$ million light-years have observed wavelengths $657\,\text{nm}$ , $660\,\text{nm}$ , $666\,\text{nm}$ and $664\,\text{nm}$ respectively; the laboratory wavelength is $656\,\text{nm}$ . A scientist says every more distant galaxy in this sample has a larger red-shift and that the table proves the Big Bang model can never be revised. Evaluate both statements and give the strongest conclusion supported by the data.
[6 marks]
Total for this question: 6
One nearby galaxy has spectral lines at shorter wavelengths than the laboratory values. A survey of many distant galaxies shows longer wavelengths, with the largest increases for the most distant galaxies. Explain what each result shows about those galaxies' motion, and explain why the survey rather than the single nearby galaxy is used as evidence that the universe is expanding.
[5 marks]
Total for this question: 5
Raisins are distributed throughout rising dough. As the dough expands, every raisin sees the others move away, and more distant raisins separate faster. Explain two ways this model represents observations of galaxies, give one limitation of the model, and link the observations to the Big Bang model.
[5 marks]
Total for this question: 5
Red-shift measurements give recession speeds of $240$ , $480$ and $720\,\text{km/s}$ for galaxies at relative distances $1.0$ , $2.0$ and $3.0$ . Calculate the recession-speed-to-distance ratio for each galaxy. Explain what the common ratio suggests about expansion and how extrapolating the pattern backwards supports the Big Bang model.
[5 marks]
Total for this question: 5

Answer key

Answers begin on a new printed page so the question pack can be completed without the solutions alongside it.

4.8.1.1 · Our solar system

Tier 1 · Easy

Mark scheme for 4.8.1.1 Tier 1 · Easy
Question	Answers	Extra information	Mark
01.1	Gravity pulls the gas and dust together. Compression raises the temperature until fusion reactions can start.	Follow the effect of gravitational collapse. As the material is pulled into a smaller region it is compressed and heats up; fusion begins once the protostar becomes hot enough.	2
Total Question 1			2
02.1	Statement B is correct. The solar system contains the Sun and objects orbiting it, whereas the Milky Way is the galaxy containing the solar system and many other stars.	Use the nesting of astronomical structures. The Sun's orbiting system is only one small system among the many stars and systems in the Milky Way galaxy.	2
Total Question 2			2

Tier 2 · Standard

Mark scheme for 4.8.1.1 Tier 2 · Standard
Question	Answers	Extra information	Mark
01.1	Gravity pulls the gas and dust together. The contracting material forms a protostar and becomes hotter. At a sufficiently high temperature, nuclei begin to fuse. The star enters a stable main-sequence stage when fusion is established.	Link the stages causally: gravitational attraction causes collapse and compression, compression raises temperature, and a high enough core temperature allows nuclear fusion to begin.	4
Total Question 1			4
02.1	The order is Earth, solar system, Milky Way. The Sun-to-Earth journey is within the solar system and is far shorter than the journey from another star. The very long crossing time for the Milky Way shows that the solar system occupies only a small part of the galaxy.	Because all three times refer to light, compare the times as distance evidence. The within-system time is smallest, the interstellar time is much greater, and the galactic crossing time is greatest.	3
Total Question 2			3
03.1	The several distant stars are incorrectly grouped as members of the solar system. The solar system consists of the Sun and the objects that orbit it, including planets, dwarf planets and smaller bodies; natural satellites orbit planets within it. The solar system is only a small part of the Milky Way, which contains many other stars.	Classify objects by their orbital system before placing that system in the larger structure. The Sun and its orbiting bodies form the solar system; other stars can belong to the Milky Way without belonging to the solar system.	3
Total Question 3			3

