Work, GPE & KE
2 guided lessons · 18 checks · 4. Energy Resources and Energy Transfers → Work, Power & Energy Resources
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Lesson 1 of 2
Conservation links work, GPE and KE
Energy never appears from nowhere. When a force works over a distance it moves energy mechanically between stores, and conservation of energy insists the books balance: what leaves one store arrives in another, with the work done as the receipt.
What you know already
Real machines shuttle energy between stores: a thrown ball trades gravitational potential for kinetic and back again. These lessons connect work, GPE and KE through conservation of energy, then practise the perfect-transfer sums that exam questions reward.
Key points of understanding
- GPE names the gravitational potential store and KE names the kinetic store.
- Mechanical work is the transfer route: a force acting over a distance moves energy between stores.
- Conservation of energy keeps the total constant, so the energy transferred equals the work done.
- Pendulum swings shuttle energy back and forth between the kinetic and gravitational stores.
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1.Conservation links work, GPE and KE
Energy never appears from nowhere. When a force works over a distance it moves energy mechanically between stores, and conservation of energy insists the books balance: what leaves one store arrives in another, with the work done as the receipt.
Key points
- GPE names the gravitational potential store and KE names the kinetic store.
- Mechanical work is the transfer route: a force acting over a distance moves energy between stores.
- Conservation of energy keeps the total constant, so the energy transferred equals the work done.
- Pendulum swings shuttle energy back and forth between the kinetic and gravitational stores.
First pass
Two vaults, gravitational and kinetic, with work done as the courier between them. Nothing is minted or destroyed in transit — the courier's manifest (joules of work) matches the deposits and withdrawals exactly.
Analogy — A bank transfer: one account falls, the other rises by the same amount, and the transfer slip (work done) records the identical figure.
Exam pointer — When describing transfers, name both stores and the courier — 'energy is transferred mechanically from the kinetic store to the gravitational store'.
Going deeper
Conservation of energy binds the three quantities: the work done by a force over a distance equals the energy transferred, and that energy arrives in or departs from named stores. In ideal swings the kinetic and gravitational stores exchange the whole amount, each emptying as the other fills.
Analogy — A perfectly sealed pipe loop: whatever volume leaves the tank on the left arrives at the tank on the right, with the pump meter (work done) reading the flow.
Exam pointer — Use the store names precisely — 'gravitational store' and 'kinetic store' — and attach the transfer route (mechanical work) to collect full description marks.
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2.Perfect transfers and energy equivalency
Exam calculations often declare a perfect transfer: no energy wasted, so the stores can be equated directly. Assuming air resistance and friction away lets the GPE lost by a fall equal the KE gained, unlocking speed and height predictions.
Key points
- A perfect energy transfer wastes nothing, so the energy leaving one store equals the energy entering the next.
- Questions signal the assumption by telling you to ignore air resistance or friction.
- With a perfect transfer, the decrease in GPE equals the increase in KE, so the two can be equated.
- Real transfers always leak some energy, which is why the perfect assumption is a modelling choice.
First pass
When a question grants a perfect transfer, the two stores mirror each other exactly: whatever drains from one fills the other. That single permission turns two hard quantities into one equation.
Analogy — Two water tanks joined by a flawless pipe: drop the level in one, and the other rises by exactly the same volume — no drips, no leaks, no losses.
Exam pointer — Spot the trigger words 'ignore air resistance' or 'frictionless' — they license equating the stores in your calculation.
Going deeper
Energy equivalency under a perfect transfer sets the magnitude of the gravitational store's decrease equal to the kinetic store's increase. The assumption is warranted only when the question declares wasted transfers negligible; real transfers always route some energy to thermal stores.
Analogy — An idealised accounting rule: 'no leakage' lets you subtract one column and add the same figure to the other without an audit trail of losses.
Exam pointer — State the assumption in words before equating the stores — 'friction is ignored, so the transfer is perfect' — then carry the arithmetic through.
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Guided content from the SME authoring corpus — note rn_p3SDZQRDzPCYhztZ, pinned at c40b8b284935 · promoted SyllabAI/syllabai-resources b3caaaa90c5e