Question

Why don’t the trees spontaneously catch fire and burn all the time? Why don’t the fires stop immediately as soon as they start?

Answer 1

Answer:

Both of these phenomena is due to the ignition temperature.

Explanation:

Trees don't spontaneously catch fire because there is a temperature above which materials combust. This is called the "ignition temperature." This temperature must be reached before the trees will ignite, and the external condition does not always harbor such high temperature.

Fires don't stop immediately because, while some parts of the flame has cooled down sufficiently below the ignition temperature, other parts of the flame have not. It takes time for all the part of the flame to cool down below ignition temperature for the burning to stop.