Power
How fast energy is transferred. Power = energy / time, measured in watts (W). One watt is one joule per second.
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Analogy
Two people climb the same stairs. The quicker one has more power, because the energy moved is the same.
Example
energy = 360,000 Jtime = 180 spower = 360,000 / 180power = 2,000 W
In practice
A 2,000 W kettle moves 2,000 J of electrical energy into the water every second.
Practice
Flashcards
- What is power and what is its unit?Power is energy transferred per second. Its unit is the watt (W).
Interview questions
- A 60 kg student climbs stairs 3 m high in 6 s. Take g = 10 N/kg. Calculate the work done and the power.
- Gain in GPE = 60 x 10 x 3 = 1,800 J
- Work done equals the energy transferred, 1,800 J
- Power = 1,800 / 6 = 300 W
Questions people ask
What is the difference between energy and power?
Energy is how much is transferred, in joules. Power is how fast it is transferred, in watts. A 60 W bulb and a 100 W bulb can both run all day, but the 100 W bulb transfers energy faster and so uses more energy in the same time.
How do I calculate power from work done?
Divide work done by the time it took: P = W / t. If you do 600 J of work lifting a box in 3 seconds, your power is 200 W. Make sure the time is in seconds and the work is in joules before you divide.