User talk:DirkvdM/Dutch National Science Quiz 2011

I have given my answers and reasonings without looking anything up. DirkvdM (talk) 08:37, 19 December 2011 (UTC)

1.
After pouring the drink, champagnebubbles rise faster than beerbubbles of equal size. Why? a. Because of the higher viscosity of the beer. b. Because proteins stick to the beerbubbles as they rise, giving them a higher resistance. c. Because of the higher gas-pressure in champagnebubbles, which increases the upward force. Before reading the answers, I thought that it would be the viscosity, and that is indeed one of the answers. However, answer b sounds plausible too; beer does indeed contain proteins and I believe they do have a tendency to stick to surfaces (or each other). Answer c seems nonsense. The pressure inside the bubble is equal to the pressure excerted by the drink (at a given depth). For champagne this would actually be slightly lower since it contains more alcohol and is therefore lighter (assuming it's 'ordinary' champagne and beer). But if indeed at first the pressure is higher, then the bubble would grow and a bigger bubble has less surface per content, so that would cause less resistance and a faster rise. But the greater upward force is then because of the size of the bubble, not the gas-pressure. And anyway, this makes the 'equal size' in the question ambiguous. DirkvdM (talk) 08:37, 19 December 2011 (UTC)


 * You may want to check pearling dynamics (which, unfortunately is a redlink). Speed of rise of a bubble is dependent on two things: size of the bubble when it detaches from the glass surface and viscosity of the medium that it travels through (think extremes: soda water vs. maple syrup). Acceleration of a bubble is dependent on two things: air pressure change and nucleation. Air pressure change is negligible in a glass - you need to have a glass that is about 20 feet tall to get any noticeable change. Nucleation causes more gas to enter the bubble, making it bigger, making it move faster. The more viscous the medium, the less nucleation you will have. So, viscosity appears in both speed and acceleration. -- k a i n a w &trade; 17:22, 19 December 2011 (UTC)

Official answer The correct answer is B. Dissolved proteins, which are found in both champagne and beer, collect on the edge of the bubbles. In Champagne the bubbles grow so quickly that the protein has difficulty forming a proper layer. Because beer bubbles grow much slower, the proteins collect more easily on them. They form a kind of layer around the bell. It's no longer really a bubble, but rather a sort of protein ball. As a result, the beer-bubble has to plow its way through the beer and rises more slowly.

2.
Most olympic swimming pools are 3 m deep. What happens to the swimming times of the contestants of an olympic sprint if the water were only 1,5 m deep? (Note that I maintain the 'decimal comma' in the translation, as suggested by the SI system.) a. the swmimming times all rise equally. b. the swmimming times go further apart. c. the swmimming times get closer together. Way too many variables, I'd say, but here goes. I assume that they mean the absolute differences in the times, not the ratios. So if the times of two swimmers go from 20 s and 19 s to 21 and 20 s, the answer would be a. The speeds of the swimmers will decrease because the water has less room to flow underneath the swimmers, giving more resistance (although part of the water will flow along their sides). As a result, the speeds go down. So one would think that that is percentage-wise the same for all contestants, in which case the times would get closer together. However, resistance increases with speed, and even exponentially so (F = &frac12;ρv&sup2;Ac, if I remember correctly (c being an experimentally determined constant)), so this would mean that with the lower speeds the faster swimmers have a relative advantage (or less of a disadvantage), which suggests answer b. As said, the water also has 'outlets' at the sides, wich will become more prevalent as this resistance rises, reducing the first effect. But then the neighbouring swimmers will cause a similar effect, putting a limit to how far that can go. That is, assuming they swim side by side. The swimmer that has the fastest start wil be less troubeld by this. What's more, as a swimmer in a neighbouring lane tries to catch up, his 'displacement wave' will propell the faster swimmer and give the straggler extra resistance. There will always be this effect, but it gets greater with reduced depth. But this all sounds a bit too 'contrived' to feel comfortable, so I assume I'm missing something. Or maybe the questioneers didn't think of all this, or ignored the possibility that some might take all this into account (I can never fill out a questionnaire because I end up writing down more questions than answers :) ). My (overeducated?) guess is b. DirkvdM (talk) 08:37, 19 December 2011 (UTC)


