This higher tier covers Higher Tier Only: System Boundaries and Energy Accounting within Energy Stores & Systems for GCSE Physics. Revise Energy Stores & Systems in Energy for GCSE Physics with 14 exam-style questions and 30 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 17 of 20 in this topic. This section is most useful once the core foundation idea is secure, because it adds the detail that pushes answers higher.
🎓 Higher Tier Only: System Boundaries and Energy Accounting
At higher tier, you need to define system boundaries carefully. When a ball is dropped, if we define the system as "the ball only", then gravity does work on the ball, increasing its kinetic energy — energy enters the system via mechanical work.
If we define the system as "ball + Earth", then the GPE of the ball-Earth system converts to KE of the ball. No energy crosses the system boundary. This is a closed system in the absence of air resistance.
In reality, air resistance transfers some energy to the thermal store of the air — the system becomes open. This is why objects do not reach the theoretical speed predicted by pure GPE → KE conversion.
Practice questions for Energy Stores & Systems
Which energy store is associated with an object that is moving?
Explain what is meant by a 'closed system' in terms of energy.