AQA GCSE Physics 4.8.1 Solar System, Stability of Orbital Motions and Satellites Exam Questions

About AQA GCSE Physics 4.8.1 Solar System, Stability of Orbital Motions and Satellites

Space physics is a physics only topic in AQA GCSE Physics, examined on Paper 2. This section covers our solar system and galaxy, how the Sun formed from a nebula, the life cycle of stars of different masses, how elements are produced by fusion and supernovae, and the orbits of planets, moons and artificial satellites. Higher tier only content explains how an object in a circular orbit has a changing velocity but constant speed, and how speed changes with orbit radius. Examiners test life cycle sequences, the balance of forces in a main sequence star and orbit explanations.

What you need to know

• Our solar system Within our solar system there is one star, the Sun, plus the eight planets and the dwarf planets that orbit around the Sun. Natural satellites, the moons, orbit planets. Our solar system is a small part of the Milky Way galaxy.
• Formation of the Sun The Sun was formed from a cloud of dust and gas (nebula) pulled together by gravitational attraction. As it collapsed it heated up until fusion began, forming a protostar and then a star.
• Main sequence stability A star is stable during the main sequence because the inward force of gravity is balanced by the outward pressure from fusion energy in the core.
• Life cycle of stars A star about the size of the Sun: main sequence, red giant, white dwarf, black dwarf. A star much more massive than the Sun: main sequence, red super giant, supernova, then a neutron star or a black hole.
• Formation of elements Fusion processes in stars produce all of the naturally occurring elements up to iron. Elements heavier than iron are produced in a supernova. The explosion of a massive star distributes the elements throughout the universe.
• Orbits Gravity provides the force that allows planets and satellites (both natural and artificial) to maintain their circular orbits.
• Orbital motion (Higher tier only) For circular orbits the force of gravity can lead to a changing velocity but unchanged speed. For a stable orbit, the radius must change if the speed changes: a smaller orbit requires a higher speed.

Common mistakes in 4.8.1 Solar System, Stability of Orbital Motions and Satellites

• Saying the Sun is in the main sequence because there is no gravity. Gravity is balanced by outward pressure from fusion.
• Getting the life cycle order wrong, or giving a Sun-sized star a supernova. Only stars much more massive than the Sun become supernovae.
• Saying elements heavier than iron form in main sequence stars. They are formed in supernovae.
• Saying satellites in circular orbit have no resultant force. Gravity is a resultant force towards the centre that changes the direction of velocity.
• Saying a satellite in a lower orbit moves more slowly. Closer orbits need a higher speed.

Try three 4.8.1 Solar System, Stability of Orbital Motions and Satellites exam-style questions