 * This came up during the Beijing Olympics. The pool was changed from 2m to 3m. Swimming times were faster. New Scientist magazine did a study and the conclusion was that the deeper water dissipated more turbulence, creating less resistance. Others at the time noted that in the dive, the swimmers near the bottom of the pool. When under the water, they swim faster. So, having a deeper pool means that they have more underwater time, meaning they have faster overall swim times. I believe it is a combination of those two things - if not more variables. But, the conclusion is clear - a 3m deep pool produces faster swim times than a 1.5m pool. Unfortunately, this question appears to asking about the deviation in swim times - which was not an issue covered in any of the studies that I saw. -- k a i n a w &trade; 17:30, 19 December 2011 (UTC)

Official answer The correct answer is C. When water flows past an object (in this case a swimmer), this results in a pattern of pressure variations in the water. If a swimmer swims in shallow water, this pattern is disrupted by the bottom and is rearranged. The swimmer feels this as an extra resistance. The faster a swimmer swims, the greater this pattern becomes. This means that the fastest swimmers encounter more resistance in shallow pools. Their swimming speed will decrease slightly more than that of the slower swimmers. The swimming times are therefore closer to each other. Recreational swimmers swim too slow to notice this extra resistance in shallow pools.

In the tv show, a calculation was done with the Froude number (F).
 * F = v / √gd

so
 * d = v² / gF²

If F > 0,6, the resistance suddenly rises (if calculated with SI units). So filling in that and the speed of the world record holder, this becomes:
 * d = 2,463 / 9,8 * 0,6 = 1,72 m

So at a depth lower than that, the fastest swimmers get a sudden increase in resistance.

3.
At Facebook you can see how many friends your friends have. Do people on Facebook on average have as many friends as their friends have? a. Yes. b. No, on average their friends have more friends than they do. c. No, on average their friends have fewer friends than they do. I've never been there, but I'll assume friendship on Facebook is two-way and that some people don't have any friends. (Alas only the second is like real life. :) ) Thje question is rather ambiguous (I double-checked, but the translation is correct). It suggests it's only about people who have friends. I that case I'd say the answer is a. Which is a little too simple, unless I miss something. If it is about all people, including the ones witout friends, then how many friends do the friends of people without friends have? They don't exist, so don't they count or do they have zero friends? In both cases the answer remains a. Or is the question two-part? The first part is about 'people on Facebook' in general, so that includes the ones without friends. The second part, however, limits it to those with friends, and those friends have at least one friend. That is one more than those without friends, so the answer would be b. But that is twisted logic. So I'll stick to a. Sometimes the obvious answer is the correct one. This is not QI. :) DirkvdM (talk) 08:37, 19 December 2011 (UTC)


 * Use statistics (woohoo). Given a random population of U users, randomly create F friendships. F should be more than U, but far less than U2/2 (the maximum number of friendships). Do a frequency count of those with 0 friends to those with U-1 friends. You will find that a minority has the most friends. That means that the majority has less friends than their friends. I ran it over and over and over and I get around 60% of people (variable to my values of U and F) have less friends than their friends. According to this, 84% of Facebook users have less friends than their friends. -- k a i n a w &trade; 18:18, 19 December 2011 (UTC)


 * The people with few friends get counted few times (among all users) when computing the average; those with many friends get counted many times. (Put differently, of course your friends have lots of friends &mdash; everyone is friends with them, including you!)  So it's B.  --Tardis (talk) 14:14, 20 December 2011 (UTC)

