Question

why is it more difficult to burn combustible substances than others

Answer 1

Some substances have a lower combustion point and some substances have higher combustion point. Which substance have lower combustion point they catch fire much more easily and faster as compared to others substances, which have higher combustion point. The temperature at which a substance catches fire is the most important parameter in determining the combustibility of different substances.

Answer 2

Explanation:

It is difficult to pull the boat on the beach because of the friction between the boat and sand. But in the sea, there is less friction between the sea water and the boat. Hence, it is easier to pull the boat in the sea.