Tier 3 · Hard

Mark scheme for 4.8.1.1 Tier 3 · Hard
Question	Answers	Extra information	Mark
01.1	Gravity acts inward and tends to collapse the star. Energy released by fusion produces an outward expansion effect or pressure. In a stable star, the inward and outward effects are balanced. If fusion output decreases, the outward effect becomes smaller than gravity. The star begins to contract until a new balance can be established.	Identify the two opposing effects, then compare them. Equal inward gravity and outward fusion-driven expansion give equilibrium; reducing only the outward effect leaves a resultant inward effect and causes contraction.	5
Total Question 1			5
02.1	X is a protostar, not a main-sequence star. Gravity is pulling its gas and dust together, causing compression and a temperature rise. Its lack of sustained fusion shows that it has not reached the main-sequence stage. Y is a main-sequence star because sustained fusion has begun. Its approximately constant size is evidence of equilibrium between inward gravitational collapse and the outward expansion effect caused by fusion energy.	Give priority to the diagnostic evidence rather than temperature alone. Contraction without sustained fusion identifies a protostar; established fusion plus stable size identifies the balanced main-sequence stage.	5
Total Question 2			5
03.1	Gravity pulls the gas and dust together rather than spreading it out. The contracting material is compressed, and compression raises its temperature rather than lowering it. Gravity continues to act inward after fusion starts. A main-sequence star is stable because the inward effect of gravity is in equilibrium with the outward expansion effect caused by fusion energy.	Audit the model in causal order: gravitational collapse, compression and heating, then main-sequence equilibrium. Stability requires two continuing opposing effects, not the disappearance of gravity.	4
Total Question 3			4
04.1	The Milky Way is a galaxy containing many stars, including the Sun and star T. Planet P and moon M can be in the Milky Way without being in our solar system. P belongs to the planetary system around star T because it orbits T. M belongs to that system because it orbits P. For P and M to belong to our solar system, P would need to orbit the Sun and M would need to orbit an object within the Sun's system.	Membership depends on the body orbited, not merely on sharing a galaxy. Build the nesting from moon to planet to star system, then place that whole system inside the Milky Way.	5
Total Question 4			5
05.1	X is a protostar. Gravity pulls its gas and dust together, causing contraction and compression. Compression raises its temperature, but sustained fusion has not yet begun to provide the outward effect needed for stability. Y is a main-sequence star because it has sustained fusion and a stable size. In Y, the inward effect of gravity is in equilibrium with the outward expansion effect caused by energy from fusion.	Use fusion as the stage discriminator. Gravity acts in both objects, but only the main-sequence star has a fusion-driven outward effect that balances the inward collapse.	5
Total Question 5			5

4.8.1.2 · The life cycle of a star

Tier 1 · Easy

Mark scheme for 4.8.1.2 Tier 1 · Easy
Question	Answers	Extra information	Mark
01.1	Fusion reactions in stars produce elements up to iron. Elements heavier than iron are produced in a supernova.	Separate ordinary stellar fusion from the explosive stage. Successive fusion reactions build nuclei up to iron; the conditions in a supernova produce heavier elements.	2
Total Question 1			2
02.1	The missing stage is a supernova. A red supergiant explodes before the remaining core can become a neutron star.	Follow the high-mass branch of the stellar life cycle: red supergiant, then supernova, then a neutron star or black hole remnant.	2
Total Question 2			2

Tier 2 · Standard

Mark scheme for 4.8.1.2 Tier 2 · Standard
Question	Answers	Extra information	Mark
01.1	It expands into a red supergiant. It explodes as a supernova. The remnant becomes either a neutron star or a black hole.	Select the high-mass branch rather than the Sun-sized branch. Preserve the order red supergiant, supernova, then give the two alternative remnants: neutron star or black hole.	4
Total Question 1			4
02.1	Iron can be produced by successive fusion reactions in stars. Gold, which is heavier than iron, is produced in a supernova. A supernova ejects and distributes elements through the universe. The dispersed material can enter a later cloud of gas and dust from which a planetary system and meteorites form.	Separate element production at the iron boundary from later distribution. Stellar fusion reaches iron; a supernova produces heavier elements and spreads material that can be incorporated into later objects.	4
Total Question 2			4
03.1	Before becoming a white dwarf, the Sun-sized star was a red giant. The white dwarf is expected to cool and become a black dwarf. It is not expected to undergo a supernova. The supernova and black-hole route is for a star initially much more massive than the Sun.	Use the stated initial mass to select one branch. A Sun-sized star follows red giant, white dwarf, black dwarf; do not splice in stages from the much-more-massive branch.	4
Total Question 3			4