Official answer The correct answer is B. If everyone has the exact the same number of Facebook friends, then the average number of friends is equal for everyone. However, not everyone has the same number of friends. So for the majority your friends have on average more friends than you. This phenomenon is called the friendship paradox, formulated in 1991 by the American sociologist Scott L. Feld. Chances are that you're friends with someone who has many friends. Imagine that someone has ten thousand friends, then there will be at least ten thousand people who have a friend who is very popular. Such a popular person pulls the average up tremendously, for all his ten thousand friends on Facebook have a friend who has ten thousand friends. This applies to all social networks, not just Facebook. A simple example to illustrate this. See the diagram at the answers-page, where #V is the number of friends, #VvV is friends of friends and gem is average. There are 11 friends: Arend, Bert, Cor ... etc. If they are connected with a line in the diagram, they know each other. We can now see how many friends they have. A has two such friends, namely B and E. The column shows how many friends the friends of each person have. So the friends of A, namely B and E, have respectively 3 and 8 friends. The rest is also shown in the table. Now we can calculate how many friends the friends of each person has on average. For example, A has 2 friends who together have 11 friends, on average 5 ½ friends per person.

4.
You carefully drop a 1 mm large drop of water on a metal plate with a temperature well below the point of freezing. What shape will the ice-drop get? a. It gets a perfectly round top. b. It flows out flat and then freezes like a sort of pancake. c. It gets a pointy top. I think I've got this right. Of course the part that touches the plate first freezes first. Above that, there is a stagnation point (just like at the opening of a pitot tube or at the front of a sail). This is where the water can't go anywhere because it's surrounded by equal amounts of water on all sides. The water at the sides can flow down and further to the centre it's ever more stagnant. Stagnant water freezes faster than moving water, so the next water to freeze is the water above that first freezing point. Etcetera, until there is no more water above it. The surrounding water was lower in the first place and has had more opportunity to move even further down. So it gets a pointy top. Answer c. However, there's a possible snag. The point on the plate where most water freezes has heated up in the process. And a transition point requires a lot of energy, so that is not negligible. I suppose that's why the plate is well below the point of freezing (although that doesn't entirely dissmiss the point). DirkvdM (talk) 08:37, 19 December 2011 (UTC)


 * You pretty much got it right. This paper has photos of the little pointy drops. What you omitted was the possibility of water vapor being attracted to the drop, increasing the height of the pointy tip. -- k a i n a w &trade; 18:39, 19 December 2011 (UTC)


 * Thanks for the vids. Turns out I got the answer right, but what happens is quite the opposite of what I described. I thought the water would try to flow out on the plate, but freeze during that process. However, it forms a drop on the plate. It all stagnates, so to say, so there is no stagnation point. I underestimated the surface tension. DirkvdM (talk) 09:15, 20 December 2011 (UTC)

Official answer The correct answer is C. When you gently drip a tiny drop of water on a cold plate with a syringe, you see that it is a perfect sphere. The drop is so small that gravity has no grip on it. But it does not retain this roud shape. A curious property of water is that it expands when it freezes. You see the drop slowly freeze from the bottom up. The ice, which grows from the bottom up, 'corners' the still unfrozen water. The unfrozen water still retains a bit of a spherical shape because of surface tension, but because of the expansion of the water, the freezing ends with the droplet forming a sharp point.

In the tv show, this was demonstrated, using a metal plate dipped in liquid nitrogen. A video similar to the one linked to by kainaw was also shown. This phenomenon has been researched at the University of Twente since 1996 and is only recently understood. Silicon also has this property that it expands when it freezes, so this research is relevant for the computer industry, to figure out how the crystallisation of silicon works, so they can make purer crystals.

