Physics
A balloon filled with hydrogen will

Reach a particular height and remain floating
Continue going upwards uninterrupted
Burst after reaching some height
Reach a particular height and start coming down

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Physics
Conservation of energy refers to the fact that

Energy cannot be created or destroyed but can be converted from one form to another
If you conserve energy you will not be as tired
No chemical reaction is 100 percent efficient
The entropy of the universe is always increasing

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