Wikipedia:Reference desk/Archives/Science/2013 September 18

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September 18

Weight loss

How much exercise is needed to achieve 1 kg weight loss?86.171.126.239 (talk) 01:13, 18 September 2013 (UTC)

1 kg of fat contains 8000 Kcal of energy, a bit less than what your body burns in four days. If you exercise on a hometrainer at, say, 200 Watt then your body will actually burn 4 times as much because not all of the energy burned is converted in useful work. So, you will burn energy at a rate of 800 Watt. Half an hour exercise will then lead to approximately 800 Watt*1800 seconds/(4.18 Joule/Kcal) = 350 Kcal being burnt. If your metabolic rate does not get adjusted to compensate for this extra energy use and if you don't eat more, then it would take 23 days of exercise. If you are not very fit to begin with, you won't be able to exercise almost every day at this level, so it would take you a few months. Count Iblis (talk) 01:25, 18 September 2013 (UTC)

Note that for people who are physically fit, this calculation is invalid, because they have a body weight that is regulated tightly via feedback mechanisms. E.g. my body weight hasn't changed much over the years despite quite large changes in energy intake and use. I can eat 500 Kcal per day more without that having any effect on my body weight, I certainly won't gain 1 kg every 2 weeks as the calculation above would suggest. Count Iblis (talk) 01:47, 18 September 2013 (UTC)

Agreed. If you start with the assumption that "if everything else stays the same and I do X, how much weight will I lose ?", then you inevitably conclude that switching to sugarless gum will cause you to eventually starve to death. StuRat (talk) 03:05, 18 September 2013 (UTC)

No, that's a classical mathematical fallacy. Your metabolic rate is (all other things being equal ;-) proportional to your weight. So if you reduce your energy intake by a smallish degree, you will indeed loose weight "forever", but the infinite sum of weight losses converges to a finite total loss. It will not usually lead to starvation, but will asymptotically approach the new stable weight, where your new smaller body can persist on the new reduced energy intake. --Stephan Schulz (talk) 12:12, 18 September 2013 (UTC)

Yes, exactly. If you gain a pound in weight - you have to haul that extra pound around with you all the time - so you'll burn more calories as a result. If you switch to sugarless gum, saving (let's say) 100 calories per day - then your weight will gradually decrease (initially, at roughly 1 lb every 37 days) until your weight has dropped by enough that your normal daily activities are consuming 100 calories less than they did before. At that point, everything is in balance and your weight won't change until something else changes. Of course when you are halfway to that point - your rate of weight loss will be half of that...so your weight change will only asymptotically approach that new weight. It might take years of ikky-tasting gum to reach that ideal spot.

Similarly, when Count Iblis increasing his calorie intake by 500 calories per day he will put on weight - but only until his body stabilises at the new weight where he's sufficiently heavy that he's burning 500 more calories per day than before. Count Iblis seems very certain that his weight doesn't change - but it's unlikely that he can truly confirm because everyone's weight bounces up and down by as much as 4 or 5 pounds from one day to the next - it's the long term average that increases - and the slow rate of change is too small to measure without weighing yourself every day (preferably first thing in the morning) and calculating the longer term trend using graphs and math and stuff.

This is one reason why dieting is so depressing. You struggle to eat less - you get lots of initial success - but then your loss rate flattens out - and you have to eat even less to stay on that downward trend. After months of cutting out some favorite food, the knowledge that you have to cut something else out in order to keep losing weight is really upsetting.

Anyway - for our OP, just Google "exercise calorie calculator" - and you'll find dozens of web sites that allow you to input your body weight and get a long list of exercise activities and calorie consumption rates. Personally, I find those charts deeply depressing. Having to do an hour or more of fairly vigorous work to save the calories I get from one bag of potato chips is not my idea of fun! But YMMV. SteveBaker (talk) 14:20, 18 September 2013 (UTC)

Your metabolic rate remaining constant would be part of the faulty assumption that all other things will remain constant. Also, if you get 100 fewer calories from gum each day, your will be hungrier and eat/drink more calories, and/or have less energy and be less active, so burn fewer calories that way. StuRat (talk) 14:32, 18 September 2013 (UTC)

I think (but I'm not 100% sure, I asked a question about this myself above), that there are no actual experiments that points to the metabolic rate being kept the same except for the trivial effect of having to carry more or less fat with you. The overeating experiments that have been done on healthy fit people with a normal weight point to an active feedback mechanism regulating the metabolic rate instead of a passive one due to simply carrying your weight. The passive model predict weight changes that are an order of magnitude larger than are actually observed. Only in obese people does the model work, presumably because in those cases the feedback mechanisms regulating the weight have broken down, therefore assuming there is none will lead to a corect prediction.

