Stone projectile points represent the single most durable
artifact occurring in the archaeological record. An enormous amount of research
and speculation have gone into their interpretation. Materials and knapping
techniques have been studied, point styles have been typed, categorized, and
dated, and volumes of information have been published which relate directly and
indirectly to stone projectile points. However, other than explaining that
notching and fluting represent a hafting technique, and the sharp edges and tip
are for inflicting traumatic wounds, their function and effects as a mass within
the mechanical systems of the bow-and-arrow and atlatl-and-dart have been
largely ignored.
The primary motivation behind advances in projectile technology is to make a
smaller particle go faster. Higher velocities generate flatter trajectories,
promoting greater accuracy. Velocity influences the kinetic energy of a particle
to a greater degree than does its mass. In the mathematical expression for
energy, one half the mass of a particle multiplied by the velocity squared, it
can be readily seen that velocity plays a more significant role in increasing
the energy of a particle than does mass. Over time, progressively lighter
particles attaining higher velocities: spear, dart, arrow, bullet, have marked
advancements in projectile technology. However important the velocity of a
particle when analyzing a weapons system, the mass of that projectile, how that
projectile is accelerated, and it's effects upon the mechanics of the system,
are paramount in the interpretation of that weapons system.
Prehistorically, the concept of making smaller projectiles travel faster can be
generally traced in the study of stone projectile points, with heavier points
generally occurring earlier and lighter points occurring more recently in the
archaeological record. Studies of stone points from sites known to have utilized
either atlatl-and-dart or bow-and-arrow systems have shown a trend toward
lighter points for arrows (3 grams or less) and heavier points for darts (4
grams and greater).
Generally speaking, the atlatl predates the bow by a considerable margin, and,
in fact, the atlatl has enjoyed such an extended and widespread tradition that,
comparatively speaking, the bow-and-arrow can be seen as a recent development in
projectile technology. In North America, the atlatl can be traced back in the
archaeological record some 8 to 10 thousand years, whereas the bow is generally
accepted as having been introduced only 1,500 to 2,000 years ago. It is true
that the atlatl-and-dart was used in North America longer than any other weapons
system to date. Therefore, a detailed study of the projectile point mass, and
it's effects on this system, establishing parameters for minimum and maximum
mass will help, through a process of elimination, to distinguish between arrow,
dart, and lance points.
TOOL TRADITIONS
Projectile point types are primarily identified by style. Size, material, and
knapping techniques are noted to a lesser degree, but mass generally not at all.
The stated diagnostic for the various types is hafting technique. Indeed, this
seems to be the case because of the variety of notched, stemmed, and fluted
points found. Hafting technique certainly played a role in certain styles of
points and the similarity between the points of a particular tool tradition.
But, as the primary function, hafting technique falls short when considering the
point as part of a mechanical system.
What can be seen in the similarities among the points of a tool tradition, when
considering the point as part of a mechanical system, is production-line
consistency. Keeping in mind that a highly sophisticated weapons system is
literally behind the projectile points of a particular tool tradition lends an
entirely new perspective to the interpretation of stone projectile point
attributes. For a weapons system of any degree of sophistication, consistency in
the manufacture of its various components is paramount for the success of its
deployment.
During a study of atlatls and related artifacts at the Smithsonian Institution
in Washington, D.C., a collection from a site in South Dakota was examined. The
collection contained two or three atlatl weights, which were of primary
interest. From the same site were several projectile points and performs. Three
of the points appeared to be new and unused with no indication of resharpening.
Two of these points were made from what appeared to be the outer cortex of
chert, the third was of Knife River Flint, an extremely dense, hard material.
The width, thickness, and notching of all three points were approximately the
same. However, the length of the Knife River Flint point was a full centimeter
shorter than the other two. In testing the mass of the points on a digital
scale, allthree projectile points were found to weigh essentially the same at
7.6, 7.7, and 7.8 grams, respectively. This suggests that the consistency of
mass for stone points was an important consideration in the manufacture of the
projectile points within a tool tradition. Because width, thickness, and
notching were also approximately the same, a secondary importance to these
dimensions is noted. However, it would appear length is adjusted from material
type to material type in order to keep mass consistent, thus standardizing the
projectile points of a tool tradition. These results were supported during a
study of bannerstones at the Field Museum in Chicago. Multiple examples of
points tested showed a definite pattern of mass consistency within a tool
tradition. The similarities between points within a tool tradition can be seen,
not primarily as a hafting technique but rather an attempt to optimize a weapon
systems mechanical efficiency threw standardization of mass. Also, stone was not
predominately used in the manufacture of projectile points because of its
durability, convenience, or it's ability to pierce hide and flesh.
Other materials such as bone, antler, and just an old-fashioned pointy stick
work just as well. Stone possesses one advantage over these other materials:
density, concentrated mass. Projectile points made from other materials can be
made to have the same mass as a stone point, but they would be larger, less
efficient and, therefore, less desirable than stone.