5.
A gps-satellite is just before launch always set such that the clock is just a fraction slower than clocks on Earth. Why? a. To compensate for the higher speed of the satellite. b. To compensate for the changed gravity working on the satellite. c. To compensate for the lower temperature of the satellite. I think I've got this right. C sounds like nonsense. If anything, a low temperature will slow things down, so the clock would then actually have to be set faster. A actually is the wrong way around. A higher speed does make time slow down. So the clock would then again have to be set faster. B must be right then. And indeed, I believe gravity also affects time. The lower gravity, the faster time goes, so the clock has to be slowed down. And this effect is bigger, because if the satellite has the same radial speed as Earth, the speed will increase proportionally to the distance, whereas gravity decreases exponentially with the distance. DirkvdM (talk) 08:37, 19 December 2011 (UTC)


 * Both general and special relativity play a part here. Special relativity deals with speed here. The satellites are moving fast. They will tick slower. Exactly how much slower? At their height, they have a constant speed which decreases tick time by less than 10,000 ns/day. But, general relativity says that clocks in a lower gravitational field will tick faster. At the satellites height, they will tick faster by about 50,000 ns/day. General relativity wins out. The satellites have faster ticks, so they have to be set to tick slower before liftoff. -- k a i n a w &trade; 18:46, 19 December 2011 (UTC)

Official answer The correct answer is B. Shortened answer: Time slows down with increased speed and with increased gravity. This can be calculated with Einstein's theory of relativity. The speed of the satellite will make the clock slow down by 7 millionth of a second per day. The reduced gravity will make the clock speed up by 46 millionth of a second. The net result is that it will speed up 39 millionth of a second, so it has to be set that much slower.

6.
You've got your shirt on inside out and your hands are tied with handcuffs. Is it possible to get the shirt on right without untying your hands? a. Yes, albeit with some difficulty. b. No, your shirt will end up upside down. c. No, your shirt will end up back to front. I'm pretty sure I've got this right. Simplify this to a topological model: a ring with a tubular piece of cloth around it that has openings at either end. Actually, make it a bar that is infinitely long. There also happen to be two more holes in the 'sock', with two blobs protruding from them (head and body), but these are irrelevant for the model. Now just pull one side of the sock over itself until it has completely turned inside out. Front and upside will remains front and upside. So answer a. In practise, of course, these blobs do get in the way, but note that there is no answer that says it's impossible in practise. That's why answer a says 'with some difficulty'. The shirt has to stretch a fair bit. Also, after this operation, the shirt is on one sleeve, so you have to pull it over your head and body again. DirkvdM (talk) 08:37, 19 December 2011 (UTC)


 * You are correct. This is a "party trick" in police circles. Handcuff a guy and tell him to try and turn his shirt inside out. Take off the shirt. You can get it off your head, but your arms will be in the sleeves. Pull the entire shirt through one of the sleeves. Put the shirt back on. -- k a i n a w &trade; 18:51, 19 December 2011 (UTC)

Official answer The correct answer is A. What you have to do is take off the shirt over your head. The shirt is now on your hands the right way round. Then pull it inside out again by pulling it through one of the sleeves. Now if you putit on again it will be the right way around again.


 * This was demonstrated for real, but also in a more topological way with a shirt on a ring, just as I suggested. DirkvdM (talk) 19:36, 27 December 2011 (UTC)

7.
It is like trees know where other trees are. Why is it that grown trees don't 'repress' (*) each other or touch each other with their branches? ((*) I couldn't think of a better translation.) a. They detect signal chemicals which neighbouring trees give off to the ground water through their roots. b. They detect the light spectrum that comes off their neighbouring trees. c. They detect the oxygen that their neighbouring trees produce through photosynthesis. Branches and roots mirror each other's shapes to some extent, but nowhere near enough, so it can't be a. The light spectrum sounds like the most precise form of 'measurement', so my guess is b. DirkvdM (talk) 08:37, 19 December 2011 (UTC)


 * I do not know, but this may be related... I read a study about flowers in a pot. If two flowers are grown from clippings or seeds from the same parent, they will grow close to one another in a pot without problem. If they come from different parents, they will purposely grow roots in the direction of the other flower, which results in one flower killing the other. Then, after reading about that, I looked for more and found a study about grapes. If two grape vines are clipped from the same parent vine, they can grow side-by-side. If they are clipped from different parents, they will grow roots towards one another, causing one of them to become weaker. So, it is very possible that trees behave in the same way. I always figured that trees need sun and if they grow too close to an existing tree, there's too much shade. -- k a i n a w &trade; 18:56, 19 December 2011 (UTC)


