Library / Foundations: Physics / FPH-11
Foundations: Physics
Power from energy and time
Mean power from energy transferred per second.
- Ref
- FPH-11
- Rev
- v1
- Field
- Foundations: Physics
- Result
- P [W]
Mean power is energy transferred per second. Energy in joules and time in seconds give power in watts.
Power tells how quickly energy is transferred: more energy in less time means more power.
Calculator
W
J
s
- Power in kW0.24 kW
- Energy in kWh0.002 kWh
What drives the result
Each variable is moved across its typical range while the others stay at the values above. The longest bar is the key driver.
Power (W) current value 240 W
EEnergy transferredKey driver
0.33333,300
tTime
27,200
- 1 W = 1 J/s. A kilowatt-hour is the energy of 1 kW for one hour, 3.6 MJ.
- The same job done faster needs more power, not more energy.
Chart data as tables
Ranked variables
| Variable | Typical range | Lowest result | Highest result | Swing (W) | Local step | Change in result |
|---|---|---|---|---|---|---|
| E Energy transferred | 10 to 1,000,000 J | 0.3333 | 33,330 | 33,330 | +10% | +10 % |
| t Time | 1 to 3,600 s | 2 | 7,200 | 7,198 | +10% | −9.09 % |
Sweep of Time
| Time (s) | Power (W) |
|---|---|
| 1 | 7,200 |
| 2.783 | 2,587 |
| 7.746 | 929.5 |
| 21.56 | 334 |
| 60 | 120 |
| 167 | 43.12 |
| 464.8 | 15.49 |
| 1,293 | 5.566 |
| 3,600 | 2 |
Sweep one variable
Power (W)Hover, touch, or use the arrow keys on the chart
Variables and how each one contributes
P
Power
What the equation gives you. Everything else feeds it.
E
Energy transferred
Energy moved or converted. Directly proportional.
t
Time
Time taken. Inversely proportional.
Worked example with the values above
- Energy 7,200 J over 30 s.
- Divide: 7,200 / 30.
- P = 240 W.
Assumptions and limits
- Power averaged over the time.
- Energy and time in SI units.
Common mistakes
- Mixing joules with kilowatt-hours.
- Using minutes for t.
Statistics and uncertainty
Timing error dominates for short events, like a 1 s error on a 30 s test (about 3%).
Where it is used
- Rating motors and heaters.
- Battery drain estimates.
Maths you need
- Energy: joule
- Rates: amount per second