It seems to me (but then I'm not a biologist) that an important point to being warm blooded is that you can fine tune your metabolic rate to suit your needs. What is known is that there are hormones that fat cells send to the brain when they are full or empty which influence the appetite. Since being able to keep your weight constant as much as possible is important for an animal living in the wild, you would expect that 200 million years of mammalian evolution would have led to a mechanism that prevents an animal that has to expend a bit more energy to get a bit less food from starving to death. We know that the brain does receive signals from the fat cells, so it's not that much of a stretch to think that these signals will also modulate the metabolic rate in such a way that the fat cells are kept filled at the same level. Count Iblis (talk) 16:47, 18 September 2013 (UTC)

Talking about mammalian evolution, for very many mammals its very much not about "keeping their weight constant", it's about efficiently laying in stores when times are good, so as to have reserves when times are bad. Part of our current obesity problem is that times are very rarely bad for most people living in developed societies. Grizzly bears, for example, put on about 50% of base weight in half a year or so. --Stephan Schulz (talk) 17:34, 18 September 2013 (UTC)

Also, note that as I estimated above, delivering 200 Watt power to a home traner for half an hour per day only leads to 350 Kcal beign burned. Now 200 Watt amounts to running at a decent pace for someone like me (weighing 58 kg). So, for me to burn 500 Kcal more per day would require me to put on an enormous amount of weight. This is totally inconsistent with my weight being stable at slightly below 60 kg for the last several years. About 6 years ago I was heavier (about 63 kg), I was eating less (about 3000 Kcal) and exercising less (3 times per week 20 minutes running, instead of about 50 minutes, five times per week). According to the calculation, I should now be a lot heavier than I was then (in fact so much heavier that I would be now be morbidly obese), yet I weigh less.

What I think is going on is that all these hormones that are involved in the feedback mechanisms implement an algorithm that calculates my ideal weight and tries to implement that as best as possible. If the outcome of that calculation is that I should weigh 58 kg, then that is exactly what will happen, no matter if I eat 3500 Kcal per day or 4500 kcal per day, unless I go outside the bounds of what this feedback mechanism can regulate. Count Iblis (talk) 17:13, 18 September 2013 (UTC)

Costa Concordia - What is/was its weight? I just don't get it.

Firstly, I am NOT an engineer. But I have followed with great interest both the sinking and salvage programme of the Costa Concordia. But I really don't get the vastly differing reports about its weight. How can it be 49,000 tonnes one minute and 114,000 tonnes the next, with various other weights being reported. Please understand that I am an engineering and mathematics simpleton who can only envisage putting the ship onto a vast and accurate set of kitchen scales and accepting the resultant figure as being absolutely correct. Thanks. 80.6.13.178 (talk) 14:10, 18 September 2013 (UTC)

The problem with ships is that there are at least five different measures of "weight" - there is "displacement" (how much water the ship moves out of the way when you lower it into the water) and actual "kitchen scales" weight. There is net tonnage, gross tonnage, or deadweight tonnage depending on the laden and unladen (with cargo) and fuelled and unfuelled state of the ship. Often, because it's kinda hard to actually weigh a ship - they measure it's volume and apply a tonnage figure to that. Frankly, the whole thing is a bit of a mess - and news reporters are very sloppy about which of those many numbers they use. In this case, the salvage folk are filling various tanks with water to alter the balance of the thing - so thousands of tons of water are also sloshing around in there. Displacement (ship), net tonnage, gross tonnage and deadweight tonnage may serve to confuse you yet further! SteveBaker (talk) 14:26, 18 September 2013 (UTC)

