Question

why is it that a needle may float on clear water but will sink when water is heated

Answer 1

Because of heat the density of warm water becomes low.

Answer 2

It's because of heat when it's heated the density of water became low and it sinks.If the surface is agitated to break up the surface tension, then needle willquickly sink. ... Washing with coldwater: The major reason for using hotwater for washing is that its surface tension is lower and it is a better wetting agent. But if the detergent lowers the surface tension, the heating may be unneccessary. This is the reason for it ...

Hope it help...!!