LuduminaSP-02 · SP-U1 · Planned
Gravity and stable orbits
Learning objectives
Describe gravity-maintained planetary/satellite orbits; H explain changing velocity at constant speed and radius change for a different stable speed.
8463 §§4.8.1.3 / No Trilogy counterpart
DfE single-science pp.44–45 · no Combined Space section. Evidence checked 30 September–1 October 2026. Skills: WS1.2,3.6; MS5b.
Explanation
In the circular-orbit approximation, gravity supplies inward force while instantaneous velocity is tangent to the orbit. Higher explanations separate unchanged speed from changing velocity direction and require radius change for a different stable orbital speed in the same system.
Concepts, equations and units: Gravitational force directed inward; circular orbit approximation; H constant speed/changing direction; no centripetal-force/orbital-speed formula requirement.
Prediction, demonstration and game exercise
Predict, observe, explain
Freeze orbit positions and annotate inward force and tangential velocity; H compare two consistent stable orbits.
Planned learner game exercise
Predict motion if inward force removed; H choose model radius consistent with a supplied changed stable speed.
Independent practice
Annotated orbit explanation; H compare radius/speed cases qualitatively using model evidence.
Original practice example · Separate Physics Higher
A satellite moves at constant speed in a circular orbit. Is its velocity constant?
Show working and model answer
Working / reasoning
Its direction changes continuously even when speed stays fixed.
Answer
No; velocity changes direction, requiring inward acceleration/force.
Exit check and success criteria
Force points toward centre, velocity tangent; H changing direction and stable-radius condition correct.
During practice, compare the prediction with evidence and give an error-specific prompt. The exit item uses a fresh context or fresh values, answered independently.
Misconceptions, practical links and mastery
Check these misconceptions
Gravity absent in orbit; inward force points along velocity; any chosen speed remains stable at fixed radius.
Practical preparation
No RP; analytical orbit model required, not Roblox engine default.
Virtual preparation and revision only. Required hands-on activities and school records remain separate.
Proposed mastery
0: not yet evidenced. 1: supported. 2: independent exit criteria met. 3: successful changed-context transfer. Advance at 2; revisit with fresh retrieval. These are not GCSE grades.