← ⚛️ Physics · usually met in Std 6-12
The capacity to do work. It cannot be made or destroyed, only moved and changed from one kind into another — which is why there is no such thing as a free machine.
Energy has many forms: motion (kinetic), position (potential), heat, light, sound, chemical, electrical and nuclear. A stretched bow holds potential energy; let go and it becomes the kinetic energy of the arrow. Burning wood turns chemical energy into heat and light. A battery is chemical energy waiting for a circuit.
The law of conservation of energy says the total never changes. When a ball bounces lower each time, the missing energy has not vanished — it has gone into sound, into warming the ball and the floor very slightly. This is also why a perpetual motion machine cannot exist, no matter how clever the drawing: every real machine leaks energy as heat, and no arrangement of parts gets it back.
Want to see it moving? Search YouTube for “Energy” ↗ — we send you to the search rather than to one video, because a link to one video eventually rots.
This entry was written for Star Student in our own words — it is a summary, not a source. Here is where the people who actually hold these facts keep them. Go and check.
Your own textbook ↗Balbharati publishes the textbooks free to read online. Your chapter is the thing to check first — an encyclopedia is a summary, and the syllabus is the syllabus.Last gone through: 1 October 2026 · How these entries are written
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