What does gunpowder do?

Answer 1

Gun powder by its self does nothing ... gun power is an incendiary meaning it burns at a high temperature... making it good to project or propel object at a great distance...

Gunpowder is what is known as a "low" explosive. Gunpowder, when ignited by flame or friction (i.e. it is heat in some form that cause gunpowder to ignite), burns rapidly. This rapid burning of the gunpowder grains results in a significant amount of gas being produced. This hot gas expands quickly, producing a wave of force.

In a confined space, this gas will attempt to push against the walls of whatever is confining it. It thus makes for an excellent propellant - gunpowder produces a steadily increasing amount of gas over a relatively long time period (hundreds of milliseconds), allowing it to slowly accelerate a projectile out of a barrel.

In comparison "high" explosives (such as TNT) don't actually burn in the sense of combining with oxygen in a typical oxidation process. Rather, they detonate, and producing a supersonic shock wave of force, and it is this wave which exerts extreme force on objects. Compared to gunpowder, the shock wave from a high explosive is produced about a 10 times faster than the burning gases, and is well over 10 times more forceful. High explosives generally make very poor propellants, since this large force acts over too short a time frame to push a projectile out of a tube - rather, using a high explosive substance as a propellant will most likely burst the barrel or destroy the projectile.