And don't forget that a good portion of it was underwater, so presumably filled with water, greatly adding to the weight, especially as that water was raised above sea-level. I imagine they raised the ship quite slowly, to let the water drain out as they go. StuRat (talk) 14:38, 18 September 2013 (UTC)

The displacement weight should be the 'kitchen scales weight', provided the ship isn't actually sinking or underwater. The others are measures of volume and safe loading capacity rather than genuine weight. Wnt (talk) 15:33, 18 September 2013 (UTC)

That's my understanding also. The Archimedes principle, right? It's complicated in this case, as noted above, by the devices they've used to right the ship and try to stabilize it - including the fact that it's resting on a platform. In fact, it looks like it's sitting lower in the water than it would be under pristine conditions. So it would be hard to measure its normal water displacement at this point. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:40, 18 September 2013 (UTC)

Well, they've got to get the water out of it before they can measure 'displacement' :) Wnt (talk) 16:09, 18 September 2013 (UTC)

For sure. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:26, 18 September 2013 (UTC)

But was is the purpose for measuring the displacement under normal conditions? The OP's comment is somewhat unclear. If you just want to know for personal reasons then that's up to you, but for those involved in the salvage knowing the effect of all that water would seem to be vitally important, in fact it would surely be more complicated then that knowing the weight of various sections etc. In other words, for a complex salvage operation it's surely not simple and while clarity on what is being referring to would help (obviously those actually involved don't suffer the confusion arising from media reports), there is likely a reason why various figures are bouncing around because all of them have various relevance. Nil Einne (talk) 12:18, 19 September 2013 (UTC)

I get the impression that one of the problems is the design of this type of cruise ship, which has a large amount of superstructure above the height of the hull. See Are Cruise Ships Dangerously Top Heavy? and the linked Why Mega Cruise Ships Are Unsafe: Opinion. Expert opinion seems to contradict this Modern cruise ships are safe, says Robert Ashdown after Costa Concordia incident but when all those upper accommodation decks are full of water, it has got to make it harder to tip it back again. Alansplodge (talk) 18:34, 18 September 2013 (UTC)

• The basis for the wrong "top heavy" opinion is the assumption that the ship mass is roughly directly proportional to volume. If that were true, then the center of mass would be above water, and the ship would be in unstable equilibrium, and indeed unsafe - but that would also mean the slightest rock to the side could mean the entire ship falls over, which clearly doesn't happen since it's known that cruise ships are supposed to be able to travel through hurricane conditions (Carnival does not cancel cruises through hurricanes). Any stable boat should have its center of mass below water so it is at stable equilibrium - cruise lines won't buy ships that are "top heavy". The magnitude of the forces exerted by the stabilizers is not nearly enough to completely replace static equilibrium (as evidenced by the fact that the Carnival Triumph did not capsize after losing power and being blown by winds), especially if you think that the ship's mass is on the order of tens of millions of kilograms, meaning that even the main engines could not right the ship very quickly (F=m*a) - it's clear the second link's article is wrong in this respect. However, water coming in changes everything, since it brings the overall density of the flooded part closer to the density of water (because the ship is mostly hollow).--Jasper Deng (talk) 04:08, 20 September 2013 (UTC)

FWIW Wikipedia gives its gross tonnage as 114,137 tonnes.--Shantavira|^{feed me} 18:36, 18 September 2013 (UTC)

• I don't see why it should be so hard to "weigh a ship" by measuring displacement. The shape of the hull would almost certainly be in a computer model somewhere, then you just see where the waterline is and calculate the volume and hence weight of water displaced. However, this may be putting the cart before the horse, or the chicken before the egg, or whetever the expression is, since surely the designers have to know the finished weight of the ship reasonably accurately in order to determine in advance where the waterline will be, don't they? All that would surely have to be worked out before the ship was even built. 86.160.220.5 (talk) 19:25, 18 September 2013 (UTC)

  Yes, but what is "the ship". The superstructure alone? The superstructure and the engines? The carpeting and furniture too? With or without passengers? With provisions and linens? Etc. All of that changes what you are measuring. Certainly, it has all been figured out, to exhausting detail, but you need to define what you are weighing before you can actually weigh it. --Jayron32 20:05, 18 September 2013 (UTC)

