Ball deformation

[CHK6]

I was wondering if AGD during testing was able to see any ball deformation from the bolt impacting the paintball? Was it uniform along the equator of the paintball seam? Did non-uniform bulging occur?

Tom states that the paintball under goes 1500 G forces in acceleration and it's hard for me to imagine that the gelatin shell and liquid filling doesn't deform. I know that under 1500 Gs golf balls deform when struck with a club, so I figured the same was or general priciples should apply to paintballs.

My only thinking is under how much pressure will gelatin shell buldge or the paint inside the ball compress?

[Cha0tic]

i believe that the shell itself does not actually become deformed as it accelerates. the paint inside it does distort the movement of the paint though.

coat your barrel with baby powder. stick a ball in the and shoot it. you will see the way the ball travels by seeing how the equator moves around. you will see 2 lines (the equator of the paintball) in the barrel.

[CHK6]

I'm currious if the ball deforms at the point of contact from the bolt and/or blast of gas when at rest? Not the deformation caused by acceleration.

With all balls in sports (except a few that use wooden balls) the balls deform on point of contact; even golf balls and baseballs.

I'm thinking the answer is no because the mass of the paintball is so small and resistence to change is pretty small.

I'm asking these questions because I'm currently writting a paintball physics API in C and from my reading in Fluid Mechanics how an object travels in a pipe depends on the shape of the object. If deformation doesn't occur then this makes the formulas easier to write into an API.

AGD has shown the most open involvement in their studies to the public and was hoping to clear this up for me. It's one thing to figure this out on paper by myself, but physics has shown that experimentation is the true solver.

P.S. You wouldn't happen to have any ideas or answer to my Torsional Modulus question would you?

[Cha0tic]

sorry for not clarifying...i don't like typing that much :)

i'm not sure on the torsional modulus questions.

your best bet would be to do a search on ball deformation. i think Tom Kaye has posted somthing about it in the past.

[ShinyGuy]

Being a gas pressure rather than solid body the force of the blast of air is exerted as a normal force on every point of the ball. Since the ball is accelerating through the air in front of it the pressure in front of the ball is equal to the pressure behind the ball. (actually the pressure in front of the ball is equal to the pressure behind the ball minus the friction between the ball and the barrel. AGD's test could probably tell us if this difference is negligible or not.) Since the ball has an equal force on it from every direction it has no reason to deform. It might become a little smaller as it goes down the barrel but that won't really effect anything. A good comparison would be asking if SCUBA divers deform when they're down at 80-90 feet.


As for the impact of the bolt; My guess is that the bolt doesn't really hit the ball all that hard compared to the burst of gas. If AGD want's to send me geometry file for a mag body I'll mill one out of lexan. It probable wont last long but we should be able to get a few shots off with a high speed camera looking at it. (I don't have the camera but if someone else does we should try it.)

[CHK6]

Thank you very much for your replies. But the more you know the more questions you have. So if you care bear with me I have a few questions.

You state the pressure behind and in front of the ball is the same. Since pressure is nothing more than force over a given area and two eual and opposing forces cancel each other out. With no greater force acting on the ball then how does the ball move?

Do divers deform at 80-90 feet? I believe so but very little and not to noticiable by the diver. If you take a styrofoam cup and tie to it a stone and drop it in the ocen down a couple thousand feet and then bring it up the cup should have deformed smaller to the size of a shot glass. This is due to the pressure excerted on the cup. Same priciple in centifugal tests where test subjects pass out. When you watch the test it looks like there is wind in their face when it's just the pressure of force acting on them. Remember Tom said the ball undergoes over 1K G-forces. I'd be surprised that gelatin doesn't change shape under that kind pressure. But then again the ball doesn't have much resistence to change. I really don't know the answer.


As for a lexan body to see the impact would be extremely interesting. Even if nothing comes out of the experiment, we gain the insight to know that nothing happens.

[Gunga]

Originally posted by CHK6
Do divers deform at 80-90 feet? I believe so but very little and not to noticiable by the diver.

