The idea of a vacuum bazooka might seem like something out of a science fiction movie, and in fact there’s an amusing side about it, given that you can make it at home. Yet it is a scientifically useful device, based on a simple but effective physical principle: the difference in atmospheric pressure.
First proposed in 2001 by Neil A. Downie, the vacuum bazooka is mainly used in educational and experimental contexts.
Its operation is ingenious but simple: it consists of a tube in which a vacuum pump (sometimes a normal vacuum cleaner) reduces the pressure in front of the bullet. At that point, the external air, pushing on the back, accelerates it along the tube, making it reach surprising speeds.
The structure is rather simple: a straight tube closed at the ends by an aluminum bursting disk (usually 2-4 layers) and by the bullet itself. A connector, near the exit opening, is used to create a vacuum. When the bullet is released, atmospheric pressure pushes it forcefully forward, causing it to break through the rupture disk and then continue at high speed.
A bullet fired from a vacuum bazooka can reach about 1,050 km/h, although this value can vary depending on the configuration and materials used. It is interesting to note that the theoretical maximum speed is independent of the mass of the bullet or the diameter of the barrel.
This very useful device is mainly used to demonstrate the principles of vacuum physics and fluid dynamics (nothing to do with the arms race we hear so much about these days, fortunately!)
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