Obviously. My point is that the real weight of a ship (in some defined state) must be known or fairly easily calculable, hence the reason for the other measures being used cannot solely be to do with the difficulty of getting a real weight, at least not in modern times. 86.160.220.5 (talk) 20:39, 18 September 2013 (UTC)

The problem (in part) is that these peculiar standards for how ship weights are specified weren't "in modern times" - things like net/gross/deadweight-tonnage were specified in the 1600 or earlier. In something like a cargo ship, the weight of fuel and cargo out-weigh the ship itself by a considerable factor...so the difference between these various measures is highly significant. SteveBaker (talk) 21:06, 18 September 2013 (UTC)

Right - I think I get it now. If I weigh myself naked in the morning - as I do every morning - before I have a pee, I will weigh more than I would do after having a pee. But once I have then had a mug - not a cup - of tea, I will weigh more than I did after having a pee, but less - perhaps - than I did before having a pee - depending upon how much urine my kidneys have discharged into my bladder during the night. But if I then weigh myself after having a hot steamy shower - and after having said pee, but before drying myself off, who knows how much water has seeped into my open pores? And subsequently, how much might I weigh? And of course, if I do dry myself off and thus remove all the surface water, but still retain the epidermal absorption of water, plus the tea, then again, the question arises, how much do I actually weigh? I must consult my Family Doctor (who also has a Ph.D in Philosophy)(and who always weighs me on his clinical scales whilst I am fully clothed) for his informed opinion. But thanks for all the foregoing opinions. I really do appreciate them. but I still don't know the weight of the Costa Concordia. 80.6.13.178 (talk) 22:22, 18 September 2013 (UTC)

I just added a figure of 50,000 for displacement based on a Spiegel article. The gross tonnage has led me to start Wikipedia:Reference_desk/Mathematics#Inverse_of_gross_tonnage. But crudely, taking 114147/0.20 -> 10 ^ 5.75643451; 114147/0.3151286902 = 362223 = 10 ^ 5.55897602 etc. I get that the gross tonnage of 114147 / 0.3112860998 = 366695 cubic meters. Note that 50,000,000,000 g / 366,695,000,000 cm^3 = 0.1363 g/cm^3, or less than one-seventh the overall density of water - i.e. more than 6/7 of the ship's volume was out of the water. Unless I fouled up :) Wnt (talk) 23:25, 18 September 2013 (UTC)

Not after Captain Schettino had finished with it, it wasn't. 80.6.13.178 (talk) 08:19, 19 September 2013 (UTC)

We owe him a debt of gratitude, having taken a rather unstable ship and moved it into a much more stable position. :-) StuRat (talk) 13:18, 19 September 2013 (UTC)

That's in very poor taste, so as long as we're at it... we should be thankful that this captain had such uncommon skill as to manage to capsize his ship so close to land. Indeed, if he had managed to make it just a hundred or so meters further inland, I imagine his passengers should have walked off the boat without any danger at all, and its 'displacement' would have been zero. Wnt (talk) 20:39, 19 September 2013 (UTC)

StuRat is joking. At least I hope he is. It's kind of like an airplane pilot, completely though his own incompetence and ignoring of basic safety provisions, manages to loose control of the airplane and crash it - but by some fluke of circumstances on the way down in panic twists the controls and thus by complete accident comes down in a dense field of corn which cushions the impact. So Stu would feel we should be gratefull to the pilot, who never planned any of it - but claimed he did after the event of course. 121.215.11.211 (talk) 03:53, 20 September 2013 (UTC)

• Gross tonnage is not a measurement of mass, nor weight. It's only a dimensionless figure that has little relation to the actual mass of the ship; it is a function of only the ship's volume (given by $G(V)=V(.2+.02\log V)$, V in cubic meters, - the only way I know of to recover volume from gross tonnage is Newton's method, since you can't exactly solve for V in terms of G). The reason we can measure weight by displacement is archimedes' principle, which relates weight, and thus (with known gravity) mass, to volume of water displaced, by virtue of its density. As previously mentioned, there are many different factors, but gross tonnage is kinda misnamed, in my opinion, since it is not a measure of weight or mass.--Jasper Deng (talk) 04:01, 20 September 2013 (UTC)

