Wikipedia:Reference desk/Archives/Science/2022 April 25

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April 25

Two types of snakes.

I watch animal and zoo stories on TV. Sometimes the staff begins to handle nonvenomous snakes. Example is Indigo snakes [1]. They are absolutely docile, never bite. How does the snake "knows" that it is not venomous? I also once observed a video whereas a young keeper opened a glass door of a highly venomous snake. The snake threw its entire body toward his arm and bit him. Obviously he ended up in a hospital. How do venomous snakes "know" they are so poisonous? Thanks AboutFace 22 (talk) 00:25, 25 April 2022 (UTC)

They bite their prey. Their prey dies. They eat. Clarityfiend (talk) 02:51, 25 April 2022 (UTC)

How do you "know" you have legs? How do you "know" you have a tongue? --OuroborosCobra (talk) 03:23, 25 April 2022 (UTC)

That's proprioception. --Jayron32 12:29, 25 April 2022 (UTC)

Without getting mired in questions of animal cognition, if we think of them as bundles of habits, the bitey habits evolved (or evolved away) along with the venom glands that make the biting effective. If a black mamba had its venom glands removed, I would expect it to continue trying to envenomate anybody nearby who it was tired of, at least to begin with. Possibly it could learn not to, in time, if the experience was unsatisfactory enough.  Card Zero  (talk) 04:18, 25 April 2022 (UTC)

You might as well ask, "How does a cow 'know' that if she munches on grass it will provide her with nourishment?". If she could talk, she might say, "Gee, I didn't 'know' that. I eat it because it is yummy."  --Lambiam 07:29, 26 April 2022 (UTC)

As a former keeper of snakes, I can assure you that at least some non-venomous snakes do bite. If a snake is acting docile and not biting when it's handled, it is more likely that it is used to being handled rather than some sort of self-awareness. Venomous snakes can also be trained to put up with being handled.[[2]] --Ykraps (talk) 10:16, 26 April 2022 (UTC)

Agreed. I've been bitten by numerous non-venomous snakes (including corn snakes, king snakes, rat snakes, bull snakes, water snakes, and ball pythons) and struck at by still more. Generally those reactions have been when I was behaving in a manner that the snake would reasonably find threatening. I also noticed that even my best behaved snakes were more likely to strike a person if said person was displaying fear or nervousness. Probably because those feelings made the person do things that the snake found threatening. --User:Khajidha (talk) (contributions) 14:14, 28 April 2022 (UTC)

Bow acceleration math

I don't know if this is a math or science question. I've been asked how fast does a bow accelerate when fired. By that, the question is asking how fast does the point where the arrow is notched to the string accelerate. This is about old bows, not fancy mechanical compound bows. Is there a change in acceleration? Doing some doodling, I suspect that the point of contact between the string and arrow changes speed in a sinusoidal manner. I simplified it to a diamond and looked at the change in length of the horizontal line as you increase angle of either side. That is a sine or cosine wave (depending on how you measure it). But, bows don't have a single vertex, so my guess could be completely wrong and the only reference book we have that has good bow information is A GLossary of the Construction, Decoration, and Use of Arms and Armor by Stone. It doesn't go into much detail about how the bow works. 97.82.165.112 (talk) 14:17, 25 April 2022 (UTC)

• First, the pedantic but correct answer: the acceleration of the bow string at the moment the arrow leaves it is zero, regardless of the bow mechanics. The acceleration starts positive, and the arrow will leave whenever it becomes negative, which means at the moment it crosses zero (acceleration being a continuous function of time for all practical purposes).

Obviously, one might ask about the speed/acceleration at other moments in time, and there some physics is required. In a spherical cbow-approach, the point where the arrow is notched does move in a sinusoidal manner. More precision may be obtained by a damped harmonic oscillator model, but I don’t think we care about that.

Let x be its position in the referential attached to the bow (where x=0 is the position at rest), the position varies as $x=L\cos(ft)$ where L is the draw length and f is the frequency of oscillation (times 2π if you want to be pedantic). The maximum speed reached is then $L\times f$ (and that is when the arrow leaves the string at x=0). The maximum acceleration is $L\times f^{2}$; that is reached at x=±L.

Two random archery websites I found (one, two) give the following values: draw length L is 30 inches (0.76 m) and arrow speed (when leaving) Lf is 400 feet per second (120 m/s) for a compound bow, 200 feet per second (61 m/s) for (I assume) the more standard stuff. Taking 300 feet per second (91 m/s) so I can do the calculation in my head, the maximum acceleration is 3000 feet per square second, or roughly 900 meters per second squared. That is roughly 100 times the standard gravity (i.e. the acceleration of a falling object without air friction). Tigraan^{Click here for my talk page ("private" contact)} 15:38, 25 April 2022 (UTC)

I'm going to quibble the claim that "the arrow will leave whenever [the acceleration of the bowstring] becomes negative". The arrow is being accelerated backwards by air resistance, so it doesn't leave the string until the string's acceleration reaches a sufficiently large negative value to match that effect. --Trovatore (talk) 19:33, 26 April 2022 (UTC)

First, how dare you being such a nitpicker, and second, how dare you beat me at that game! Tigraan^{Click here for my talk page ("private" contact)} 15:58, 27 April 2022 (UTC)

This site points out that speed claculations (such as those quoted above) usually assume a standard draw weight of 70 pounds (32 kg) and an arrow weight of 350 grains (22.6 grams). Bows, of course, come in a great variety of draw weights, youth training bows for example, are often only 15 lbs. Alansplodge (talk) 19:03, 26 April 2022 (UTC)

Thank you for the references. They are primarily about calculating arrow speed rather than acceleration, but it does appear that it is pretty much a sinusoidal acceleration. Initially, the arrow accelerates very slowly. The acceleration increases throughout the time that the arrow is fired. I doubt the inventors knew it at the time, but this action ensures that the arrow remains notched because the string is constantly pushing faster against it. 97.82.165.112 (talk) 10:19, 27 April 2022 (UTC)

See also Jerk (physics). {The poster formerly known as 87.81.230.195} 90.208.88.97 (talk) 12:33, 27 April 2022 (UTC)

Thanks. That got me to a reference, "On the of the Bow and Arrow," a thesis by Kooi. 97.82.165.112 (talk) 12:58, 27 April 2022 (UTC)