Tier 3 · Hard

Mark scheme for 4.8.1.2 Tier 3 · Hard
Question	Answers	Extra information	Mark
01.1	Fusion joins lighter nuclei to make heavier nuclei during a star's life. Successive fusion processes produce naturally occurring elements up to iron. A massive star later undergoes a supernova explosion. Elements heavier than iron are produced in the supernova. The explosion ejects and distributes elements through the universe. The dispersed material can become part of later clouds of gas and dust from which stars and planets form.	Separate creation from distribution. Fusion within stars builds new nuclei; the supernova stage both produces nuclei heavier than iron and ejects material, enriching later nebulae.	6
Total Question 1			6
02.1	The different records show that the later life cycle depends on initial mass. The Sun-like star follows the red-giant and white-dwarf route. The much more massive star follows the red-supergiant and supernova route. A neutron star is a possible remnant of that supernova. Successive fusion reactions in stars produce elements only up to iron. Elements heavier than iron are produced in a supernova, so the researcher's second statement is also incorrect.	Use P and Q as contrasting evidence for mass-dependent branches, then apply the specification's production boundary: ordinary stellar fusion reaches iron, while the supernova stage produces heavier elements.	6
Total Question 2			6
03.1	The element heavier than iron provides evidence that material from a supernova is present. Successive fusion reactions in stars can produce elements up to iron, including the iron and lighter elements. A supernova can eject and distribute both newly produced heavy elements and material made earlier in the star. The composition alone does not show that all the elements were produced during one explosion or by one star. The distributed material later became part of the gas and dust from which the young planetary system formed.	Separate production from distribution and keep the conclusion within the evidence. A heavier-than-iron element requires supernova production, but the same debris can also carry earlier fusion products, so common location does not prove common production time.	5
Total Question 3			5
04.1	A followed main-sequence star, red giant, white dwarf, then black dwarf. A therefore began with about the same mass as the Sun rather than being much more massive. B followed main-sequence star, red supergiant, supernova, then neutron star. B therefore began much more massive than the Sun. The neutron star is a remnant left after the massive-star supernova. The contrasting sequences show that a star's later life cycle depends on its initial mass.	Reason backwards from each remnant to choose the correct branch, then write that branch forwards from the main sequence. The branch difference supplies the initial-mass conclusion.	6
Total Question 4			6
05.1	Ordinary fusion in stars produces elements only up to iron, so it does not produce gold, which is heavier than iron. Elements heavier than iron are produced in a supernova. A previous supernova could have ejected and distributed gold through the universe. That gold could then have become part of the cloud of gas and dust from which the Sun formed. The Sun is not expected to explode as a supernova; a Sun-sized star follows the red-giant, white-dwarf and black-dwarf route.	Separate an element's earlier origin from the future of the star that now contains it. Supernova debris can be recycled into a later Sun-sized star without putting that later star on the massive-star branch.	5
Total Question 5			5

4.8.1.3 · Orbital motion, natural and artificial satellites

Tier 1 · Easy

Mark scheme for 4.8.1.3 Tier 1 · Easy
Question	Answers	Extra information	Mark
01.1	Earth orbits the Sun; the weather satellite orbits Earth. Both are kept in orbit by the gravitational force. That force acts towards the centre of the orbit, continuously changing the direction of motion.	Identify what each object orbits, then the force responsible. Gravity provides the inward force in both cases, acting towards the orbited body and changing the direction of travel rather than the speed.	3
Total Question 1			3
02.1	P is a natural satellite, or moon, of Jupiter. Q is an artificial satellite of Earth.	Classify by origin rather than by the planet orbited. A naturally formed orbiting body is a natural satellite; a human-made orbiting object is artificial.	2
Total Question 2			2

