Physics
The oil in the wick of an oil lamp rises up due to:

Capillary action
Pressure difference
Gravitational force
Low viscosity of oil

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Physics
It is more difficult to walk on a sandy road than on a concrete road because

sand is soft and concreter is hard.
the friction between sand and feet is less than that between concrete and feet.
the sand is grainy but concrete is smooth.
the friction between sand and feet is more than that between concrete and feet.

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