Question

Explain why a paper cup easily catches fire but a paper cup filled with water does not catch fire.

Answer 1

A substance catches fire only if the heat provided is more than or equal to its ignition temperature. A substance cannot catch fire if its temperature is below its ignition temperature. A paper cup when heated acquires sufficient heat to reach its ignition temperature and easily catches fire. But if the same paper cup is filled with water then the heat provided to the cup gets transferred to the water. The cup does not reach the ignition temperature and hence does not catch fire.