Well, I don't know about me "deforming" when I'm diving at 80+ feet. I'd say that being compressed would be a more accurate term, as the pressure surrounding the diver is equal on all sides.

Take a wetsuit for example of compression. As you dive deeper and deeper, the neoprene wetsuit compresses. More specifically, a 7mm thick wetsuit compresses to something like 3mm at those depths. I think there's some more 'exact' data somewhere, but I don't have it around here.

[Shaft]

Somewhere on this site I read that AGD has done experiments to see the deformation.

[MagNumPI]

I don't think there is any deformation from the bolt. air mabey a little. When you hit a baseball it deformes cause your causing enough of an impact to change it's direction, Golf balls change form due to the velocity of the club. Paintballs aren't struck by the bolt they are "agressivly pushed" (Like that term!!) then blasted by a pop of high air pressure. Deformation occures probably in the in the first 1/2 to 1" of the barrel then the ball reverts to its some what normal shap.

My theory (did a paper on Paintball for physics.. got an 87%, BOOYAA!)

[ShinyGuy]

When you take a Styrofoam cup down 2000 feet it comes back smaller but exactly the same shape. It has an equal force on it from all directions so the material compresses but it doesn't have any un-opposed force to deform it. The same is true of your wetsuit <mutters something about walking three blocks up the hill from the beach with tank, weights and a wet 14mil wetsuit>.

As for why the ball has an equal pressure in front of it; the ball has to push the air out of the way in front of it. The ball would accelerate at a much higher rate than it does except that its motion forward builds pressure in front of it. (it would accelerate at the limit that air can expand based on the amount of molecular motion in it if there were vacuum in front of the ball) the point at which the pressure in front of the ball is equal to the pressure behind the ball defines the point at which the ball accelerates. Look in your physics book if you want the exact equations. (like I should do. It's been so long since I've studied any of this.)

As for the centrifuge example, remember that deformation is being caused by internal forces (the acceleration acting on the mass of the person). Paintballs may deform due to the internal forces (the fill probably does somewhat). How much if dependant of the mass and frigidity of the materials they're made of.

[Vegeta]

I never could belive the whole 1500 g's thing. I couldn't see how a little ball that fragile oculd withstand that much force, especially if it was rubbing against the barrel, without breaking. If the entire human body was suddenly given that much force upon it, all the air pockets, cells, everythign would im/explode.. not pretty. I used to not belive it. or not want to belive it. I htough.. well.. humans have gone well over 300 feet per second right (300fps = 204.96mph)? But hten i realized they hadn't done it in 1/10th of a second. Ouch.

[hardr0ck68]

dear lord what physics classes have you guys been takin? lord did i go to a crudy college, im takin phy 203 and its like highschool all over again THIS IS THE STUFF I WANNA BE LEARNIN :mad:

[Vegeta]

After seeing your reply, I went to see what I had said on this..

Then just had to re-invision that human body x 204.96mph x 1/10 of a second x gravity... hehehe.. thats just cool..

[AGD]

Ok I am jumping in here. Good discussion guys, mostly on track, with good points brought up by all. A credit to what Deep Blue stands for.

The ball does go through thousands of G's of acceleration. It goes from O to 300 fps in about 6 thousandths of a second, some of you can do the math and see that this is indeed lots of G's.

Yes it SEEMS that it would get torn apart or deformed by the acceleration but in reality it doesn't. The air pushes equally around the entire back of the ball. The oil inside pushes back due to the acceleration and the shell is trapped in the middle. The front of the ball does not see much pressure at all. If it did have equal pressure on it then it wouldn't accelerate!

The ball does not deform that we can see in high speed video. The video we took is at the front of the RT video mixed in with the intro. Powder a barrel for yourself and see, it's a good learning experiment.

AGD

[confedman75]

if the ball was filled fully so there were no air pockets at all would it be more air efficient since the air isnt moving the paint around to slow down the ball?

[flanders]

if there is ne paint movement with in the ball form the lev ten, there would have to be a pre existing air bubble or deformation so that spot is just being moved through the ball