For example, if I took a butane lighter & fired it up, there’s no force in any direction. How does a rocket ignition work & propel itself upwards?
Thanks,
In: Engineering
There IS a force with a butane lighter – it’s just small enough you won’t notice. I’d have to do a lot of math to figure out how much; but its probably measured in fractions of a gram – maybe grams.
You get more force based on how fast you can expel the gasses, how much energy is in the burning, and how much of the burning energy you can capture. Butane lighters mostly just let the gas go, and while the burning is hot (about 4000F), there isn’t a lot of effort to turn that heat into force. In contrast, rocket engines put the gas out a bit faster; burn slightly hotter (about 5000F) – but do a LOT to make sure as much of the burning energy as possible turns into movement.
And you can see the difference: Butane lighters are open flames, meaning most of the force goes in different directions and is lost. In contrast, rocket thrusters are shaped close to a cone – the exact shape is called a “[de Laval nozzle](https://en.wikipedia.org/wiki/De_Laval_nozzle)” – and are made specifically to turn as much energy as possible from burning to thrust.
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