 * The question specifies that the trees don't 'repress' each other (let alone kill). Maybe that happens in an early stage, but once they're full-grown they compete in differrent ways. For example, it makes sense that if a tree gets overshadowed by a neighbour, it's growth-effort goes into height instead of width. There is no gain in letting its leafs 'interleave' with those of the neighbour. And if it can't outgrow its neighbour in height, it makes more sense to grow wider on the other side and maybe compete with trees there. If it loses that too, it will die. DirkvdM (talk) 09:30, 20 December 2011 (UTC)

Official answer The correct answer is B. White sunlight is composed of different colours of light. You can see when you look at a rainbow. When white light reaches a leaf, some colours of light are reflected and other absorbed. The colours that are absorbed lose some energy and as a result the coour changes a bit. This changed light continues through the leaf and thus the composition of the light under a tree different from above it. Other trees can detect this light with their leaves using special proteins, which are 'activated' or not by different colours and influence the growth. A different colour ratio in the light results in a smaller number of active growth proteins which decreases the growth in that direction.


 * Two days ago my brother took me for a walk through a former production forest that had been bought by a nature organisation to let it revert to a more natural state. In order to give nature a hand they cut down many trees. That made me think of my answer to this question. For a production forest it makes sense to plant the trees unnaturally close together. If they are all the same trees of the same age, tghey will start competing but not winning, all of them putting all their energy into growing tall. This will result in better wood with fewer side-branches and therefore fewer knots. DirkvdM (talk) 19:50, 27 December 2011 (UTC)

8.
There is a fairly recently discovered discharge-phenomenon above the clouds that is named after a creature from a play by: a. Sophokles b. Shakespeare c. Goethe I believe this phenomenon is called a sprite. Don't know from plays. (What is this question doing in a science quiz anyway?) DirkvdM (talk) 08:37, 19 December 2011 (UTC)


 * It is "b". We have an article on it. -- k a i n a w &trade; 18:57, 19 December 2011 (UTC)

Official answer The correct answer is B. Shortened answer: They're called sprites. In science, usually descriptive names are used, but because the cause of the phenomenon was not known, a 'random' name was picked, so it would not give a false impression about the cause.

9.
On Greenland lies about 2,9 million km&sup3; ice. If all that ice would melt and immediately spread over the entire ocean surface, how much rise in sealevel would this cause at the Dutch coast? a. Nothing changes. b. Between 2 and 3 m. c. Between 7 and 8 m. I'm quite sure I've got this right. I assume that 'at the Dutch coast' can be ignored. I forgot the formula for the surface of a sphere, so let's stretch the Earth to a cylinder and then flatten that out. That has a surface of about 40.000 x 20.000 = 800 million m&sup2;. The sphere will have a surface of about 3/4 of that (maybe even precisely; it rings a bell), so 600 million m&sup2;. The oceans span 2/3 of Earth's surface, so that's 400 million m&sup2;. 3 million m&sup3; / 400 million m&sup2; = 0,075 km = 7,5 m. Answer c. That was easy. :) Btw, doesn't the loss of the weight of the ice mean that Greenland will rise and surrounding land will fall? If that includes North-East Europe that would make matters even worse here. DirkvdM (talk) 08:37, 19 December 2011 (UTC)


