I think I blogged before that I am part Native American, but there is more to it than that. It turns out that one of cousins is about the best arrowhead napper in the USA. I am not sure how he got into arrowhead making or how he got so good. To most, they would say that arrowhead making is an art handed down generation by generation. I used to find a lot of arrowheads when I was out in the fields, but not too much anymore. Most were made for Obsidian or volcanic glass. They were black and very sharp. I don't think Native Americans made arrowheads just to have them get lost, so the fact that we still find so many when working our fields, means they must have made millions and used them for hunting for thousands of years. Consider a one acre field of about 40,000 square feet, to find 5 arrowheads in that one field would mean that the Native American would have to have lost how many per year? Figure that if you found 5 that here must have been at least 3 or 4 time that number lost in the field, or 20. Now consider that this Native American hunted this field for 20,000 years. To lose 20 arrowheads, he would have had to lose one every 1,000 years. Hey, Native Americans have been here a very long time. Now onto physics.
The procedure for making an arrowhead is to first find a good piece of stone or flint. These are types of stone that are very dense and when cracked result in holding sharp edges. I am not going to go into the stone much here. I am more interested in the process and physics associated with that. The way that the arrowhead is formed is to hit it with another stone in such a way as to chip of small flakes. There is another way that uses pressure to flake off stone, but I am not going there either. I am only going hitting one stone against the other since this is the oldest method us humans used.
A few basic points about stone. It is very brittle. What does that mean? It has a very high modulus of elasticity. This means that it is very stiff. If it were considered a spring, it would be one of stiffest springs in the world. If you hit a stone with a hammer, the hammer will deflect more than the stone. That is why in arrow head making you use a stone to hit a stone. From here on it will be about F=MA or force = mass time acceleration. This equation give you clue about how to flake an arrowhead. We need a high force and we only acceleration to work with, but in this case, it is deceleration that we need. In one hand we hold the arrowhead and in the other we have the striking stone. The mass we are talking about is the mass of the arrowhead. The striking stone is much larger than the arrowhead. The energy in the striking stone is a function its mass and its velocity. When the striking stone hits the arrowhead, it tries to move or accelerate the arrowhead. The mass of the arrowhead resists the acceleration and a force "F" is place on the arrowhead and the striking stone at the point where the striking stone hits the arrowhead.
A couple of fine points. It is the mass of the arrowhead that affects to force. This means that for larger arrowheads, the speed of the striking stone can be less. When the arrowhead gets very small and has less mass, the speed of the striking stone has to increase to generate a force large enough to flake of a chip. Further, the arrowhead can not be placed in a vice or other stiff holders or the arrowhead will be crushed. It has to be free to move a slight amount so that the holding forces can be equalized. Normally the napper used a small piece of leather to hold the arrowhead.
These are the basic physical principles and it now shifts to art where accuracy and speed count. The vector of the force is equally important. It needs to be a glancing blow that places the force parallel to the surface of the arrowhead, but to actually have a force, the blow needs to have a vector component that is normal or directly into the arrowhead so that enough contact friction can be generated to develop the force parallel to flake off a chip. It is complicated, but the rules of simple physics still apply. If a bullet was shot into a big rock at an angle, it would not split the rock, but only flake off some chips. If on the other hand a big rock, the same size as the rock being hit was used, it could split the rock even though the rocks hit together at much lower speeds. I think you can see why speed is so important. You can't make an arrowhead with slow swings of the striking stone, but you could smash you arrowhead.
I know this is not the best presentation of how physics applies to arrowhead making, but I think it is a start and may get you to thinking.
