Wikipedia:Reference desk/Archives/Science/2021 February 9

= February 9 =

How can a ball of glass bounce higher than rubber ball?
How can a ball of glass bounce higher than rubber ball? I always thought reverse would happen. Rizosome (talk) 02:42, 9 February 2021 (UTC)
 * It might depend on what it's bouncing off of. Where did you see this? ←Baseball Bugs What's up, Doc? carrots→ 02:59, 9 February 2021 (UTC)
 * Doesn't matter where they saw it. It's a common demonstration. And you could easily try it yourself. ApLundell (talk) 06:33, 9 February 2021 (UTC)
 * How would dropping them both on concrete work out? ←Baseball Bugs What's up, Doc? carrots→ 07:05, 9 February 2021 (UTC)
 * Probably not catastrophic, if that's what you're thinking of? Haven't you ever played with glass marbles? They'll bounce on concrete real nice. ApLundell (talk) 07:24, 9 February 2021 (UTC)
 * I don't recall trying to bounce them on the sidewalk. In any case, you've answered the OP's questions, and mine. Thank you! ←Baseball Bugs What's up, Doc? carrots→ 10:52, 9 February 2021 (UTC)
 * It would be interesting to test against a Super Ball. ←Baseball Bugs What's up, Doc? carrots→ 10:55, 9 February 2021 (UTC)
 * The rubber flexes and absorbs some of the energy.
 * A glass or steel ball will not, and so it will bounce higher than most types of rubber. here is an article that discusses it.
 * (Obviously, there are limits. Throw a glass ball hard enough and it will absorb the energy by shattering into a zillion pieces!)
 * ApLundell (talk) 06:33, 9 February 2021 (UTC)
 * Roughly speaking, the squishier the material, the more energy it absorbs on collision. A balloon filled with sand will not, or hardly, bounce. The energy loss is expressed by the coefficient of restitution, which is higher for glass than for rubber; see the section Colliding different materials and practical measurement. See also the articles Bouncing ball (for the physics) and Bouncy ball (for the material aspects). Squishiness is not the sole determining factor, as demonstrated by Super Balls, which are squishier than glass marbles but have a higher coefficient of restitution, about 0.85 (bouncing off concrete). A glass marble gets to only about 0.66, so the Super Ball is the higher bouncer. --Lambiam 11:12, 9 February 2021 (UTC)
 * I copied your question into the Google search-bar and hey presto (second result): Why a Glass Ball Bounces Higher Than a Rubber Ball. Alansplodge (talk) 11:43, 9 February 2021 (UTC)
 * I think another good resource for explaining this, in addition to those above, is elastic collision vs inelastic collision. In an elastic collision, all of the kinetic energy is conserved, so if a bouncing ball hit the Earth elastically, it would bounce back up with the same kinetic energy, and so would reach the same height no matter how many times it bounced (all other things being equal, such as the Earth being stationary for the purposes of this reference frame, zero air resistance, etc.). However, real bouncing balls don't actually bounce elastically, rather, they bounce inelastically. The total kinetic energy is not conserved, it is lost as some of it is converted to other forms of energy. As a result, each time a ball bounces, it has less kinetic energy than it started with before the bounce, and cannot reach the same height. A glass ball is more elastic than a rubber ball. Note that I am using the word "elastic" as it is used in physics, and not as it is used colloquially. I find very interesting how colloquial usage of terms often runs nearly opposite to their scientific usage. A rubber band is something we think of as elastic, but when a rubber ball bounces, it is further from an elastic collision than a glass ball, and we don't think of a glass ball as "elastic". --OuroborosCobra (talk) 00:37, 10 February 2021 (UTC)