If I could make a bet on short odds that StuRat (who is entirely unknown to me) had Italian Blood in his veins, I would put my House, Car, Daughters and Retirement Fund on him. 80.6.13.178 (talk) 12:20, 20 September 2013 (UTC)

Nope, you lose, when can I pick up my winnings ? In case you are curious, I am of French and English blood, but also with a fifth of Scotch in me at any given time. :-) StuRat (talk) 01:54, 21 September 2013 (UTC) o

Bonjour mon Ami. I forgot to include my 89 year old Mother-in Law who left home in 1939 to join the British Women's Army in the struggle against Germany in the 2nd World War. When Adolf Hitler found out he committed suicide. When can you collect her? 80.6.13.178 (talk) 09:54, 21 September 2013 (UTC)

Experiments in the Revival of Organisms

This page has quite a bit of discussion as to whether or not this soviet medical reel featuring J.B.S. Haldane really shows a decapitated dogs head being kept alive and responding to stimuli through use of a blood transfusion machine. What kind of peer review would be needed to prove this procedure is factual, would multiple dogs need to be decapitated within the last five years to provide a Wikipedia MEDRS? What is the minimum number of experiments needed for a review article to be published on this subject? The page seems not to be under wikiproject medicine; but shouldn't it be if it can be proven the procedure is real? Thank you for answering these emotionally difficult questions. CensoredScribe (talk) 16:44, 18 September 2013 (UTC)

Wikipedia policies are no part of science, so I think discussion and answers should be referred to the duplicate thread at Talk:Experiments_in_the_Revival_of_Organisms#Peer_Review_and_Wikipedia_MEDRS. Wnt (talk) 17:15, 18 September 2013 (UTC)

(after e/c)

If the soviet experiment is under dispute, it would be difficult, if not impossible to prove that that particular experiment was real. However, if new evidence about that experiment came to light, and reputable sources said the experiment was confirmed authentic, then zero new experiments would need to be performed.

Or, The procedure itself could be verified under better controlled conditions. There's no particular minimum number of experiments that would have to be run. If the head is going to survive more than a few seconds, you wouldn't even need a control group. Unless there's some weirdness that makes this procedure dog-specific, you wouldn't even need to use dogs.

However, none of these decisions are really what makes an article a reputable source on Wikipedia. For that it would need to be a peer-reviewed paper that is mostly accepted by the scientific community as reputable. APL (talk) 17:19, 18 September 2013 (UTC)

Right. We basically need the same thing we would need for any article -- reputable published sources. Looie496 (talk) 18:22, 18 September 2013 (UTC)

It's nothing to do with the number of dogs involved. It's simply the number of third party papers that were written to support that work. WP:RS is the bible here - and it says nothing about the number of experiments or the scale of them. What matters is what other scientists in the field of biology (or whatever) had to say on the matter. SteveBaker (talk) 21:02, 18 September 2013 (UTC)

Vertical-slit marsupium

planes of the body

My biology question relates to marsupials:
Is there a term used for distinguishing a marsupium (pouch) which is a vertical slit (e.g. Sugar glider) from the more familiar horizontal 'pocket' (e.g. Kangaroo)? -- Thanks, ~E 71.20.250.51 (talk) 17:54, 18 September 2013 (UTC)

You might look in Walker's Marsupials of the World. My copy is in storage. μηδείς (talk) 21:39, 18 September 2013 (UTC)

No luck. Any biology wonks out there? ~E:71.20.250.51 (talk) 21:03, 20 September 2013 (UTC)

The terms transverse and sagittal, or longitudinal, are available. I am surprised we do no have an article on body planes. μηδείς (talk) 01:58, 22 September 2013 (UTC)

Falling into a black hole

If at event horizon an infalling observer uses all its energy to escape a black hole, how much would be the longest time to reach the singularity of a, for example, six million solar masses' black hole? And if an object has on event horizon a speed=0 how much would be the time? Thanks for answering, 95.234.227.16 (talk) 22:25, 18 September 2013 (UTC) PS: I'm particularly referring to Gullstrand-Painleve coordinates — Preceding unsigned comment added by 95.234.227.16 (talk) 22:27, 18 September 2013 (UTC)

speed zero? with respect to what? Dauto (talk) 23:56, 18 September 2013 (UTC)

