Wikipedia:Reference desk/Archives/Science/2017 November 20

= November 20 =

How hard can ice be?
A plastic bag containing a 3 to 4 kg chunk of ice fell of a table and cracked a terracotta floor tile. The ice showed almost no damage. Was the tile substandard or can ice really be harder than terracotta? The ice temperature was estimated at about -10 to -15 Celcius. It was frozen in a walk-in freezer at a meat packing plant set to -20C. Roger (Dodger67) (talk) 17:14, 20 November 2017 (UTC)
 * There's much more at work here than merely "hardness"; among other things, there is also the shape of the two pieces and the manner of impact. If you hold up a piece of aluminum foil, you can deform it with a cotton ball or feather, but you wouldn't normally say that either of them were "harder than" aluminum. Consider also that there probably were small cracks in the ice, but these essentially can "heal" if they don't immediately result in fracture. Matt Deres (talk) 17:38, 20 November 2017 (UTC)


 * The temptation is to answer this question by referencing the famous Mohs scale of mineral hardness, where ice is a 2 and terracotta is usually closer to a 5. But that's not the kind of "hardness" we're looking for here. It just means that terracotta will easily scratch a piece of ice, while ice will not easily scratch terracotta, which I think we knew.
 * We're really looking for a measure of material strength. Probably either Toughness or Fracture toughness.
 * I don't have an exact answer for you, but check out this mystifying chart.
 * If I'm reading it correctly, terracotta, being a porous non-industrial ceramic, should be tougher than ice, but not a lot tougher.
 * So why did your tile break but not the ice? Probably luck. Ice could certainly be heavy enough to smash tile. The mystery is really only why the tile broke first. That probably comes down to how they landed. Whether there was a pressure point or a weak spot, etc. (Also, Are you sure the ice was undamaged? If a chip came out of the ice at high speed it could absorb a lot of the energy.)
 * I don't think anyone can give you an exact mathematical answer without about a bunch of measurements and stuff. Sorry. ApLundell (talk) 17:39, 20 November 2017 (UTC)
 * Per ApLundell, there are different measures of hardness, it's a vague term and asking how "hard" something is depends on what you mean by hardness. None of these, however, strictly applies to the scenario being described.  One can break a steel container with nothing but the force of air pressure, and yet air is not "hard" by any definition.  The relevent thing here is not how "hard" the ice is, per se, but with how much force it strikes the tiles, over what area, and over what period of time.  Higher forces concentrated in smaller areas over shorter periods of time are more likely to exceed the forces necessary to break the tiles, regardless of what provides that force.  -- Jayron 32 17:45, 20 November 2017 (UTC)
 * There is probably a bunch of measurements and stuff for ice at http://www.tms.org/pubs/journals/JOM/9902/Schulson-9902.html and refs (in particular #39), but I am a bit short on time right now to look at them. Tigraan Click here to contact me 18:10, 20 November 2017 (UTC)


 * You can break a floor tile with a rubber mallet, if it's not perfectly bedded.
 * Tiles are brittle. They are hard and strong, but they will not bend. If you support the tile on two sides with a wide gap in the mortar beneath, then any load on the top can cause them to bend, thus break. A soft impact (ice or mallet) might not give a sharp point, but if the ice is concentrated over an area smaller than the mortar gap, then even if the ice is crushed, the tile can still break. Andy Dingley (talk) 18:20, 20 November 2017 (UTC)


 * You may also be interested in Pykrete, a mixture of ice and sawdust which is bullet-proof and was seriously considered for the construction of a giant aircraft carrier called Project Habakkuk. Alansplodge (talk) 18:31, 20 November 2017 (UTC)

Mammoth Size
Why were woolly mammoths estimated to be smaller than other mammoths and elephants if they lived in cold climates? wouldn't they survive more easily in the cold if they were larger? אדנין (talk) 19:40, 20 November 2017 (UTC)
 * The premise is questionable. Woolly mammoth states that they were about the same size as the African elephant, the largest elephant species alive today. When it comes to other mammoths, Mammoth says that "most species of mammoth were only about as large as a modern Asian elephant", so that means that wooly mammoths were larger than most mammoths. - Lindert (talk) 19:49, 20 November 2017 (UTC)
 * According to this the Wooly Mammoth was about the middle in terms of size of Elephantidae. This notes "Mammoths and modern elephants overlap significantly in body mass."   This also has a size chart that puts the Woolly Mammoth right at the middle in terms of average size.  -- Jayron 32 20:08, 20 November 2017 (UTC)
 * But still, the Columbian mammoth and straight-tusked elephant lived in warmer climates, right? and they were still bigger than the woolly mammoth. אדנין (talk) 06:57, 21 November 2017 (UTC)
 * Quality and quantity of available food might have been a significant factor. Note that the last surviving woolly mammoths, on Wrangel Island, had become dwarfed: Island dwarfing is a phenomenon attributed partly to lower availability of food resources in a geographically restricted habitat. Assuming that woolly mammoths were woolly because they generally lived in colder climates than other mammoths, their available food resources are likely to have been poorer, too. {The poster formerly known as 87.81.230.195} 94.0.37.45 (talk) 08:43, 21 November 2017 (UTC)
 * Big size has advantages and disadvantages. Big animals are less threatened by predators but they usually also reproduce much slower. One theory in the science debate about Quaternary extinction event is that many species became distinct because of human hunting. If that was the truth, size did not matter much in sense of big elephant or small elephant because they where the delicious meat burgers which could not hide anyway. --Kharon (talk) 10:01, 21 November 2017 (UTC)
 * Despite their mammoth hide. ←Baseball Bugs What's up, Doc? carrots→ 13:20, 21 November 2017 (UTC)
 * The presumption that larger animals live in colder climates seems an odd belief to have, given the billions of counterexamples where it isn't true. -- Jayron 32 16:33, 21 November 2017 (UTC)
 * The presumption seems to be a misunderstanding of Bergmann's rule. B8-tome (talk) 18:49, 21 November 2017 (UTC)