Hmm why do paintball hits leave RING welts??

[AGD]

Got to love this forum! Someone asks about breaking paintballs and we get into structural design.

AGD

[shades]

BLOOD!!!!

The dome shape of the paint ball forces the blood in the impact area from the center of ground zero to the outside edges of the paintball dia. causing the capillaries on the outside dia. to hemorrage(bleed/leak/break)leaving the inner portion of the impact area strangely pale for awhile, due to the blood that was forced out. Hence a RING is born! Then whole area of impact may or may not bruise depending on how much capillary damage was done and where the hit occured. Either giving you a RING bruise or a BIG *SS one. Im sure angle of impact figures in, relating to the shearing forces on the skin and capillaries. You will normally get more bruising over soft tissue areas than over bones where the shell of the ball is more likely to break the skin. Example: The knuckles of the hand. Ouch! But hardly a bruise. But of course this how I look at things because I am a R.N.
BTW I believe its the velocity of the paint in the ball that causes the ball to break not the impact of the shell, otherwise it would bounce off of you like a ping pong ball or a super ball. So, to those people want to freeze their paint to hurt someone, sure it will hurt but you will never tag any one out.

[lamby]

the sphere/triangle debate is nice, but...

The strongest shape with equal mass is the the cylinder and neither of the above.

This is due to the physics that was mentioned above.

1.) a triangle (we will use cone because of the 3d aspects are equal) will generate force on an edge (the base or the tip which ever is the weakest)that is fixed to a point but dispersed over a larger area than say a rectangle of equal mass.

2) A sphere is incredibly strong as it can displace load over its conplete area (that is if the area is placed over the complete area) a paintball hit is generating all of the force at a minute point of impact, therefore crushing the leading edge of the ball.. Remember there is equal force around the back side of the ball in flight minus turbulance.

3.) when the leading edge of the ball collapses you get a doughnut pattern because the trailing edge is the last to compress before rupture stress is generated. This then creates a very strong pattern that would most ressemble a thick cylinder (which has the GREATEST vertical ridgity). at breaking point, the mass of the paint is expelled outward into this "doughnut" (I think the correct name for this shape is a toride, but I am not sure and I am not in the mood to surf for it... so look it up if you want )

This is the reason for the circular bruises. The force is in a circular pattern.

This is what VALCONE said, but with more correct geometry and physics added into the mix...

Just to confuse yall even more.

[hitech]

A couple of things.

First, remember that not all materials break apart in the same manner. I do not believe that Perfect Circle Paintballs leave a circular welt.

Second, when determining what shape is the strongest you have to consider what forces it will be resisting. A cylinder is not the strongest when the force is applied to an small point on it's "side". The same is generally true with most shapes that have a side. It all depends on where/what type of force is being applied. That's why we see different shapes being used in different applications.

[lamby]

listen to hitech... In his words there is wisdom.

He is correct on every point

[SlartyBartFast]

Originally posted by lamby
the sphere/triangle debate is nice, but...
{...}
Just to confuse yall even more.

But you've added two different variables to the mix. Is the shape a solid and is it 2d or 3d.

The strongest 3d solid if I remember correctly is a sphere. :P

In 2d or considering planar forces, triangles win out.

I won't discount I could be wrong. It's been a while since I've sat in a classroom.

[Redkey]

more drivel

Shades... interesting. I never thought of it from a "hydrostatic shock to the body" standpoint. It's probably some combination of the two events.


Lamby...

1. Not sure I follow this, could you please elaborate?

2. What do you mean by equal force on the back side of the ball during flight? If the forces on the front and the back of the ball are equal then the ball isn't moving. Perhaps I just missed something.

3. Leading edge compressing to create a toroid? Trailing edge last to compress before rupture stress? Do you have time to sketch this out? I've having a hard time visualizing the effect(s) you are describing.

Thanks

[lamby]

Re: more drivel

[QUOTE]Originally posted by Redkey
[B]
Lamby...

2. What do you mean by equal force on the back side of the ball during flight? If the forces on the front and the back of the ball are equal then the ball isn't moving. Perhaps I just missed something.

All right, let me see if I can make this a little easier to follow... The paintball will have two phases of travel in its flight: acceleration, and deceleration.

1. Acceleration is the the act of making the ball overcome the enertial forces that are keeping it still.. IE friction of the breech and gravity. (this is done by firing the marker)

2. Deceleration is every point after the maximum acceration velocity is achieved. Once the paintball has reached maximum velocity, only two factors will slow it down. 1) aerodynamics (in the air) and 2) friction (air, object, skin, ect).

Now this is where it gets more confusing, since only those factors are going to effect the distance the ball will travel before it will slow down. you will have to look at the physical makeup of the ball as opposed to the resistance (friction) that is enacted upon it. (where does it hit? a sup-air bunker will prob deflect the ball, where as a brick wall will not.)The reason the paintball disforms is due to the fact that it was designed to "give" before skin will.

