Twitches Science Project V.2. "SNCA"

[TwitchTheAussie]

Well ever since V.1 "Whompah Stompah" blew up from an attack of MAPP gas, I decided to rebuild it. V.2 is finished. I gave it the name "Spray and Click Affair" because thats basically what it is Anyway its just a basic cannon, piezo lighter and a fan. I screwed everything together so it wont separate after every shot, and epoxied it all up.

Had to give a demo today so that went good. Got 150+m with a cut up rubber ball and it gave me good marks just because it outshot the ballista a kid entered.

My problem is this. Being an avid shooter I know what a sonic boom sounds like and my cannon made one. Normally at most combustions make 30-40 psi and my c:b ration is a bit off bout 3:1 and despite the ball being wedged in tight barely halfway down the barrel but it still made a sonic boom.

How is this possible?

[hi]

my guess is that the gas expanding is the sonic boom and not the rubber ball it self.

[TwitchTheAussie]

Thats what I thought thanks man

[f.c]

you got to make a potato cannon for a science project. nice.

[Fnord]

They let you build a gun for a science project in australia? Are they illegal where you live?

[spud yeti]

youre really lucky to have the excuse to build a cannon as a school project! As hi said, its probably just the gas, not the projectile(unfortunately!). Good luck for it, and I hope you get good marks 8)

[frankrede]

How sure are you that you broke the sound barrier?
Chronograph?
I doubt that a run of the mill cannon with a bad C/B and a poorly fitted ammo would break the sound barrier.

[TwitchTheAussie]

The ammo fitted pretty tightly and Ive grown up around guns so I do know what sound something makes when it breaks the sound barrier Frank. And the cops let me off lightly just because I had an official note from the school saying I could make one.

[jimmy101]

Not a chance that you broke the sound barrier.

You can not tell how fast a round is going by just the sound. A very experienced shooter might be able to tell after firing many rounds of a particular caliber and varying loads and chrono'ing every shot. But, that knowledge would be completely useless when it came to a round as different as a "rubber ball". He would have to go through the entire process with the new round; multiple shots, varrying loads and a chrony, to learn what supersonic sounds like for the new round.

A spud gun does not have to be supersonic to make a hell of a lot of noise. A large CB ratio will make the gun much louder than it would be with a more reasonable CB. The sound you heard was nothing more than the "bang" of the gun itself.

[TwitchTheAussie]

I never said it was the ball. I was just confused about how gases at 30-40 psi could break the sound barrier. Once again I will say in bold I know it wasnt the rubber ball I was just confused about how gases at 30-40 psi could break the sound barrier. I know Im not making much sense but I have personal reasons for it.

I just didnt think 30-40 psi would break the sound barrier by itself.

[Modderxtrordanare]

You didn't break the sound barrier.

[wannabie]

i agree with modder i highly doubt that you broke the sound barrier.... sorry to break your bubble lol

[jackssmirkingrevenge]

30-40 psi is 15-25 psi more than the atmosphere, with that sort of impetus given the right conditions there's no reason why gasses shouldn't accelerate past the speed of sound.

[wannabie]

hmm i guess but then again i dont really get what you just said... so if i slightly understand what you just said and the gasses did reach the speed of sound isnt that what DDT is?

[jackssmirkingrevenge]

DDT? Isn't that a pesticide

Gasses reaching the speed of sound will make a sonic crack, that's why explosions are so friggin loud