Explain why a satellite in a circular orbit around the Earth does not need a continuous thrust force to maintain its orbit.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Gravity provides a centripetal force that pulls the satellite toward the Earth.
The gravitational force continuously changes the direction of the satellite’s velocity, keeping it in a curved path without altering its speed.
The satellite is travelling at the orbital speed that matches the curvature of the Earth’s surface, so it keeps falling toward the Earth while the Earth curves away.
Because there is no air resistance at that altitude, the satellite’s speed is not reduced, so no continuous thrust is required.
The gravitational force continuously changes the direction of the satellite’s velocity, keeping it in a curved path without altering its speed.
The satellite is travelling at the orbital speed that matches the curvature of the Earth’s surface, so it keeps falling toward the Earth while the Earth curves away.
Because there is no air resistance at that altitude, the satellite’s speed is not reduced, so no continuous thrust is required.
Examiner tips
- Mention gravity as the centripetal force. Explain that the force only changes direction, not speed. State the correct orbital speed and the Earth‑curvature idea. Note the absence of air resistance.
Common mistakes
- Confusing centripetal force with thrust. Forgetting to mention that speed remains constant. Including irrelevant details such as atmospheric drag at low Earth orbit.
Mark scheme (4 marks)
- Gravity provides a force on the satellite (towards the Earth / centripetal force)
- This gravitational force continuously changes the direction of the satellite's velocity (without changing its speed)
- The satellite travels at the correct/orbital speed such that the curvature of its path matches the curvature of the Earth's surface / it keeps falling towards Earth but the Earth curves away
- There is no air resistance (in space/at that altitude) to slow the satellite down, so no thrust is needed to maintain speed
Key terms in this question
Related
- All AQA GCSE Physics (8463) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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