English
Energy is money in a sealed wallet: you can change coins for notes, but the total never goes up or down on its own.
Part of ICSE Class 9 Physics on Lipi
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English
The total energy of a closed system stays exactly the same before and after any process.
Falling object
English
PE lost equals KE gained, so the total stays the same. At the bottom all the PE has become KE.
Wasted energy
English
This energy is not destroyed: it just becomes too spread out to do useful work.
Efficiency
English
No real machine is 100% efficient because some energy always escapes as heat or sound.
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Point 1
Point 2
Point 3
Point 4
Point 5
Point 6
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Point 1
Total energy in a closed system is always conserved.
Point 2
Energy transfers (such as PE to KE) keep the total fixed.
Point 3
Dissipation and efficiency explain why some energy is wasted as heat.
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सामान्य भूल
✕ Energy gets used up and disappears.
✓ It is only transferred or changed in form; the total stays the same.
सामान्य भूल
✕ Wasted energy is destroyed.
✓ It spreads out as heat to the surroundings: still there, just no longer useful.
सामान्य भूल
✕ A good machine can be 100% efficient.
✓ Some energy is always lost to friction, heat or sound, so efficiency is always below 100%.
सामान्य भूल
✕ A falling object gains energy from nowhere.
✓ Its kinetic energy comes from the gravitational PE it loses as it falls.