How it works
Power is how fast energy flows: joules per second, measured in watts. Same work done in half the time means double the power.
Humans are surprisingly weak machines. A fit adult sustains ~100–200 W; a Tour de France rider ~400 W for an hour; a kettle draws 2,000–3,000 W.
Use it in real life
Home appliances: the wattage on the label × hours of use = your energy bill. A 2 kW heater running 5 hours costs the same as a 10 W LED bulb running 1,000 hours.
Fitness: a smart trainer showing 250 W means your legs are doing a quarter of a kettle's job.
Car shopping: 100 kW ≈ 134 hp. Power determines acceleration at speed, which is why overtaking ability is a power question, not a torque question.
Frequently asked questions
What's the difference between watts and kilowatt-hours?
Watts measure the rate of energy flow; kilowatt-hours measure the total delivered. A 1,000 W device running for 1 hour uses exactly 1 kWh — that's the unit your electricity company bills.
How much power can a human produce?
Roughly 100–200 W sustained for ordinary fit adults, up to ~400 W for elite endurance athletes over an hour, and 1,500–2,000 W for a second or two in a sprinter's peak effort.
Why do horsepower and watts both exist?
History. James Watt invented 'horsepower' to sell steam engines to people who owned horses. 1 hp = 745.7 W. Watts are the SI unit; horsepower survives in car marketing.