Space physics
This lesson builds solar system, gravity and orbital motion for GCSE Physics.
Use the core lesson first, then match the exam-board guidance to your school route. Many pupils meet this content through Combined Science as well as Separate Physics.
What you will learn
Exam-board fit
Exact paper labels and specification-point numbering vary by board and cohort, so match this lesson to your school route before using past-paper questions.
Orbit examples supplied on this page
Use planet, moon and satellite examples to practise explaining gravity and orbital motion.
Clear explanation
Space physics is route-specific: some separate Physics courses assess it, while many Combined Science routes do not. The core ideas still build useful force reasoning.
An object in circular orbit is constantly changing direction, so it is accelerating even if its speed is constant. Gravity provides the force towards the centre of the orbit.
Higher stable orbits usually have lower orbital speed and longer orbital period. Satellites stay in orbit because gravity changes their direction rather than simply pulling them straight down.
Key diagram
Worked examples
Why a satellite accelerates at constant speed
A satellite moves around Earth in a circular orbit.
Its speed can stay constant, but its direction keeps changing.
A change in velocity means acceleration.
Quick checks
Choose an answer, then check your thinking.
1. What force keeps a planet in orbit around the Sun?
2. Why is an object in circular orbit accelerating even at constant speed?
Practice questions
Question 1
Name the force that provides centripetal acceleration for the Moon orbiting Earth.
Reveal answer and marking guidance
Answer: Gravity.
Marking: Credit gravitational attraction between Earth and Moon.
Question 2
Why does constant speed not mean zero acceleration in a circular orbit?
Reveal answer and marking guidance
Answer: The direction of velocity changes continuously.
Marking: Credit changing direction in circular motion.
Question 3
State one object in the solar system other than a planet.
Reveal answer and marking guidance
Answer: A moon, asteroid, comet or dwarf planet.
Marking: Credit any valid solar-system object.
Question 4
What generally happens to orbital period for a satellite in a higher orbit?
Reveal answer and marking guidance
Answer: The orbital period is longer.
Marking: Credit longer period at greater orbital radius.
Exam practice ladder
Answers and marking guidance
The exact practice answers are hidden under each question so you can try first. For this lesson, marks come from using the correct physics model, choosing the right equation where needed, keeping units with values, and explaining changes with precise words such as transfer, resultant force, acceleration, evidence and uncertainty.
Common mistakes
- Thinking orbit means no force acts.
- Saying constant speed means no acceleration in circular motion.
- Confusing stars with planets.
- Assuming space physics is on every Combined Science route.
Exam-board guidance
All supported routes assess the core physics idea, but they may group topics, practicals and paper wording differently.
AQA GCSE Physics
AQA GCSE Physics: use this lesson for solar system, gravity and orbital motion, then check whether your class is taking Separate Physics or Combined Science.
OCR GCSE Physics
OCR GCSE Physics: the core physics idea is shared, but Gateway and Twenty First Century may organise questions differently.
Pearson Edexcel GCSE Physics
Pearson Edexcel GCSE Physics: practise the concept, the equation use and the practical language because questions often connect them.
Eduqas GCSE Physics
Eduqas GCSE Physics: learn the core explanation and practise applying it to unfamiliar contexts, data and practical questions.
WJEC Wales
WJEC Wales: check whether your class is using the current GCSE Physics route or a newer science route, then use this lesson for the shared physics idea.
CCEA GCSE Physics
CCEA GCSE Physics: connect the idea to your unit and remember that practical skills are assessed directly.
Extension challenge
Explain why a communications satellite might use a high orbit while an imaging satellite might use a lower orbit.
Reveal answer
Example answer: A strong extension response names the physics model, uses accurate units and explains why the evidence supports the conclusion.
Next lesson
Next, continue with Space Physics: Life Cycle of Stars.