What is the optimal barrel length for maximum distance in a blow-gun?

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SUMMARY

The optimal barrel length for maximum distance in a blow-gun is determined by balancing the internal propulsive pressure and the projectile's exit velocity. The barrel volume, calculated as area multiplied by length, should allow the pressure to equal atmospheric pressure just as the projectile exits. A barrel that is too short wastes air, while one that is too long causes the projectile to decelerate due to friction and air resistance. Practical experimentation combined with calculus can help refine the calculations for achieving maximum distance.

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  • Understanding of basic physics principles, particularly pressure dynamics.
  • Familiarity with projectile motion and air resistance concepts.
  • Knowledge of calculus for optimizing velocity functions.
  • Experience with practical experimentation and data analysis.
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  • Research the relationship between barrel volume and projectile exit velocity.
  • Study the effects of air pressure on projectile performance in blow-guns.
  • Learn how to apply calculus to optimize projectile motion equations.
  • Conduct real-world tests to gather data on various barrel lengths and their performance.
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Hobbyists, DIY enthusiasts, and physics students interested in optimizing the performance of blow-guns or similar pneumatic devices.

funkyreuben
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I recently made a few mini-marshmallow blow-guns out of PVC and I noticed that different barrel lengths provided different firing ranges. Does anyone know how I can calculate the optimal barrel length for maximum distance? I haven't done anything physics related since college (2002) and I'm drawing a blank as to calculating this. Any help would be greatly appreciated.

Chris
 
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Welcome to PF, Funkyreuben.
I'm not exactly sure how you would go about this. It depends upon the air source volume and pressure. Ideally, the barrel volume (area x length) should be such that the internal propulsive pressure reaches atmospheric just as the projectile is leaving the muzzle. If the barrel is too short, a lot of your air will be wasted; if it's too long, the marshmallow will begin to decelerate due to friction and air resistance before it can get out.
Trial and error might be the easiest approach.
 
Thanks! I plan on doing some real world testing but I was hoping for a way to calculate it as well.

Chris
 
if you were to write velocity as a function of either area or length you could use calculus to maximize the escape velocity... I don't know how hard that would be though
 

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