FLEXABLE SHAFT MECHANICS
Both the bow and the atlatl accelerate a flexible shaft from the rear and are
therefore defined as flexible shaft accelerators. The arrow and dart are defined
as the flexible shafts under acceleration. The flexible shaft stores and
releases spring energy used to accelerate away from a launching platform. When a
flexible shaft is accelerated, the point mass at the opposite end resists that
acceleration and causes the shaft to flex and compress, storing spring energy to
be used for the launch. Point mass plays a critical roll in the amount and rate
at which energy is stored and released.
Under acceleration from the rear a flexible shaft cycles threw a series of
harmonic isolations propagating transverse waves. The period of oscillation, the
time it takes the shaft to complete one cycle, is the same whether the force
imparted is large or small. Changing the length, flex, or point mass alters the
period of isolation for a given shaft. This alters the actual launching point of
the shaft: when the shaft pushes itself away from its launching platform and
separates to travel down range. Timing is critical and needs careful
consideration in the mechanics of flexible shaft acceleration.
The difference between the bow and atlatl lies in the type of acceleration
applied by each. The bow is a linear accelerator, accelerating a flexible shaft
in a straight line. The atlatl is an angular accelerator, accelerating a
flexible shaft in an arc. In the atlatl system, the dart itself is the single
most important component. Mechanically, the dart acts like a long spring. When
accelerated by the atlatl, it flexes and pushes itself away from the atlatl
spur, launching smoothly and effectively. The mass of the projectile point acts
upon the system by resisting that acceleration and causing an "efficient"
compression of the dart's spring.
In order for the mechanics of the atlatl-and- dart system to function, the dart
must be flexible. The flexible shaft is the mechanical foundation of this
system, and the point mass plays a critical role within it by causing the shaft
to flex and store spring energy.
In the bow system the arrow functions exactly the same. The arrow is accelerated
from the rear by the bow's string. The arrow flexes and stores spring energy to
push itself off the bowstring at launch. The point mass influences the amount
and rate energy is stored and released. This suggests a closer relationship
between these weapons than previously recognized. The physics and mathematics
describing the arrow and dart are exactly the same. Only the constants in the
mathematical formulas are different. The relationship suggests that the
bow-and-arrow is not the novel invention it is thought to be, but rather a
progression of existing technology. The bow did not replace the atlatl, the bow
evolved from the atlatl.
The potential energy available to a given flexible shaft is dependent upon three
things: the length and flexibility of the shaft itself and the mass of the
projectile point at the business end. The mass of the point directly controls
the amount and rate at which energy is available to the system. Without proper
point mass, the system will not function to it's full potential. Mechanically
the flexible shaft is defined as a spring-mass system. A mass is required for
efficient operation.
Foreshafts were developed to help maintain the precise working relationship of
length, flexibility, and point mass. Considerable effort went into manufacturing
a properly tuned, flexible shaft. When launched downrange, the chances are
likely that the stone point will break upon impact. Sometimes, the breakage can
be repaired with acceptable loss of mass, still within functioning parameters.
But, if the point snaps and takes part of the heft with it, a one-piece shaft
would be shortened considerably when a new point was rehafted onto it. This
system is so sensitive that changing the length of the shaft by 1 inch or 1
centimeter changes the mechanics of the system causing the shaft to launch
earlier, thus changing its point of impact on a target. A shorter shaft is a
stiffer shaft, but, with the advent of foreshafts, this problem was completely
avoided. When a point broke it was replaced as easily as a new bullet is
replaced in a gun today.
MINIMUM POINT MASS
The mass of stone projectile points must be more carefully considered in order
to gain a more complete understanding of the weapon system they represent. As
stated, the atlatl-and-dart system is a deceptively complex mechanical system
and the point mass is an integral part of that system. The lighter the point,
the more sophisticated the system. There are limits to the minimum mass that can
function in the system. Part of this minimum limit has to do with the materials
from which the dart is manufactured. The less dense the dart material, keeping
in mind the parameters of length and flexibility, the lighter the point mass
that can be successfully used on a dart of that material. Experiments with
several types of dart material have found that, "locally" (Gallatin Valley,
Montana), red osier dogwood is best. With this material, a dart with a minimum
point mass of approximately 5 g can be designed for peak performance. Because
the density of red osier is .6 kg/L, the lighter the projectile point, the less
influence it has on this material. Dart materials of lesser density, such as
cedar, can be designed to function efficiently with lighter point masses. A
cedar dart can be designed to function efficiently with a point mass of 3 grams.
This dart would be approximately 54 inches in length, and functioned well with
an 18 to 20-inch atlatl having an effective range of 20 to 25 yd. Beyond this
minimum, designing a dart that will function effectively with a less than 3-g
point mass is not efficient. Due to the limits of the acceleration available to
the system, as the dart shortens, the effective range of the system also
shortens in order to maintain the proper timing match between atlatl and dart.
