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How to determine projectile velocity with a phone book

A place to ask general spud cannon related questions.
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Unread postAuthor: qwerty » Thu Mar 22, 2012 5:00 pm

Hmmm, i watched another one of his videos... His eyes... They point in the wrong directions. I'm scared.

L000L, i just watched another of his videos "how to untie a cable tie"
-"so, all you need is a small knife"

No Sh!t.
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Unread postAuthor: Gun Freak » Thu Mar 22, 2012 6:20 pm

Dang man that guy's a genius! PERPETUAL MOTION!!! :D

LOL 16:03 :D :D :D
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Unread postAuthor: D_Hall » Thu Mar 22, 2012 7:58 pm

jackssmirkingrevenge wrote:It's kinetic energy that causes the penetration, not the velocity alone.

To be fair, penetration is a complex topic. It isn't just as simple as kinetic energy. Momentum (velocity), projectile composition, projectile geometry, and projectile orientation are all VERY significant variables.

Heck, there are even situations where identical projectiles shot at identical targets will NOT penetrate further with additional energy; the opposite can be true!

MANY, MANY phenomena are at play when penetration is the subject at hand.
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Unread postAuthor: jackssmirkingrevenge » Thu Mar 22, 2012 11:10 pm

D_Hall wrote:MANY, MANY phenomena are at play when penetration is the subject at hand.


Naturally, and I remember going into some detail here along similar lines: http://www.spudfiles.com/forums/penatra ... t7563.html

In this case however, dealing with a guy who thinks that tap water over a pot lid implies perpetual motion, I has trying to simplify the issue ;)

Guys, please don't direct him to spudfiles...
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Unread postAuthor: jimmy101 » Fri Mar 23, 2012 12:27 pm

Heck, not just ammo and other gun related properties but the characteristics of the phone book itself will also have huge affects on the results. Simple things like how many times the book has been opened, whether it is horizontal or vertical all effect how "hard" the book is.
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Unread postAuthor: Technician1002 » Fri Mar 23, 2012 4:00 pm

I was thinking about the title of this thread. You can use a phone book to find the velocity of a projectile. Can be used for conversion of momentum math. If the projectile hits the phone book at it's CG and does not go through and is retained in the pages, you can use a phone book to do this.

1. Suspend the phone book by a rope under a tree.
2. Use a camera to find how far the book swings when shot
3. Using the combined mass of the phone book and projectile, calculate the energy required to raise the phone book the distance it rises at the end of the swing.
4. Calculate the energy the projectile had prior to impact.
5. Calculate the velocity the projectile using the projectile mass to have that energy.

Double check your math!
:D
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Unread postAuthor: jimmy101 » Sun Mar 25, 2012 2:49 pm

Technician1002 wrote:I was thinking about the title of this thread. You can use a phone book to find the velocity of a projectile. Can be used for conversion of momentum math. If the projectile hits the phone book at it's CG and does not go through and is retained in the pages, you can use a phone book to do this.

1. Suspend the phone book by a rope under a tree.
2. Use a camera to find how far the book swings when shot
3. Using the combined mass of the phone book and projectile, calculate the energy required to raise the phone book the distance it rises at the end of the swing.
4. Calculate the energy the projectile had prior to impact.
5. Calculate the velocity the projectile using the projectile mass to have that energy.

Double check your math!
:D
Then take your results with a huge grain of salt.

A ballistic pendulum is a tricky thing to get accurate numbers out of. One problem is that the ammo and phone book will heat up due to the impact. That's energy from the KE of the projectile but it doesn't end up lifting the phone book. You would probably get more accurate numbers by using a video camera to record the shot then ignore the images and just use the audio track as chrono data. :)
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Unread postAuthor: DYI » Sun Mar 25, 2012 3:10 pm

Jimmy, considering that calculations for the impact speed based on the height of the pendulum are derived from the assumption of an inelastic collision of the projectile into the pendulum (which should hold for a well designed system which doesn't have chunks flying out during an impact), the lost KE (which is usually MOST of the KE) is already accounted for. The typical sources of error in a ballistic pendulum test are rotational motion in the pendulum and mechanical losses in the pivot mechanism. Even without accounting for these, the measurements taken from a well-built ballistic pendulum will be far and away more accurate than anything done with audio recording.
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Unread postAuthor: warhead052 » Sun Mar 25, 2012 5:16 pm

I won't troll his video, but I think we found out who zoroborofaq is now, or even pimpassassing is. His perpetual motion theory is hilarious.
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Unread postAuthor: Brian the brain » Mon Mar 26, 2012 12:57 pm

He's trolling me! :cry:



i will challenge you on youtube! i will hit an empty can with my homemade air gun, and it will not even move, and you hit a fulled can with your gun and try not to make fall not just move,

mouayad888


My answer ( before I realised it's the modified nailgun-gone-atom-bomb-in-a-pipe guy)...
Let's see..

You want to compare two homemade guns using different pressures, different valves, different calibers, different barrel lengths, different chamber volumes, different ammo, both in weight and shape on two different targets (full or empty) and you expect me to act surprised when the results differ?

is that about right?

And then what?

Declare your gun superior to mine when it comes to not moving cans?

What will that proove?

I'm probably just confused..
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Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: Gun Freak » Mon Mar 26, 2012 1:02 pm

Lol and he was trying to tell me I'm jealous :D
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Unread postAuthor: Brian the brain » Mon Mar 26, 2012 1:03 pm

well...you are.

Of his pink cloud.. :D

I took up his challenge.
Guess what..The can moved.
My god..
He's right!

[youtube]http://www.youtube.com/watch?v=wc_i2N8FwXs[/youtube]
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Last edited by Brian the brain on Mon Mar 26, 2012 1:10 pm, edited 1 time in total.
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Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: Gun Freak » Mon Mar 26, 2012 1:06 pm

Image
:D
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Unread postAuthor: warhead052 » Mon Mar 26, 2012 1:31 pm

Who was it that had the 3,000psi air rifle on here? I remember seeing it, it was a coax. Who ever it was needs to post it as a video response and see what happens.
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Unread postAuthor: Brian the brain » Mon Mar 26, 2012 1:41 pm

Gipetto...

Maybe he will understand when we compare his airgun firing at a safe door, to Larda's hybrid.


Say Larda penetrates an inch.
This guy gets 0 penetration.

Larda's projectile travelled at say..mach 2.

mach 2 times 0...
So this guy's ammo did NOT move at all.
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Can't ask for a better compliment!!
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