M's butterfly collection
I've recently watched On Her Majesty's Secret Service, and I have one thing to say and one thing to ask about M's butterfly collection (which is briefly shown at about 44 minutes into the movie): first of all, I'm pleased that none of them frightened me (because none had an appearance, and especially a color pattern, similar to that of Papilio glaucus or P. garamas); and second of all, does anyone happen to know what are the species of those pretty little (or not so little) critters? Because I couldn't positively identify any of them (except the one on the far right, which Bond identified as an unusually small Nymphalis polychloros, although it might just as well have been its smaller cousin), except that the orange one on the middle left looks like some kind of fritillary (don't know the species, though), and the black one with hindwing spurs on the lower right looks similar to the male Papilio polyxenes (but I know it can't be, because it doesn't have that bold yellow band on the trailing edge). Can anyone identify any of these species? 2601:646:8A01:B180:714F:5D88:96DA:F4B4 (talk) 12:53, 9 February 2021 (UTC)
 * I'm curious to know why you find those 2 species scary-looking. ←Baseball Bugs What's up, Doc? carrots→ 14:32, 9 February 2021 (UTC)
 * I don't know if it's the same user or not, but there was a semi-frequent refdesk IP-user that had a severe butterfly phobia. I had a room-mate in university who also got freaked out by them. Phobias are weird things. Matt Deres (talk) 15:13, 9 February 2021 (UTC)
 * That does sound vaguely familiar. In any case, I wonder if it's connected with Trypophobia in some way. ←Baseball Bugs What's up, Doc? carrots→ 16:07, 9 February 2021 (UTC)
 * Lepidopterophobia is a thing. Pity Vladimir Nabokov never wrote a novel about a person with a butterfly phobia. --  Jack of Oz   [pleasantries]  21:21, 9 February 2021 (UTC)
 * Which redirects to Entomophobia. I can see having some fear (or at least a very healthy respect) concerning bees or ants. But are there any venomous butterflies or moths? ←Baseball Bugs What's up, Doc? carrots→ 00:25, 10 February 2021 (UTC)
 * To the knowledge of this former amateur lepidopterist, no adults are, although a few species of caterpillars have irritant hairs or are poisonous if eaten. However, part of the definition of Specific phobias including Zoophobias is that they are irrational, and may stem from experiences in early childhood. My late grandmother had a phobia about kittens. {The poster formerly known as 87.81.230.195} 2.125.74.203 (talk) 07:13, 10 February 2021 (UTC)
 * Regarding my phobia of those 2 species (and all others which look like them): yes, I am the same user who had previously reported a severe phobia of swallowtail butterflies -- but based on my original research over the past 2-3 years, I can now be more precise and say that I have a phobia of only tiger-striped (or zebra-striped, like Protographium marcellus) swallowtails (and then only those with a perceived size bigger than about 3-3 1/4 inches, so for example Papilio canadensis and P. zelicaon are too small to scare me, and P. machaon can only scare me at near-maximum size), or species which are exceptionally large (such as P. cresphontes), but not solid black ones of reasonable size like P. troilus (which I actually kind of like, as a matter of fact). In other words, it's not the tails -- it's the size and the stripes!  As for why, who knows -- maybe a butterfly with a similar appearance snapped its wings open at me when I was too young to remember (probably a N. polychloros -- they do that and they're pretty big, and the only swallowtail native to where I lived then was P. machaon, which does not do that), or maybe I had a close encounter with a P. multicaudata and was so terrified by its yuge size that I began to fear all butterflies with a similar appearance (I remember when I first saw a tiger swallowtail, which I think was a P. rutulus based on its size, I was not any more fearful of it than I was of any other large butterfly at the time -- that is, since it was some distance away, I was apprehensive but not acutely frightened -- it was only later that tiger swallowtails became especially scary for me).  Anyway, that's not what the question was originally about, was it? 2601:646:8A01:B180:B17C:FCE8:58C0:4A1 (talk) 02:27, 11 February 2021 (UTC)
 * Thanks for explaining. And note that you brought it up. ←Baseball Bugs What's up, Doc? carrots→ 13:06, 11 February 2021 (UTC)


 * A rather foggy YouTube clip of M's collection is here. Alansplodge (talk) 19:13, 9 February 2021 (UTC)