Wikipedia:Reference desk/Archives/Science/2014 October 16

= October 16 =

Greased sword
There is a sword fight, one person gets slashed in the chest and has a huge gaping wound. What would happen if the sword and the person's chest were oiled and slippery, would the sword cut less? — Preceding unsigned comment added by 88.115.38.169 (talk) 17:16, 16 October 2014 (UTC)
 * Only maybe if the blow was struck by the side of the sword rather than the edge. For a gross comparison, the oily surface of a cooked bird doesn't seem to stop the carver from getting through it. ←Baseball Bugs What's up, Doc? carrots→ 17:32, 16 October 2014 (UTC)
 * I agree, it seems unlikely that it would make any difference whatever unless it was an extremely glancing blow.  Do an experiment - get an egg and a knife...whack the egg hard with the sharp edge of the knife...what happens?   Cover both with olive oil...do it again.   Does it make a difference?  No?  I didn't think so.  SteveBaker (talk) 20:08, 16 October 2014 (UTC)


 * A greased sword should go through a bit quicker, but not a significant bit. Remember, blood is already slippery. Once the sword's in, it's lubed. In boxing and MMA, they put Vaseline on fighter's faces to prevent friction and tearing, and the same idea would help somewhat against clubs and such, but swords (and elbows) work too finely. InedibleHulk (talk) 13:13, 17 October 2014 (UTC)

How many molecules build the cell? (not types, but in general)
What is the amount of the molecules that the cell made of? 5.28.154.216 (talk) 19:03, 16 October 2014 (UTC)
 * What type of cell? Crystal cell unit? Bacterial cell? Eukaryote cell? What species if one of the latter two? What tissue? --OuroborosCobra (talk) 19:07, 16 October 2014 (UTC)
 * It is unlikely that an exact answer can be determined for any specific case; but we can estimate to order of magnitude. We have a few entries in our article on orders of magnitude (numbers), with citations: the human body consists of roughly 1014 cells, and 1027 atoms.  With a little arithmetic, you can estimate an average number of atoms per cell.  This leaves the original question unanswered: how many atoms are in each molecule?  Well, the answer is very difficult, because there are some molecules (like water) comprised of very small numbers of atoms... water has three atoms.  There are other molecules, like DNA, which is commonly treated as a "single molecule," containing millions of nucleotides (potentially hundreds of millions of atoms per molecule).  The arithmetic mean value of atoms-per-molecule is not very useful!
 * So, we probably have a few trillion atoms in a typical human cell (plus or minus a few trillions, or maybe even plus or minus ten trillions or a hundred trillions); and the number of distinct molecules made from that many atoms could be anywhere from a few million to a few hundred trillions. This is somewhat imprecise, but it's not easy to improve the precision without relying on a lot of difficult and tenuous estimations!
 * Nimur (talk) 19:38, 16 October 2014 (UTC)


 * Quick answer: twenty billion.


 * OK - that's going to make people wonder - so I'd better explain how I got there:


 * It's very hard to generalize - but I think you're probably asking for an extremely approximate answer (which is all you'll ever get!). The smallest known cells (some bacteria) are only 200 nanometers across (there are yet smaller things at 20nm - but there is much debate over whether they are alive...or even exist at all!).   The largest cells known are the nerve cells of a giant squid that can be 80 feet long...and the heaviest is an unfertilised ostrich egg.   But assuming we're talking about your typical run-of-the-mill human cell, what can we say?


 * According to this paper, a "typical" human cell weighs 10-12 grams.


 * This image has the percentage of different molecules in a bacterial cell - it's probably not THAT much different from a human cell - so let's guess that human cells have about the same distribution...that might be a bad guess - but we're only after a very rough answer.
 * DNA is only 1% of the cell by weight - and DNA molecules are huge - so it's not contributing many molecules...so let's ignore it
 * Same thing could be said for the proteins, RNA and other long-chain molecules. They don't make up much of the mass - and they are relatively big molecules.
 * Water is 70% of the mass of the cell - and it's made of very light molecules...so it's going to totally dominate the molecule count.


 * So it's probably fair to say that the total number of molecules is pretty close to the number of water molecules - at 70% of the mass of the cell. The other 30% doesn't contain many molecules - because, those are mostly REALLY gigantic molecules!


 * The molecular weight of water is 18 - so 18 grams of water is 6x1023 molecules (Avagadro's number).
 * 70% x (10-12) x (6x1023) / 18 = 23,000,000,000


 * So: the total number of molecules in a human cell is probably a little more than the number of water molecules, which is around 23,000,000,000 - which we'd better round to 20 billion.


 * Or a few million...or trillions of quadrillions...depending on what cell you're measuring.
 * SteveBaker (talk) 20:00, 16 October 2014 (UTC)