Explain orbits with gravity
A satellite’s velocity is continually redirected by gravity. Artificial satellites can be low-orbit, polar or geostationary depending on their purpose and orbital period.
GCSE Physics resources
AQA GCSE Space physics
The Solar System, Satellites and Orbital Motion
A satellite’s velocity is continually redirected by gravity. Artificial satellites can be low-orbit, polar or geostationary depending on their purpose and orbital period.
Start here
The quick revision snapshot
A satellite’s velocity is continually redirected by gravity. Artificial satellites can be low-orbit, polar or geostationary depending on their purpose and orbital period.
By the end, you should be able to…
- Explain explain orbits with gravity using precise physics language.
- Apply the relevant equations, diagrams or practical method to an exam-style situation.
- Use the mini quizzes and practice answers to identify and correct a misconception.
Core learning content
Learn the idea before you practise it
Start with this short teaching sequence for The Solar System, Satellites and Orbital Motion. Read the model, use the visual, then test your recall before moving into examples and exam practice.
Build the picture
Gravity pulls a satellite towards the body it orbits while its sideways velocity carries it forward. The result is continual curved motion. A geostationary satellite has a 24-hour orbit above the equator, so it appears fixed above one point and is useful for communications.
Use the right relationship
Choose a relationship because of the physical change in the question, not because it is familiar. Red-shift idea: red shift = observed wavelength greater than emitted wavelength (qualitative). Orbital model: gravity provides the centripetal force (qualitative). Keep the unit next to each value while you substitute.
What a strong answer does
Name the gravitational force, state the direction of the velocity and explain how the combination produces curved motion. Before writing, underline the command word and identify the information that matters. Keep a calculation as equation, substitution and answer with unit; keep an explanation as a linked chain using because, so or therefore. Finish by checking that the final sentence answers the exact context in the question and that the number, direction or conclusion agrees with the evidence given.
Retrieval practice
Quick checks
Answer without looking back first. The feedback explains the model, so a wrong answer still helps you learn.
Mini quiz 1
Check the core idea
Mini quiz 2
Apply the model
Mini quiz 3
Use exam precision
Try it
Satellite orbit model
How does forward velocity combine with gravity to create an orbit?
What to notice: the readout and written explanation remain available if you do not use the controls.
Worked examples
See the method being built
Cover the answer, attempt the method and then compare your physics language as well as the number.
Example 1 · Why orbit
Explain why a satellite does not fly off in a straight line.
- Identify gravity as resultant force.
- State velocity direction changes.
- Describe continuous curved path.
Show the answer
Gravity continually changes the direction of the satellite’s velocity, producing an orbit.
Example 2 · Geostationary use
Explain why geostationary satellites suit communications.
- State 24 h period and equatorial orbit.
- State appears fixed.
- Link to ground aerial.
Show the answer
It stays above the same point on Earth, so a ground dish can point in one fixed direction.
Example 3 · Low orbit
State one advantage of a low-Earth satellite for imaging.
- Identify shorter distance.
- Link to image detail/latency.
- Avoid claiming it is stationary.
Show the answer
Being closer to Earth can provide higher-resolution images, though it moves relative to the ground.
Misconception clinic
Common wrong turns
Each of these is tempting because it sounds almost right. Replace it with the precise physics before you meet it in a question.
- Saying there is no gravity in orbit.
- Confusing geostationary with any satellite.
- Saying orbital speed is zero.
Independent practice
Exam-style questions
Use the working space first. Reveal the guidance only after you have committed to an answer, then improve the exact part that would gain the next mark.
1. State the force that keeps a satellite in orbit.
[1 mark]Show answer and marking guidance
Gravity.
2. State what a geostationary satellite’s orbital period is.
[1 mark]Show answer and marking guidance
24 hours.
3. State where a geostationary satellite orbits.
[1 mark]Show answer and marking guidance
Above the equator.
4. Explain why a satellite in orbit is accelerating.
[3 marks]Show answer and marking guidance
Its velocity direction is continually changing due to gravity.
5. Give one use of artificial satellites.
[1 mark]Show answer and marking guidance
Communication, weather monitoring, navigation or imaging.
6. Explain why an orbit needs suitable speed.
[3 marks]Show answer and marking guidance
Too slow and it falls lower; too fast and it moves into a larger orbit/escapes depending on conditions.
Questions pupils ask
GCSE Physics FAQs
What is the key idea in The Solar System, Satellites and Orbital Motion?
Space questions reward scale, sequence and evidence. Link observations such as red shift to the model they support, and keep Separate Physics-only content clearly labelled.
How should I practise The Solar System, Satellites and Orbital Motion?
Read the snapshot, attempt the worked examples without looking, complete the mini quizzes and then use the practice questions to check your wording and method.
Next step
Keep your revision moving
Physics sticks when you move between explanation, retrieval and application.