Re: My teacher boiled water in a paper cup,why didn't it burn?

Dear Student:
Paper, which is essentially wood, must reach a flash point in order to burn.  
Different substances have different flash points, and since the cup did not 
burn when the water was in it, this would indicate that the flash point of 
the paper was above the boiling point of water, which as you know is 100.0 
degrees celcius.  When the water is poured out, the paper is now able to be 
heated above that flash point, and it burns.

Thanks for the question, and you keep on asking questions.

Robert L. Judge