Atmosphere and volume - vacuum cannon limitations

In summary, the conversation discusses the use of atmospheric air versus pressurized air in cannon demonstrations. The speaker explains that the use of atmospheric air is more common due to simplicity and cost, but using pressurized air can provide more power. The speaker also notes that the maximum velocity depends on pressure and density, and using high-pressure air may not make a significant difference unless the temperature is also raised. Additionally, the use of pressurized air may be more effective for shorter barrels or heavier projectiles.
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https://physics.csuchico.edu/~eayars/publications/AJP00961.pdf
http://www.phys.utk.edu/demoroom/MECH/The%20Vacuum%20Canon.pdfSo I get the outside atmosphere is what provides air density and such in the pdf above^.
However, why is it that most cannon demonstrations use just the air from the atmosphere? Is this to simplify demonstrations / save on costs?

Basically:

Would it be better to use a pressurized gas chamber around the broken seal area than rely on Earth's atmosphere? Or is my thinking incorrect? If it is better to use a pressurized chamber, then would there be an appreciable change to the formulas presented in the pdf provided?
 
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Limebat said:
Would it be better to use a pressurized gas chamber
Definitely. That's why we tend to use chemical explosions for propelling bullets, rather than vacuum pumps. The Air Bazooka is really just a novelty. If you were to try to propel an artillery shell, you'd need a vast amount of air in a very long pipe as the performance depends on the amount of Energy stored in the 'vacuum'.
An air gun (spring operated) is legally required to have no more than 16J (12 ft lbs). That can be obtained by a modest size spring in a small compression chamber. The Cautionary Note in the first reference points out that the KE of the pingpong ball on exit is a lot higher than that - luckily it soon slows down as it has very poor aerodynamics!

A good fun project, though.
 
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  • #3
Limebat said:
Would it be better to use a pressurized gas chamber around the broken seal area than rely on Earth's atmosphere? Or is my thinking incorrect? If it is better to use a pressurized chamber, then would there be an appreciable change to the formulas presented in the pdf provided?
The maximum velocity depends on Pressure/density. A six feet vacuum canon seems to get close to that velocity already, if loaded with a single ping-pong ball. High pressure air won't help unless you can raise the pressure without raising the density by raising the temperature. Spring piston air guns do this by compressing the air, as do firearms of course. if you just have a high-pressure air reservoir, it likely will not help.
If you had a heavier projectile or a shorter barrel, using pressured air might make more sense.
 
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1. What is the relationship between atmosphere and volume in a vacuum cannon?

The atmosphere and volume in a vacuum cannon are inversely related. This means that as the volume of the cannon decreases, the atmospheric pressure inside the cannon increases, and vice versa.

2. How does atmospheric pressure affect the performance of a vacuum cannon?

The higher the atmospheric pressure inside the cannon, the more force and velocity the projectile will have when it is launched. This is because the air molecules have less space to spread out and therefore exert more force on the projectile.

3. What are the limitations of a vacuum cannon?

One major limitation of a vacuum cannon is that it can only reach a maximum atmospheric pressure of around 15 pounds per square inch (psi). This means that the projectile will not have as much velocity as it would in a true vacuum.

4. How can the volume of a vacuum cannon be changed?

The volume of a vacuum cannon can be changed by adjusting the size of the chamber or by adding or removing air from the chamber. This will affect the atmospheric pressure and therefore the performance of the cannon.

5. Can a vacuum cannon be used in outer space?

No, a vacuum cannon relies on atmospheric pressure to launch the projectile. In outer space, there is no atmosphere, so the cannon would not work. However, a similar concept could be used in space using other types of pressure or force, such as gas or magnetic fields.

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