Conservation of Energy
Energy cannot be created or destroyed, only transformed.
About this topic
Energy cannot be created or destroyed, only transformed from one form to another or transferred between objects. In a frictionless system, kinetic plus potential energy remains constant, so a roller coaster's speed at any height follows from KE + PE = total.
When friction acts, mechanical energy is converted into thermal energy, but the total energy is still conserved. This makes energy accounting a powerful method: set initial total equal to final total, including any losses. It is often easier than using forces and time, especially on curved paths.
Example: a pendulum released from 0.2 m above its lowest point reaches 2 m/s there, since ½v² = gh gives v = about 1.98 m/s. A 2 kg ball dropped from 10 m has 196 J of GPE at the top and almost all of it as KE at the bottom. Power stations, engines, batteries, food chains and the Sun all involve energy transformations.
Common misconceptions: energy is not used up, but becomes less useful as it spreads out as heat. Also, a perpetual motion machine is impossible because there are always losses. Make sure you include all forms, such as thermal, sound and elastic energy, when summing.
Key ideas
- Total energy in a closed system is constant
- Pendulum swaps PE and KE
- Friction turns it into heat
Quick check
Use cases: where Conservation of Energy helps
- Homework: review the key idea behind Conservation of Energy before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Conservation of Energy without notes.
- Visual learning: play with the interactive lab to see how Conservation of Energy changes when you adjust its inputs.
- Teaching a friend: explain Conservation of 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 Conservation of Energy?
Energy cannot be created or destroyed, only transformed.
What will I learn in Conservation of Energy?
Total energy in a closed system is constant. Pendulum swaps PE and KE. Friction turns it into heat.
Is Conservation of 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 Conservation of 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 Conservation of 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.