So, you take a paintball that is past its acceration phase.. there is now an even pressure behind the ball.. ( which is slightly below atmospheric pressure - minus turbulance) and a resistance to the front of the ball caused by the movement of air across the surface of the paintball.

When this paintball hits an object like your skin. The first part of the ball to contact you will have a MUCH greater force of resistance (friction) than the rest of the sphere has acting upon it. This is not the point that is suffering the greatest amount of stress. But since the paintball is not a true solid there is give designed into the shell and its contents. The shell at the leading edge will start to compress. this forces the paint inside to move out of the space that it was currently occupying. It will move back and to the sides (there is no where else for it to go).

As the ball continues forward tring to push itself into the resistive object (your skin). Structial integrety of the object is being comprimised. The paint that was pushed to the outside and back of the sphere still needs to travel somewhere as the ball continues to compress. now the back of the ball will start to colapse (just like the front) because the structure is stronger on the outside of a half circle than the middle.

This will push more paint into the outside of the shell. There is some point when the shell can no longer withstain the pressures that are building up inside of it colapsing self and ruptures. This will then allow the trailing edge of the pall to continue its compression because now there is very little resistance to over come until it compresses into the leading edge.

What you will have at one point is a ball that has a good majority of its mass of the outside of the sphere. the point with the then greatest structual strength. Thus why even if you gog someone you still get the circular rings (look at your goggles you might see some of the same rings you get as welts)

3. Leading edge compressing to create a toroid? Trailing edge last to compress before rupture stress? Do you have time to sketch this out? I've having a hard time visualizing the effect(s) you are describing.

I will do a photoshop version if I have time (which I dont today.) the best even though greatly exagerated view would be a picture of a red blood cell.

Well, this answer was definately longer than I wanted it to be.... :)

Thanks

[Viddles]

The arch is a strong structure but not the strongest. The arch spreads the downward force out across the whole arch ultimately depending on the bases to be held in place. As long as the base of the arch is secure, the arch will be sturdy. However, you have to depend on something to hold the base, so it isn't strong on its own.

A sphere on the other hand is very weak. When pressure is applied to any part of it, the sphere will give, and lose shape/collapse. If you push down on the top of a sphere, the top half or upper hemisphere distributes the force outward from the center of the sphere. However, the bottom half of the hemisphere does NOT keep the walls of the sphere from collapsing outwards. Instead, the shape pancakes. It's pretty much the weakest 3 dimensional object.

The strongest structure is a four sided object made of equilateral triangles(3 sided pyramid). The triangular design won't shift like a box. (ignore the dots in the following shapes as this board doesn't recognize blank spaces. Without the dots/periods the characters used to make the objects would just be bunched together forward and backward slashes)
..______
./......../
/_____/ <---see box shift:)

The weakest areas on a triagular object are obviously the midpoint of any side. By simply putting another triangle inside of that triangle you strengthen that point.
...../.\
..../...\
.../___\
../.\..../\
./...\../..\
/___\/___\ <----woah, it's the tri-force

With repeating the triangle inside of triangle inside of triangle design infinately, you theoretically have an uncollapseable object because every time there is a weak point(midpoint) a new triangle is there to re-enforce it.

As far as the ring for a bruise, my theory is that when the edge of the paintball first hits you, the paint inside the sphere is driven outward towards the walls of the paintball(see above about the sphere). Once it is against the wall of the paintball it has nowhere else to move. That means that a large part of the mass is against the wall of the ball in a ring shape as it slams into you. The brunt of the force is a ring of paint. Granted it, this is just my "theory", or rather hypothesis as I have not tested this in any way.

[Person]

Re: BLOOD!!!!

Originally posted by shades
The dome shape of the paint ball forces the blood in the impact area from the center of ground zero to the outside edges of the paintball dia. causing the capillaries on the outside dia. to hemorrage(bleed/leak/break)leaving the inner portion of the impact area strangely pale for awhile, due to the blood that was forced out. Hence a RING is born! Then whole area of impact may or may not bruise depending on how much capillary damage was done and where the hit occured. Either giving you a RING bruise or a BIG *SS one. Im sure angle of impact figures in, relating to the shearing forces on the skin and capillaries. You will normally get more bruising over soft tissue areas than over bones where the shell of the ball is more likely to break the skin. Example: The knuckles of the hand. Ouch! But hardly a bruise. But of course this how I look at things because I am a R.N.
BTW I believe its the velocity of the paint in the ball that causes the ball to break not the impact of the shell, otherwise it would bounce off of you like a ping pong ball or a super ball. So, to those people want to freeze their paint to hurt someone, sure it will hurt but you will never tag any one out.

I agree with the part that the impact forces the blood out to the edges. excellent