Fused Matchstick Rocket

Step 6 How it works

(If I'm wrong about any of this, please, comment and correct me!)

A matchstick rocket is, in essence, a small rocket engine on a wooden stick. The head acts as the fuel, and the foil acts as both the combustion chamber and the nozzle.

The tip of a standard safety matchstick contains a chemical called potassium chlorate, which is a powerful oxidizer. When heated (in our rocket, this is done by the fuse), it decomposes into potassium chloride and oxygen:

2KClO₃(s) + heat → 3O₂(g) + 2KCl(s)

potassium chlorate (solid) + heat → oxygen (gas)+ potassium chloride (solid)

In doing this, it releases energy, which causes sulfur (another ingredient in the tip of the match) to burn:

S(s) + O₂(g) → SO₂(g)

sulphur (solid) + oxygen (gas) → sulphur dioxide (gas)

This, in turn, releases sulphur dioxide (which is the culprit behind the smell of burning matches) and more energy, setting the wood of the matchstick on fire.

We're mainly interested in the decomposition of the potassium chlorate, which rapidly produces hot oxygen gas. Gases take up a lot more volume than solids, and the oxygen is therefore at a high pressure while trapped inside the aluminium foil. The heat causes it to expand even more, thus increasing the pressure. The only escape for the oxygen is out through the small gap between the foil and the match - through which it shoots out at high speed. The resulting effect is described by Newton's third law, and is the basis of any rocket engine. As he puts it:

"LAW III: To every action there is always opposed an equal reaction: or the mutual actions of two bodies upon each other are always equal, and directed to contrary parts. — Whatever draws or presses another is as much drawn or pressed by that other. If you press a stone with your finger, the finger is also pressed by the stone. If a horse draws a stone tied to a rope, the horse (if I may so say) will be equally drawn back towards the stone: for the distended rope, by the same endeavour to relax or unbend itself, will draw the horse as much towards the stone, as it does the stone towards the horse, and will obstruct the progress of the one as much as it advances that of the other. If a body impinges upon another, and by its force changes the motion of the other, that body also (because of the equality of the mutual pressure) will undergo an equal change, in its own motion, toward the contrary part. The changes made by these actions are equal, not in the velocities but in the motions of the bodies; that is to say, if the bodies are not hindered by any other impediments. For, as the motions are equally changed, the changes of the velocities made toward contrary parts are reciprocally proportional to the bodies." (see http://en.wikipedia.org/wiki/Newton%27s_laws_of_motion#Newton.27s_third_law:_law_of_reciprocal_actions)

So, when the hot gas is forced out through the nozzle, it is pushing downwards, towards the ground. So, that means an equal force is pushing the rocket upwards - towards the sky. Unfortunately, the potassium chlorate does not burn (and provide thrust) for long, and so the effect is sadly temporary. The thrust is only enough to allow the matchstick to undergo a brief, sub-orbital journey at best - for example, across a backyard.

But, to any aspiring rocket scientists, take heart! Project Mercury started out sub-orbital as well! Keep modifying and improving the design, and you may well be the first to get a matchstick - powered rocket into low-earth orbit ;) .