Downhill Energy

Why it matters

Follow 100 joules into a filament bulb: 10 come out as light, 90 leak away warming the room. Nothing was destroyed — but those 90 J will never work again. Energy retires.

The idea in plain words

The one-way street. Tap the terms.

total conserved · usefulness degraded

A motor takes 500 J and delivers 400 J of lifting. Efficiency and fate of the rest?

80% efficient; 100 J degraded to warmth and sound

• the law's fine print: degradation — every conversion sheds some energy as disordered heat — the fraction useful never reaches 100%
• the scorecard: efficiency — useful out ÷ total in: filament ~10%, LED ~40%, motor ~80%
• the takeaway: why it matters — can't recycle warmth back into work → conserving energy means conserving USEFUL energy
• η = 400/500 = 80%
• 100 J → friction heat and hum

Predict first

The 'lost' 90 J of heat from the bulb is…

Conservation says the books balance; degradation says the CURRENCY devalues. Diffuse warmth can't be re-collected into useful work.

• still in existence but too spread out to be useful — DEGRADED — correct
• destroyed
• stored in the bulb for later

What you do

Send 100 J through all three devices, compare their useful shares — then answer where the rest went.

Check yourself

A machine with 100% efficiency would…

Friction, resistance and radiation always take their cut. Perfection is an idealisation.

LEDs replaced filament bulbs mainly because they…

Same lumens for a quarter of the joules — efficiency is the whole sales pitch.

Rub your hands and they warm up. The degraded energy came from…

Chemical (food) → mechanical (rubbing) → heat (useless but cosy). A degradation chain you can feel.

• violate degradation — some heat loss is unavoidable in practice — correct
• be common — most machines achieve it
• create energy
• convert far more of the input into LIGHT and less into waste heat — correct
• look modern
• are brighter regardless of energy
• your muscles' work against friction — correct
• the air
• nowhere — warmth is free