Kinetic Energy
The energy of motion: ½mv².
About this topic
Kinetic energy is the energy an object has because of its motion: KE = ½mv². Because it depends on the square of speed, doubling the speed quadruples the energy, which is why high-speed crashes are so destructive.
Kinetic energy is a scalar and is always positive. It is changed when work is done: it rises when a net force speeds up an object and falls when friction or brakes slow it. Its unit is the joule. It depends on speed, not velocity direction, so a ball moving left or right has the same value.
Example: a 1000 kg car at 10 m/s has 50,000 J, but at 20 m/s has 200,000 J, four times as much. A 0.02 kg bullet at 400 m/s has 1600 J, more than a heavy bowling ball rolling gently. Braking systems must absorb this energy as heat, and wind turbines capture the kinetic energy of air.
Tip: a common error is forgetting to square the speed, or squaring only part of the expression. Remember also that kinetic energy depends on the frame of reference, since speed does.
Key ideas
- Doubling speed quadruples KE
- Always positive
- Unit: joule
Quick check
Use cases: where Kinetic Energy helps
- Homework: review the key idea behind Kinetic Energy before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Kinetic Energy without notes.
- Visual learning: play with the interactive lab to see how Kinetic Energy changes when you adjust its inputs.
- Teaching a friend: explain Kinetic Energy 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 Kinetic Energy?
The energy of motion: ½mv².
What will I learn in Kinetic Energy?
Doubling speed quadruples KE. Always positive. Unit: joule.
Is Kinetic Energy 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 Kinetic Energy 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 Kinetic Energy?
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.