 * I just did the math separately from your calculations. Start with 2.9x106km3 ice. Ice contains 0.9167g/cm3 water. So, you have 2.7x106km3 water. The surface of the Earth has about 3.6x108km2 water. If you assume that the area of the surface remains constant, you divide 2.7x106km3 by 3.6x108km2 to get 7.5m increase in the height. But, that requires a ridiculous assumption. See South Carolina Lowcountry. It is half of a U.S. state that is at (or below) sea level. Raise the sea level by 7.5m (around 25 feet), and it will all be below sea level - increasing the surface area by a great deal. I know it is insignificant compared to the size of the oceans, but that is one tiny part of the world. What about the entire coastline of every part of the world? What is required is a continual increase, about 1 meter at a time, and a recalculation of the surface area of the water for a calculation of how much is needed to fill in another meter of sea level height. -- k a i n a w &trade; 21:19, 21 December 2011 (UTC)


 * Interesting point. But I think it will make little difference. I haven't found a relief map that shows that much detail, but one world map shows that altitudes of below 200 m cover an area of at most 10% of the ocean surface (about half of which is in the Amazon and northern Europe). Below 8 m will probably be negligible. DirkvdM (talk) 15:20, 27 December 2011 (UTC)

Official answer The correct answer is B. If all this ice would melt and you take into account the density difference between fresh ice and salt water, you get a rise of the sea surface of just over 7 meters. But then you forget something very important. The ice mass on Greenland is so huge that it has its own gravitational field. This field draws water from the oceans to it. This may be viewed as sort of a permanent flood around Greenland. As if there is an extra moon over Greenland. The Netherlands is close enough to Greenland (3000 km) for this to have an effect here. If all the ice melts and its gravitational force disappears, that would lower the water level at the Dutch coast by 4,5 m. Together with the 7 m rise that gives a rise between 2 and 3 m.

In the tv show an image by GOCE was shown. This one illustrates the phenomenon quite nicely.

10.
A gray screen is filled with randomly placed black and white dots. With every new image on the screen the dots move a little to the right. We then see a fluent motion of the dots to the right. What happens to this movement if for every even image (number two, four, six, etc) the white dots are made black and the black dots white? a. We see the same movement, but at a much greater speed. b. We don't see any movement because your (sic) brain doesn't see an unequivocal (unambiguous?) movement. (Sorry about the crummy translation.) c. We see the direction of movement reverse. I'm fairly sure I've got this right. If we see any motion it has to be at the same speed and in the same direction because the distribution of the dots is random. So it has to be b, which indeed sounds plausible. I wonder what we would see if it were two recognisable images (faces would be effective) that move to the right and alternate. I think we might be able to see both images, or maybe just one (either) at the expense of the other. DirkvdM (talk) 08:37, 19 December 2011 (UTC)


 * Why not just do it? I did. Without the flipping on every even screen, movement moves to the right as expected. When flipping on every odd screen, it appears to wiggle left and right with a very general movement to the left. So, the most correct answer is that it wiggles. The next best answer is that it reverses direction. Neither is completely correct. -- k a i n a w &trade; 19:20, 19 December 2011 (UTC)


 * That's odd. It isn't like the spokes of a wheel moving the wrong way in a movie, because that happens because it is not a random pattern. The only thing I can think of is that when you look at a black-and-white pattern for a few seconds and then look at a white sheet you see the same pattern in reverse. But I don't see how that could cause this. It probably has something to do with the brain being confused and filling in what expects. DirkvdM (talk) 12:33, 20 December 2011 (UTC)

Official answer The correct answer is C. It is not yet clear to scientists why humans evolved such that our brains get a motion reversal of a contrast change. Your eyes 'shoot' dozens of pictures per second and each picture is compared by our brain to the previous one. Apparently it not only checks whether dark or light objects have moved, but also light and dark objects are compared with each other. Perhaps this additional information is used by the brain to see movement better. This reversal effect occurs not only in humans but also in many animals. Even houseflies have been put on a conveyor belts in front of a computer screen. They started walking the other way when they were shown contrast changing dots. It appears to be more than an optical illusion and really related to how animals and humans see motion.

In the tv show, they pointed out that this only works if you look at the whole picture. If you concentrate on a specific dot, you will see the correct motion.