Also, because the acceleration is angular rather than linear, less velocity is
achieved by shorter atlatls that are required to function with shorter darts.
There is also effective mass to be considered. This is the mass of the point
after it has been hefted onto a shaft. Experiments conducted in hafting stone
points found that the glue, sinew bindings, and the surrounding wood of the
notch itself add an average of 1 g to the overall mass of a dart point. Arrow
points were not tested but some increases in mass can be expected. In effect, a
2.5 gram point may have the effective mass of 3.5 grams. Is it a dart point or
an arrow point? In order for a lighter point to function effectively in a
flexible shaft system the acceleration must be drastically increased. This is
where the bow came in.
MAXIMUM POINT MASS
In considering what is the maximum point mass that can be tolerated in the
atlatl and dart system, all aspects of what were considered for minimum point
mass are reversed. With greater point mass goes greater dart and atlatl length.
The Aborigines of Australia are known to use darts up to 12 feet in length with
correspondingly long atlatls of more than 3 feet in length. Although no
opportunity to directly weigh any Australian dart points presented itself during
museum study, many were observed hafted to extremely long darts in the
Smithsonian collections. They were quite large and certainly in excess of 30
grams. Atlatl-and-dart systems of this massive design are far less efficient
than the more reasonable North American dimensions. In experiments of dart
design lengths in excess of 8 ft. point mass becomes less critical for efficient
operation due to the leading mass of the dart material itself helping in
compression along the entire length of the dart. Indeed, some Australian darts
had no point mass at all and did not appear to be designed for any. So long as a
dart is sufficiently flexible, extreme length lessons the sensitivity of an
influencing point mass. Australian atlatl systems appear to represent an
extremely basic technology, one that is a step or two above a hand thrown spear.
They conform to the basic definition of an atlatl and dart system since the dart
is flexible and uses spring energy to launch itself away from the atlatl. A
basic knowledge of timing is also apparent in Australian atlatl design. The
lengths of the darts are generally three times that of the atlatl. In theory
this relationship works out to p times the length of the atlatl as measured from
the middle of the grip to the tip of the spur. Clovis and Folsom tool traditions
may have used systems of a similar
technological level.
The question of what is the maximum allowable point mass for efficient operation
of the atlatl-and-dart system is much less defined than is the minimum mass.
Minimum mass can certainly go down to a precise 3 grams. Maximum mass however
can be as much as 20 to 30grams, and, of course, the greater the design mass,
the greater the deviation in that mass that can be tolerated in the system for
efficient operation. This may result in the stone points of an early tool
tradition varying in mass by as much as 10 grams or better
Stone projectile points represent the single most durable artifact occurring in
the archaeological record. An enormous amount of research and speculation have
gone into their interpretation. Materials and knapping techniques have been
studied, point styles have been typed, categorized, and dated, and volumes of
information have been published which relate directly and indirectly to stone
projectile points. However, other than explaining that notching and fluting
represent a hafting technique, and the sharp edges and tip are for inflicting
traumatic wounds, their function and effects as a mass within the mechanical
systems of the bow-and-arrow and atlatl-and-dart have been largely ignored.
The primary motivation behind advances in projectile technology is to make a
smaller particle go faster. Higher velocities generate flatter trajectories,
promoting greater accuracy. Velocity influences the kinetic energy of a particle
to a greater degree than does its mass. In the mathematical expression for
energy, one half the mass of a particle multiplied by the velocity squared, it
can be readily seen that velocity plays a more significant role in increasing
the energy of a particle than does mass. Over time, progressively lighter
particles attaining higher velocities: spear, dart, arrow, bullet, have marked
advancements in projectile technology. However important the velocity of a
particle when analyzing a weapons system, the mass of that projectile, how that
projectile is accelerated, and it's effects upon the mechanics of the system,
are paramount in the interpretation of that weapons system.
Prehistorically, the concept of making smaller projectiles travel faster can be
generally traced in the study of stone projectile points, with heavier points
generally occurring earlier and lighter points occurring more recently in the
archaeological record. Studies of stone points from sites known to have utilized
either atlatl-and-dart or bow-and-arrow systems have shown a trend toward
lighter points for arrows (3 grams or less) and heavier points for darts (4
grams and greater). Generally speaking, the atlatl predates the bow by a
considerable margin, and, in fact, the atlatl has enjoyed such an extended and
widespread tradition that, comparatively speaking, the bow-and-arrow can be seen
as a recent development in projectile technology. In North America, the atlatl
can be traced back in the archaeological record some 8 to 10 thousand years,
whereas the bow is generally accepted as having been introduced only 1,500 to
2,000 years ago. It is true that the atlatl-and-dart was used in North America
longer than any other weapons system to date. Therefore, a detailed study of the
projectile point mass, and it's effects on this system, establishing parameters
for minimum and maximum mass will help, through a process of elimination, to
distinguish between arrow, dart, and lance points.
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