POWER同energy 有咩分別

power 係功率

即係每秒有幾多 energy lor~~~~

舉例，如果一個heater係300w 既話，開左十秒，就會放左3000J 出黎

Energy (能量) means the work done by some process or action. Unit: [J]

Power means the rate of work done or the rate of energy transfer. In Chinese, we call Power as 功率. Whenever we talk about 率, it always refer to per unit time. Just like 速率 (speed), it means how much distance an object goes per unit time. Unit: [J/s] or [W]

Hence, Power means how much energy is transferred per unit time.

Here are two examples:

Example One:
On the surface of a light bulb, there is always a rated power value, e.g. 100W@220V. It means if I connect the light bulb to 220V power socket, the bulb is expected to give 100W power output.

it means in every second, the bulb is giving out 100J energy. Well, of course, only 10J is approximately converted into light energy, the remaining 90J is dissipated as heat.

Example two:
I use a motor to pull up a heavy box on the ground and I assume there is no further power loss (lossless motor, lossless pulley, no air resistace, etc.). I assume the heavy box is pulled up onto a table, it gains 300J potential energy. The whole process takes about 2seconds.

Then the mechanical power of the box = 300J / 2s = 150J/s or 150W
Since everything is lossless, the mechanical output power of the motor is also 150W.

From example two, we can see one more thing. The calculated power (i.e.150W) is essentially the average power. Because we dont know the details of the process, the motor may use 1.5s to warm up and 0.5s to pull the box up. But since we do not know the details of the process, we can only say about the average power.

If the motor really only uses 0.5s to pull the box up, then the mechanical power output should be 300J / 0.5s = 600W

This is why we have a term called instantaneous power. In fact, if you have learnt about differentiation, instantaneous power is actually the time derivative of energy. So, average power and instantaneous power are different.

Come back to your question. Now you know more about the power and energy. So you can say:

1) in terms of units
Energy: Joule
Power: Joule per second or Watt

2) in terms of meaning
Energy: how much work is done
power: how much work is done per unit time (i.e. in every second)

3) in terms of concepts of *average, instantaneous*
energy: a lumped sum
power: can be divided into average power or instantaneous power

4) in terms of time derivative
power is the time derivative of energy
on the other hand, energy is the integration of power over a period of time

If you ask me to give a presentation on this, I will say things above. I hope I can help. =) Thanks

power= how much energy is transferred per unit time(second)
energy=power X time

2007-02-15 23:18:36 補充：
power= energy/timeenergy= total engery used

Power X time = Energy