On Mythbusters last night, they tried shooting some hay at hurricane winds at a palm tree to see if the straw would peirce and pass through it. the machine they did this with was a compressed air machine with a 60 foot long barrel (this was to steady the projectiles)
The straw failed, but eventually, they tried paino wire which wnet through the palm tree (and a few other things behind the palm tree). They used high speed film so you could watch it in slow mothing.
But as I was watching, I got to thinking how is the straw/piano wire moving while inside the tube? naturally it is moving forward… but is it wabbling? even if it is flying complety straight, how many feet down the track did it become completely straightline flight? What i really wanted to see was the the slow mothing video of how the object was behaving “inside” the barrel, for the entire length. I imagine that if you used a clear tube, you could do this, and in fact may have been done. Has anyone seen video like that projectile motion inside a tube? And more to the point, something other that a round bullet, which would tumble evenly
I am not sure about your main question, I assume that the projectile would wobble like an arrow. However, the point of the 80 foot barrel was not stability but increased velocity, as they said on the show.
Sorry, I have no cite, but I do recall an explaination for this (or at least a similar) myth.
In very strong winds, telphone poles can twist violently. This can cause fine cracks on the surface to gape open, allowing straw, grass, etc to become lodged in said cracks. When the wind stops, the cracks close, with shafts of straw, etc sticking out of the pole, leading a casual observer to assume they were driven into the pole, like so many arrows, by the force of the wind.
FWIW, I pulled a length of flexible artificial rubber tubing – the stuff that’s pressed into a groove to hold screening in place – out of the turf in my parents’ backyard. It had been driven several inches into the soil beneath the grass. I had to really tug on it to pull it out.
I believe the piano wire was loaded just a couple of feet, maybe even less, from the end of the pipe. The long pipe was to compress the air and make it (and the projectiles) fly out at the highest possible speed.
They bent the palm tree, on the assumption that bending it would open up the pores (or something) in the bark (or whatever palm trees have), and shot straw at it. The results were the same.
I think Adam & Jamie were overlooking something, though. The bending and twisting of the trees is, of course, relevant, but I think the lower air pressure present in tornados and hurricanes is relevant, too. Perhaps the lower pressure causes the tree to expand somewhat, and this, combined with the bending and twisting, allow projectiles to fly further into it.
This is 87% of standard atmospheric pressure (101.325 kPa). For comparison, this is the approximate air pressure you would experience normally (i.e. not in a storm) at an altitude of 2500-3000 feet, give or take.
Secondly, I don’t think trees would expand significantly no matter how much you dropped the air pressure.
I may be misunderstanding what you’re saying here, but I don’t think this is right. The projectile was loaded at the end of the pipe next to the compression tank. That way, the projectile continued to accelerate under the force of the compressed air as it traveled the length of the pipe, reaching it’s peak speed as it exited.
Only watched it once, so my memory may be flawed, but in my head they loaded the piano wire (and darned thick it was, too) with cotton balls to make it center in the pipe–much like a dart in a blowgun. Like this (0 is cotton, - is wire):
0------0----
That way, it’s centered, and the air pressure takes the cotton and the wire along with it.