Tier 2 · Standard

Mark scheme for 4.8.1.3 Tier 2 · Standard
Question	Answers	Extra information	Mark
01.1	All three are kept in orbit by gravity. A planet orbits the Sun, whereas the moon and weather satellite orbit a planet. The moon is natural, whereas the weather satellite is artificial and human-made.	Use gravity as the shared feature. Then distinguish the central body orbited and distinguish natural origin from deliberate human placement.	3
Total Question 1			3
02.1	Gravity still acts on the spacecraft towards Earth or the centre of its orbit. The inward gravitational force continually bends the spacecraft's path. Without gravity it would not follow the curved orbit; it would continue in a straight line.	Treat the curved path as evidence of a force. Gravity continually pulls the moving craft inward, so it falls around Earth rather than travelling straight ahead.	3
Total Question 2			3
03.1	The force arrow must not point in the same direction as the satellite's motion. It should point towards the centre of the orbit, towards Earth. Gravity from Earth provides this inward force. If the force were removed, the satellite would travel in a straight line.	Compare the tangential direction of motion with the radial direction of the force. Earth's gravity acts towards the centre and bends the path; without that inward force, the satellite continues along a straight-line path.	4
Total Question 3			4

Tier 3 · Hard

Mark scheme for 4.8.1.3 Tier 3 · Hard
Question	Answers	Extra information	Mark
01.1	Gravity supplies a force towards the centre of the orbit. This inward force continually changes the direction of motion. Velocity changes because velocity includes direction, even though speed stays constant. The satellite is therefore accelerating towards the centre. If its speed changes in a stable orbit, its orbital radius must also change.	Separate speed from velocity: an unchanged speed can accompany a continuously changing direction. Gravity provides that directional change, and the stable-orbit condition links any speed change to a change in radius.	5
Total Question 1			5
02.1	Each satellite's velocity changes because its direction changes continuously, even when its speed is constant. Gravity supplies the inward force that changes this direction. Each satellite is therefore accelerating towards the centre of its orbit. The observations link the different stable radii with different speeds. For a satellite to remain in a stable orbit after its speed changes, its orbital radius must also change, so the engineer's second claim is incorrect.	Separate speed from velocity, then use the two stable-orbit observations. Circular motion changes velocity direction through gravity, and the specification links a stable speed change to a radius change.	5
Total Question 2			5
03.1	At the north position, the instantaneous velocity is towards the east. At the east position, the instantaneous velocity is towards the south. At the south position, the instantaneous velocity is towards the west. At the east position, gravity acts westwards towards O. Gravity continually changes the direction of velocity, so velocity changes and the satellite accelerates even if the speed is constant.	For clockwise motion, draw a tangent at each named position to obtain the velocity direction. Gravity is radial and inward, perpendicular to the instantaneous motion, so it changes direction rather than requiring a speed change.	5
Total Question 3			5
04.1	The $7.2\,\text{km/s}$ speed at radius $28$ thousand kilometres conflicts with the relationship. A stable orbit with the larger radius should have a lower speed than the $5.3\,\text{km/s}$ satellite at radius $14$ thousand kilometres. Gravity acts towards the centre of each orbit, continually changing the direction of motion. Velocity changes because it includes direction, even though the speed remains constant.	Test the ordered data against the qualitative stable-orbit relationship: larger radius goes with lower speed. Then treat constant speed and changing velocity as compatible because gravity changes direction continuously.	4
Total Question 4			4

4.8.2 · Red-shift (physics only)

Tier 1 · Easy

Mark scheme for 4.8.2 Tier 1 · Easy
Question	Answers	Extra information	Mark
01.1	The model is supported by observations, including red-shift evidence for an expanding universe. Scientific theories can be refined or replaced if new evidence provides a better explanation — and much about the Universe is still not understood, dark mass and dark energy being the specification's own examples.	Link the model to evidence, then state how science responds to new observations. Evidence makes the model scientific, while continued testing, and the parts of the Universe still not explained, mean it is not treated as permanently fixed.	2
Total Question 1			2
02.1	The wavelength has undergone red-shift because the observed value is longer. The red-shift indicates that the galaxy is moving away from the observer.	Compare the same line at source and in the galaxy spectrum. A shift from $656\,\text{nm}$ to the longer wavelength $660\,\text{nm}$ is a red-shift and is evidence of recession.	2
Total Question 2			2

