Flatline Theories...

Message Topic Search Topic Options Post Reply Create New Topic Printable Version Translate Topic

 LordJovian wrote:

You're arguing about how a swallow could or could not carry a coconut.

Is that an African or European swallow?   (Sorry, couldn't resist.)

Edit:  On a more serious note; if I understand the major arguments
here, then the questions have already been answered in the following link.

This site, and other pages on it, have been referred to before, but
after reading it all the way through, I realized it answers the two
major questions being asked here.  To try to keep things
relatively straight, I will emphasize sections of quoted text in red print and any personal observations specific to the quoted sections in green print.  Now, on to the questions!

1. Does the paintball gain speed from the backspin after leaving the flatline barrel?

  No.  "Unless acted upon
by some external force (push) an object will not change its speed or
direction. We already know from experience that paintballs do all sorts
of strange things in the air. They drop; they curve. So they must be
acted on by other than forces imparted to it by the marker when in the
barrel. However, none of these forces will act to increase the speed of
the ball in the direction of motion once it leaves the marker. In other
words, the paintball is not going to magically pick up speed once it
leaves the marker. I know I keep repeating this, but for some reason
this is usually where many people seem to go wrong in their
thinking." 

2. Does the paintball from the flatline maintain speed longer once fired?

  Yes, but this could be argued.  For the sake of fairness, I
will quote all of the relevant sections and explain the conclusion I
reached based on the data presented.  

    First, a laymans definition of the Reynolds number which I found here. "The
Reynolds Number is important in analyzing any type of flow when
there is substantial velocity gradient -  shear. The Reynolds
Number
indicates the relative significance of the viscous effect compared to
the inertia effect. The Reynolds number is proportional to inertial
force divided by viscous force."  The site goes on to list the
five factors in the equation as characteristic length, velocity,
density, dynamic (absolute) viscosity, and massvelocity.  Note that actual spin (rpm) is not included anywhere in the calculation.  

    Now, the information from the paintball physics site: " Lets take 
  a closer look at one of the curves; the smooth sphere data by Achenbach is of 
  particular interest to us. The adjacent graph shows just this data and defines 
  some of the terms used to describe the Reynolds number regions. At the critical 
  Reynold number, the drag on the sphere suddenly drops by nearly a factor of 
  five. Referring back to the drag equation, this means that a ball above the 
  critical region will have reduced drag and fly further. Of course, once the 
  velocity drops below the critical Reynolds number, as we will see it must, then 
  the ball will slow down very rapidly, appearing to drop very fast (relative 
  to the horizontal distance traveled)."  Note, that this is exactly what paintballs fired from a flatline appear to do. 

      "So where does a paintball fit into this scheme. The Reynolds number
of a typical paintball with a velocity of 280 ft/sec is around 9.4 x
10⁴. From the curve, we can see that this clearly falls into
the subcritical region. As far as drag force is concerned (and perfectly
spherical paintballs), there is no free lunch for well formed
paintballs."  Note, that this appears to directly contradict my previous observation.

  First,
let me say that I believe at least part of the reason that shots from a
flatline seem to hit harder than shots fired from a normal barrel is
psychological.  As Bruce pointed out above, when people get hit
(break or not) at ranges where they can't do the same, they tend to
conclude that their opponent is firing hot.  The loudness factor
of most flatlines also probably helps to create the impression of
illegal velocities as well.  

  Second, I belive that flatlines also seem to hit harder (and have
a better chance of breaking paint at longer ranges) because of the
angle at which the ball strikes the target.  Remember that the
flat trajectory allows for direct hits at ranges where most markers can
only get glancing blows due to the arc of the round.  The paintball
physics site touched on this subject here while referring to paintball-drop testing.  "It would appear that most paintballs
will break at distances somewhere between 6 feet and 10 feet. What are
the speeds associated with these heights? Well the trajectory program
won't allow a zero velocity, but if we make the number very small and
use an angle of 0 degrees, we can obtain the speeds that the paintball
will reach just as it hits the ground. From 4 ft, 15.8 ft/s; 6 ft, 19.3
ft/s, 8ft, 22.1 ft/s; 10 ft, 24.6 ft/s. So the speeds are not very high.
Remember, we calculated that even a maximum trajectory would have a
speed of 60 ft/s as it hit the ground. However, a big factor here is the
type of surface it is hitting. 

    The above ball breakage data would appear to conflict with a comment
in another study - the "Lapco Barrel Challenge"
 by Richard Allen on barrels. This study was concerned with trying to
answer what is the best barrel. In the document, it was mentioned that
some balls were bouncing off a plywood target at 150'. I calculated the
speed that the balls should have at this distance and found it to be
around 110 ft/s. This is quite a bit different than the ~24 ft/s found
in the previous results. The difference between hitting a plywood
surface and a concrete floor should be only slight, so it is not clear
why the large difference. One possibility is that in this study the
balls were hitting the target at a glancing angle rather than
perpendicular to the surface as in the drop tests."

  Now
for the controversial part.  I concluded that paintballs from a
flatline hit harder than those fired from a regular barrel because
they do actually lose speed slower than the shots from the regular
barrel.  I base this on the following:

    Drag slows down objects that are moving on inertia only.  This is a given.
    The data above shows that at a critical Reynolds number, drag on a smooth object is reduced by nearly a factor of five.
    The data above also indicates that paintballs do not move fast enough to achieve the critical Reynolds number.
    However,
the data also describes perfectly what happens when an object slows
below that number; it appears to "slow down very rapidly", which is
exactly what happens with paintballs fired from a flatline barrel.
    I
can only conclude that a part of the equation is missing (as I pointed
out, the Reynolds equation does not take spin into account) and that if
the missing part was included, the Reynolds number would change to
match the observed behavior of the shots.

Edited by Mack