Physics
Pieces of camphor placed on water move about rapidly. This is because of

Surface tension
Viscosity
Capillarity
Diffusion

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Physics
Water pipes in hilly areas often burst on a cold frosty night, because

The material of which pipes are made contracts due to cold and so breaks
Water in the pipes freezes and on freezing water expands, so pipes break
None of these
Frost makes the pipes rusty, so they break

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