11.
For riding a bicycle for the first time, you have a choice between an oldfashioned 'high bi' (v&eacute;locip&egrave;de) and a recumbent bicycle. On which of these two bicycles can you most easily maintain your balance? a. The high bi. b. The recumbent bicycle. c. Makes no different, equally difficult on both. A lower centre of gravity means a higher stability. And indeed getting onto a high bi will likely be tricky. However, I assume that they mean the stability once you're riding (at the same speed), and bigger wheels also mean a higher stability (never understood why, though), and my gut feeling tells me that is more important, so my guess is answer a. DirkvdM (talk) 08:37, 19 December 2011 (UTC)


 * This is complicated because you don't have clear values. You are on the right track. You want to know the gyroscopic effect of the wheels. The higher that is, the harder it will be to tip the bike over. Gyroscopic effect is based on many variables. In the simplest form, you need: Mass of the wheel, radius of the wheel, and rotational speed of the wheel. Increasing any of those will increase the gyroscopic effect. We know the old-time bike has a higher radius. It may or may not have a higher mass associated with the higher radius. However, it has a lower rotational speed because the larger wheel rotates slower to go at the same ground speed as a smaller wheel. So, the assumption is that all values will have about the same difference. When calculating gyroscopic effect, mass and rotational speed are multiplied into the formula. Radius is squared and then multiplied into the formula. So, a change in radius has much more effect than a change in mass or rotational speed. Therefore, I assume they want the answer to be that a larger diameter wheel will result in more gyroscopic effect, making the bike harder to tip over once it is moving. -- k a i n a w &trade; 21:27, 20 December 2011 (UTC)

Official answer The correct answer is A. Balancing on a bike is best compared with an inverted pendulum. The frequency of the pendulum is determined purely by the length of the rope. If it is long, the weight moves slower. This also works the other way around with a stick balancing on your hand. A long stick moves slower, so it is easier to make the necessary corrections with your hand to keep the stick centered above your hand. So a high bi is easier to balance than the low recumbent because you have more time to react.

12.
A 35 year old man transplants pubic hair to his head, to combat a fast advancing baldness, which is common in his family. What will he look like ten years later? a. Bald: the pubic hair will fall out, just like the head-hair. b. Hairy: the pubic hair is still there, but there is a big chance of curly hair. c. Hairy: the pubic hair is still there, and it has assumed the shape and colour of the head-hair. Indirect reasoning: if c were the answer, then wouldn't this be commonplace? Or is it that there isn't enough pubic hair? And if it's a because it's heredetary, then might a donation by a non-reliative help? (The grossness increases.) Note, though, that the fact that it's common in his family doesn't necessarily mean that that is the cause of his baldness. It's just an indication. My (fairly ramdom) guess is b. DirkvdM (talk) 08:37, 19 December 2011 (UTC)


 * I asked a dermatologist at lunch. He said that you can transplant pubic hair to your head, but it will always look thinner than the rest of your hair, resulting in always looking like you have thinning hair. He said it will not thicken and blend in with the hair currently on your head. Also, years later, the bald spot will continue to grow. So, you'll have a patch of pubes on top of your head, a bald ring around that, and then your normal hair. So, that's one guy's opinion - not really mine since I know next to nothing about hair transplants. -- k a i n a w &trade; 21:30, 20 December 2011 (UTC)

Official answer The correct answer is B. Not the conditions on the scalp, but the genetics of the transplanted hair follicle determines how the hair grows. Pubic hair stays pubic hair, also on the head: it retains its shape and color and it does not fall out. In men with hereditary baldness, the head hairs have a genetic oversensitivity to the hormone dihydrotestosterone (DHT), which is formed from testosterone. DHT makes the follicles wither. Pubic hair does not have this genetic oversensitivity, so the transplanted hair continues to grow, but the chance of curls is quite big.