The PS to the OP's question is crucial here. He's talking about a speed of zero as measured in Gullstrand–Painlevé "rain" coordinates. Red Act (talk) 13:26, 19 September 2013 (UTC)

Whoops, sorry, from the OP's addendum below, it looks like he wasn't actually intending to ask about a speed of zero at the event horizon as measured in GP coordinates. Red Act (talk) 16:17, 19 September 2013 (UTC)

In geometrized units, the answer to your first question is $\pi M$, and the answer to your second question is ${\frac {4}{3}}M$. See equations 1 and 19 of this paper, and the end of the article section Gullstrand–Painlevé coordinates#Speeds of raindrop. I'll leave it up to you to plug in whatever specific value for M you want, and to do the conversion between SI and geometrized units. Red Act (talk) 13:26, 19 September 2013 (UTC)

Yes, but the formula "4/3 M" is for an object free falling from infinite, I meant an object that on event horizon has a zero-speed respect to black hole and an infalling observer that uses all its rocket energy to get outside. 95.235.9.203 (talk) 14:52, 19 September 2013 (UTC) PS: I searched especially the formula, but the value I gave for mass is six millions solar masses. — Preceding unsigned comment added by 95.235.9.203 (talk) 14:54, 19 September 2013 (UTC) X Another curiosity: but for an infaling observer the view of external universe does disappear (I mean concentrates in a point with infinite luminosity) at event horizon or at the singularity? This because I read contrasting papers. 95.235.9.203 (talk) 15:32, 19 September 2013 (UTC)

Neither one is possible. It is not possible to "hover at the horizon (zero speed), and it is definitely not possible to get outside of the Horizon (no matter how much of your own energy is used) Dauto (talk) 22:20, 19 September 2013 (UTC)

Your PS about Gullstrand–Painlevé coordinates threw me off. You are apparently actually interested in the case of starting with a speed of zero at the event horizon as measured in Schwarzschild coordinates, not a speed of zero as measured in GP coordinates. As Dauto points out, it isn't possible to hover right at the event horizon with a speed of zero as measured in Schwarzschild coordinates, because that would require an infinite amount of energy. However, if you're considering observers who are in free fall starting from the initial conditions of having a speed of zero as measured in Schwarzchild coordinates at an initial Schwarzchild r coordinate of r₀, with r₀ greater than the Schwarzchild radius, then in the limit as r₀ approaches the Schwarzchild radius, the proper time that will elapse before the observer will hit the gravitational singularity is πM in geometrized units. That limit is also the maximum possible proper time that can elapse for any infalling observer between crossing the event horizon and hitting the gravitational singularity, even if the infalling spacecraft fires its rockets. For support for my statements above, see the paper I linked to in my earlier post.

One solar mass in geometrized units is about 1.5 km, so if M is six million solar masses, then πM is 2.8 x 10¹⁰ m, which in SI is about 94 seconds. Red Act (talk) 00:51, 20 September 2013 (UTC)

I think the papers you've seen that differ about the point at which the view of the universe's stars will coalesce into a point differ because they're considering different things. For an observer that's freefalling into a black hole, the view of the stars won't coalesce into a point until the observer hits the singularity. But for an observer outside the horizon whose speed is zero as measured in Schwarzchild coordinates, the view of the stars will approach a point as the observer's location approaches the horizon. Even at the same event, the frames of reference of the two observers are very different, due to their huge speed relative to each other. Red Act (talk) 13:28, 21 September 2013 (UTC)

I understood. Just another two curiosity: a photon that on event horizon radially moves outward black hole would remain stuck at event horizon or would fall to singularity (and if yes, in how much time?)? And if I (hypothetically, obviously) could surpass into a black hole the light's speed I could escape or I equally would finish to singularity because there aren't way to escape? Thanks for answering, 95.235.218.183 (talk) 11:36, 20 September 2013 (UTC)