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⚡ Energy Transfers in a System

Spec 6.1.2.1 📗 Foundation
📖 In-Depth Theory

Conservation of Energy

The LAW OF CONSERVATION OF ENERGY:
Energy cannot be CREATED or DESTROYED — it can only be TRANSFERRED between stores or DISSIPATED.
In a CLOSED SYSTEM:
Total energy before = Total energy after — always.
EXAMPLES:
Swinging pendulum: KE ⇌ GPE, cycling continuously (ignoring air resistance).
Bouncing ball: GPE → KE → elastic PE → KE → GPE → lower each time (energy dissipated).
Battery-powered torch: chemical → electrical → light + thermal.
Energy is never destroyed — but it can become less USEFUL when it spreads out into the thermal stores of the surroundings.

Dissipation of Energy

DISSIPATION: energy transferred to less useful stores — typically the thermal stores of the surroundings.
Dissipated energy is described as WASTED — not used for the intended purpose.
Causes of dissipation:
FRICTION — between moving parts → thermal energy.
AIR RESISTANCE — object transfers energy to air.
ELECTRICAL RESISTANCE — current in wires → heat.
SOUND — vibrations dissipate energy to the air.
Once energy is dissipated into the surroundings, it spreads out and becomes very difficult to use again.
EXAMPLES:
Car: chemical PE → useful KE + wasted thermal (engine, brakes, air resistance).
Filament bulb: electrical → useful light (10%) + wasted thermal (90%).
Phone charging: electrical → chemical store + thermal (phone gets warm).

Reducing Unwanted Energy Transfers

LUBRICATION — oil between moving parts reduces friction → less thermal wasted.
STREAMLINING — aerodynamic shapes reduce air resistance → less energy to air.
INSULATION — reduces thermal transfer to/from surroundings:
Thick walls, double glazing, loft insulation, cavity wall insulation.
BETTER CONDUCTORS — lower resistance in wires → less electrical energy wasted as heat.
SUPERCONDUCTORS — zero resistance at very low temperatures → zero electrical energy wasted.
There is always a practical limit — beyond a certain point, the cost of further improvements outweighs the energy saved.
⚠️ Common Mistake

Energy is NEVER destroyed — it is dissipated to less useful stores. 'Lost' energy has been transferred to the thermal energy of the surroundings — it is still there, just spread out and difficult to use again. Never say energy is 'used up' or 'gone'.

📌 Key Note

Conservation of energy: never created or destroyed. Dissipation: energy spreads to surroundings as thermal — less useful. Reduce by: lubrication (friction), streamlining (air resistance), insulation (thermal loss), better conductors (electrical resistance). Wasted = total input − useful output.

🎯 Matching Activity — Reducing Dissipation

Match each energy dissipation cause to its solution. — drag the symbols on the right to match the component names on the left.

Friction between moving parts
Drop here
Air resistance on moving objects
Drop here
Thermal loss from buildings
Drop here
Electrical resistance in wires
Drop here
Insulation — thick walls, double glazing, loft insulation reduce conduction rate
Streamlining — aerodynamic shape lets air flow smoothly, less energy transferred to air
Lubrication with oil — reduces surface contact, less thermal energy wasted
Thicker wires or lower-resistance materials — less heat generated by current
🎯 Test Yourself
Question 1 of 2
1. A pendulum swings and eventually stops. Where has the energy gone?
2. Why does adding loft insulation reduce heating bills?
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