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finding force using volume and psi HELP!!!

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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finding force using volume and psi HELP!!!

Unread postAuthor: kydavies » Thu Apr 22, 2010 9:17 pm

how can you find the force in Newtons without using kinematics and only using the size of your air tank and what psi its at?
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Unread postAuthor: btrettel » Thu Apr 22, 2010 9:45 pm

Welcome to SpudFiles.

Force on what from what? This post is very vague. Describe what you want in more detail.
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Re: finding force using volume and psi HELP!!!

Unread postAuthor: MrCrowley » Thu Apr 22, 2010 9:48 pm

kydavies wrote:how can you find the force in Newtons without using kinematics and only using the size of your air tank and what psi its at?

Force = Pressure x Area

Force in Pounds
Pressure in Pounds per Square Inch
Area in Inches

So if your barrel is 2" in diameter (pi x 1^2) = 3.14 inches^2 and has 100PSI in it, assuming the projectile is a good fit in the barrel, there will be 314 pounds of force on the projectile.

edit: Then convert that to Newtons.
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Unread postAuthor: c11man » Thu Apr 22, 2010 9:52 pm

i think he is trying to fine the potential energy in the chamber maybe?
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Unread postAuthor: Hubb » Thu Apr 22, 2010 10:13 pm

I bet he's trying to find out the kinetic energy from when the round strikes a target.

What's the poll up to?

To answer the question properly, however, you should do what btrettel suggests. A good start for you, though, is to learn and use GGDT.
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Unread postAuthor: saefroch » Fri Apr 23, 2010 10:08 am

Volume of air tank has no effect on force on the internals, just surface area and pressure. What are you trying to find? A certain force on part of the internals? If the materials you are using for your chamber will hold?
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Unread postAuthor: SpudBlaster15 » Fri Apr 23, 2010 1:34 pm

Maybe he's looking for the average force on the projectile during its travel down the barrel, which will depend on the volume of the chamber, as well as the starting pressure.

Hard to answer such a vague question though.
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Unread postAuthor: kydavies » Fri Apr 23, 2010 8:42 pm

sorry about the vague question but i built a 9' tall potato cannon and i have no safe place to shoot it thats near by so i cant time how long the potato is in the air for so kinematics is out. i needed to find the buzzel velocity of the cannon without firing it. to do that i need the force the pneumatic chamber exerted on the potato so that i could use F=ma to find the acceleraion then multiply it by my barrel length (10'). thanks for the help MrCrowley :D
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Unread postAuthor: kydavies » Fri Apr 23, 2010 8:46 pm

info
70psi 1.5 diameter barrel potato mass=.25kg barrel length= 3.2m does somone want to do this math for me cause my brain just aint working right now and i dont have time. let me know if you need anymore info
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Unread postAuthor: saefroch » Fri Apr 23, 2010 9:44 pm

Assuming that the 70 psi stays constant after you open whatever valve it is (which it doesn't, especially as the spud travels down the barrel, it may be worth it to calculate the jerk because the number I will supply here is greater than actual), the spud experiences an acceleration of 2.51 m/s^2.

Area of spud acted on by pressure- 0.00114 m^2
Area of spud acted on by pressure- 1.77 in^2
Force experienced by spud- 123.7 lbs
Force experienced by spud- 550.24 N
Acceleration of spud- 2,200 m/s^2
Muzzle velocity of spud- 118.7 m/s

That's the best I can do for you, since I don't know how to account for the depressurization behind the spud as it travels down the barrel. I would need to know your chamber volume to calculate that- not that I'm sure I could.

Please remember, THE MUZZLE VELOCITY IS INFLATED. Given the chamber volume, I will do my best to give a better approximation.

EDIT: I cannot supply the maths for a varying force, which is exactly what would be exerted on the spud as it travels down the barrel, since I am unfamiliar with calculus. I sure could probably find a friend to do so for me, if you are willing to wait.
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Unread postAuthor: kydavies » Fri Apr 23, 2010 11:06 pm

info
70psi 1.5 diameter barrel potato mass=.25kg barrel length= 3.2m does somone want to do this math for me cause my brain just aint working right now and i dont have time. let me know if you need anymore info
:?
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Unread postAuthor: saefroch » Fri Apr 23, 2010 11:07 pm

Chamber volume? The math I gave you is as accurate as most will get, and as accurate as possible without calculus.
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Unread postAuthor: kydavies » Fri Apr 23, 2010 11:08 pm

oops i re posted but fork calculus its to much works all i wanted was a rough velocity thanks for the math
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Unread postAuthor: saefroch » Fri Apr 23, 2010 11:10 pm

I agree, fork calc. And now that I figured out how to do the math for your gun... I should do it for mine and see if it matches my audio chrono estimate.
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Unread postAuthor: kydavies » Fri Apr 23, 2010 11:11 pm

the chamber length is about 110 inches (2'' PVC) :lol:
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