Question

What does a matchstick burn on rubbing it on the side of the matchbox?

Answer 1

For this you need to know what initiate burning
burning take place when something reaches it's ignition temperature
by rubbing the matchstick you are providing it friction which converts into heat and raise the temperature and hence help the match stick to attain it's ignition temperature

Answer 2

Matchsticks mainly contains red phosphurous on the top.
And as phosphurous has very low ignition temp. about 35 degree C.
 It is used to glow matchstick by rubbing the phosphrous through rough surface. This leads tofriction and matchstick glows..

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