Power
Power is the rate of doing work: P = W/t.
About this topic
Power is the rate of doing work or transferring energy: P = W/t, in watts (1 W = 1 J/s). A 100 W bulb uses 100 joules each second. For moving objects, P = Fv.
Two people can do the same work but the quicker one is more powerful. A kilowatt-hour is an energy unit equal to 3.6 MJ, used for electricity bills. Engines and appliances are rated in watts or kilowatts, and one horsepower is about 746 W. Power is not stored; it describes how fast energy flows.
Example: a student with a mass of 60 kg climbs 3 m of stairs in 5 s, doing about 1764 J of work, so the power is about 353 W. A car engine of 80 kW traveling at a steady 25 m/s delivers a driving force of 3200 N. A 2 kW kettle running for 3 minutes uses 0.1 kWh.
Common confusion: power and energy are different. A powerful machine is not necessarily one that does more total work, only one that does it faster. Also take care with units, converting minutes to seconds and kilowatts to watts before calculating.
Key ideas
- Unit: watt = joule per second
- P = Fv
- A kilowatt-hour is energy, not power
Quick check
Use cases: where Power helps
- Homework: review the key idea behind Power before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Power without notes.
- Visual learning: play with the interactive lab to see how Power changes when you adjust its inputs.
- Teaching a friend: explain Power in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Power?
Power is the rate of doing work: P = W/t.
What will I learn in Power?
Unit: watt = joule per second. P = Fv. A kilowatt-hour is energy, not power.
Is Power part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Power lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Power?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.