AQA GCSE Physics coverage

Space physics (physics only)

Section 4.8
4 spec leafs

Notes and three levels of exam-style practice for each registered specification leaf in this section.

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4.8.1.1

Our solar system

  • 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.

Tier 1 · Easy

2 marks
ORIGINAL

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

Tier 2 · Standard

4 marks
ORIGINAL

Explain how a cold cloud of gas and dust can develop into a main-sequence star.

Tier 3 · Hard

5 marks
ORIGINAL

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.

4.8.1.2

The life cycle of a star

  • 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.
  • Fusion makes progressively new elements in stars, while elements heavier than iron are made in a supernova; the 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.

Tier 1 · Easy

2 marks
ORIGINAL

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

Tier 2 · Standard

4 marks
ORIGINAL

Describe the stages followed by a star much more massive than the Sun after its main-sequence stage, including both possible remnants.

Tier 3 · Hard

6 marks
ORIGINAL

Explain how stellar processes both create new elements and spread them into the material from which later stars and planets can form.

4.8.1.3

Orbital motion, natural and artificial satellites

  • 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.

Tier 1 · Easy

2 marks
ORIGINAL

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

Tier 2 · Standard

3 marks
ORIGINAL

Compare a planet, one of its moons and a weather satellite by stating one similarity and two distinctions.

Tier 3 · Hard

5 marks
ORIGINAL

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.

4.8.2

Red-shift (physics only)

  • 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.

Tier 1 · Easy

2 marks
ORIGINAL

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.

Tier 2 · Standard

4 marks
ORIGINAL

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.

Tier 3 · Hard

6 marks
ORIGINAL

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.