Tier 2 · Standard

Mark scheme for 4.8.2 Tier 2 · Standard
Question	Answers	Extra information	Mark
01.1	Both galaxies are receding because their light is red-shifted. R is receding faster because it has the larger red-shift. The pattern that more distant galaxies recede faster is evidence that the universe is expanding. This expansion evidence supports the Big Bang model.	Translate red-shift into recession, compare shift size to compare speeds, then connect the speed-with-distance trend to an expanding universe and the Big Bang model.	4
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02.1	The recession-speed order from lowest to highest is P, Q, R. R has the largest red-shift and P the smallest. The greater shifts for more distant galaxies support the conclusion that the universe is expanding. These data alone do not determine the age of the universe.	Subtracting the common $500\,\text{nm}$ reference gives shifts of $2\,\text{nm}$ , $7\,\text{nm}$ and $12\,\text{nm}$ . Rank recession speed by shift size, then keep the conclusion limited to what the distance-shift pattern supports.	4
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03.1	Each galaxy wavelength is $1.01$ times its corresponding laboratory wavelength, so the shared relative pattern identifies the same set of spectral lines. Every corresponding line is shifted towards a longer wavelength, so the spectrum is red-shifted. The red-shift indicates that the galaxy is receding from the observer.	Match the group of lines rather than relying on one feature. The preserved pattern supports the correspondence, and the common displacement to longer wavelengths identifies red-shift and recession.	3
Total Question 3			3

Tier 3 · Hard

Mark scheme for 4.8.2 Tier 3 · Hard
Question	Answers	Extra information	Mark
01.1	Scientists compare predictions or implications of a model with repeatable astronomical observations. Red-shift and the recession-speed trend provide evidence that the universe is expanding. Expansion from an earlier state supports the Big Bang model of an initially very hot, dense, small region. The newer supernova observations can refine the model by indicating accelerating recession. Scientific theories remain open to revision when further evidence is collected. Unexplained dark mass and dark energy identify limits of present understanding rather than removing the existing observational evidence.	Treat the model as an evidence-based explanation, not a final certainty. Link red-shift to expansion and hence to the Big Bang, then explain that new acceleration evidence and unresolved phenomena motivate refinement and further testing.	6
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02.1	All four wavelengths exceed $656\,\text{nm}$ , so all four galaxies are red-shifted and receding. The shifts are $1\,\text{nm}$ , $4\,\text{nm}$ , $10\,\text{nm}$ and $8\,\text{nm}$ . The $900$ million light-year galaxy has a smaller shift than the $600$ million light-year galaxy, so the word ‘every’ is contradicted by the table. The overall pattern still tends towards greater red-shift at greater distance. That trend supports an expanding universe and therefore supports the Big Bang model. It does not make the model unchangeable; scientific explanations can be refined when new or better evidence is obtained.	Compare each observed wavelength with the common laboratory value before judging the claim. One local reversal defeats the universal statement, while the broader upward trend remains evidence for expansion rather than final proof of an unrevisable model.	6
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03.1	The nearby galaxy's shorter wavelengths show that it is moving towards us. The distant galaxies are red-shifted, so they are receding from us. A larger red-shift indicates a greater recession speed. The survey shows that greater distance goes with faster recession. One nearby galaxy cannot establish a distance–speed trend, whereas the survey can provide evidence of that general pattern and therefore of expansion.	Compare each observed wavelength with its laboratory value, then use shift size to compare recession speeds. Evidence for expansion comes from the distance–speed pattern across many galaxies, not the motion of one nearby galaxy.	5
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04.1	The separating raisins represent galaxies receding as the universe expands. The faster separation of more distant raisins represents the observation that more distant galaxies generally recede faster. Every raisin observing recession represents expansion without making our galaxy a unique central position. One limitation is that the dough has an edge or expands into surrounding space, so it is not a complete representation of the universe. The expansion pattern supports the model that the universe expanded from an initially very small, hot and dense region.	Map each stated feature of the model to one observation before stating a physical limitation. Use the shared recession pattern as evidence for expansion and hence for the Big Bang model.	5
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05.1	The ratios are $240/1.0=240$ , $480/2.0=240$ and $720/3.0=240$ in the stated relative units. The common ratio shows that recession speed is directly proportional to distance for these data. The greater recession speeds of more distant galaxies support an expanding universe. Extrapolating the expansion backwards suggests that the universe began in a much smaller region. This supports the Big Bang model of an initially very hot and dense universe.	Calculate all three ratios before judging the relationship. Use the present expansion trend in reverse as evidence supporting a much smaller, hot and dense beginning.	5
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