13.
When you make a tea towel wet it gets darker in colour. When you let it dry, it gets lighter again. What causes this colour change? a. The water acts like a sort of glass fibre, as a result of which the light penetrates more deeply into the material. b. Because the refractive index of water lies close to that of textile, the scattering decreases. c. Water absorbs more red and green light than textile. Before reading the answers, I assumed it would be because the scattering decreases. I don't see why the refractive indices being close together has anything to do with it. Then again, that would mean it's more mirror-like, which would mean that some parts will 'flicker', and I've never seen that. Water being blue-ish suggests the reasoning of answer c. But then it would (also) turn blue. So I put my Sherlock Holmes cap on and say it's answer a. Water conducts light better, so that is even plausible. DirkvdM (talk) 08:37, 19 December 2011 (UTC)


 * I have to go with (a) on this, but the reasoning is (b). The refractive index of water is about the same as most fabrics. So, light gets into the water and is (for lack of a better word) tunneled into the fabric. Light can, therefore, pass through the fabric easier. If you wet a spot on a shirt and hold it up between you and the light, you will see that the wet spot is lighter, not darker. Further, this effect is very important when it comes to wet T-shirt contests. If the light couldn't pass through the wet fabric easier, there would be little difference between a wet and dry shirt. -- k a i n a w &trade; 21:38, 20 December 2011 (UTC)

Official answer The correct answer is B. How light or dark an object looks like is determined by the amount of light scattered by the object. The more scattering, the brighter the object appears. The degree of scattering depends in part on the difference in speed of light between the environment and the object. In vacuum it is always constant, but in textiles it is much slower than in air. When there is water around the fibers, the difference in speed between the environment (the water) and the fiber is much smaller. As a result, less light gets scattered and is the subject looks darker. A measure of the speed of light in an object is the refractive index. The refractive indices of water and textiles are close together, so the wet towel is darker.

In the tv show they also showed what kainaw said, that as you hold the towel agianst the light, the wet spot looks lighter because more light passes through it. They also demonstrated a little 'miracle'. A glass cup was places inside a bigger glass cup. Then an oil with a refractive index close to that of the glass was poured into the smaller cup. It remained visible. But as it poured over the rim, it started to miraculuously 'disappear' until it was fully immersed and invisible (except for some writing on it).

14.
You have 3 boxes with pralines. One contains 2 white pralines. One contains 2 brown pralines. And one contains a white and a brown praline. You randomly choose one of the three boxes and then from that you again randomly pick one of the two pralines. The praline is white. What is the chance that the other praline in the chosen box is also white? a. 1/3 b. 1/2 c. 2/3 I'm quite sure I've got this right. It's simpler to forget about the boxes and present this as 6 pralines, 'bonded' in pairs as described (doing it in two stages only unneccesearily complicates matters, which of course is why they presented it that way). You pick a praline that turns out to be white. This can be one of the three white ones. Two of these are bonded with a white praline and one is bonded with a brown praline. So the chance of it being bonded with another white praline is 2/3. Answer c. DirkvdM (talk) 08:37, 19 December 2011 (UTC)
 * I disagree. If you keep the idea of the three boxes, once you have picked out a white as the first, you know it cannot have come from the box with two browns. Therefore, you now have two possible scenarios. Either you picked it from box 1 (WW) or box 2 (WB). If it was from box 1, the next one you pick will be white. From box 2, it will be brown. Therefore the possibility of the OTHER praline being white is 1/2. - Cucumber Mike (talk) 18:25, 19 December 2011 (UTC)


 * The answer is C (2/3 or 66.6% of the time). For me, it is easier to just run a simulation (which spits out 66.6% of the time). -- k a i n a w &trade; 19:31, 19 December 2011 (UTC)


 * Now that I have a break, here's why it is 2/3... Assume you do 6 attempts. 2/6 attempts will probably end up getting the BB box. So, we don't care about those at all. So, we are limited to 4 picks we care out. Out of those 4, 2 will pick the BW box. Out of the 2 times you pick the BW box, you will 1 time pick the B and 1 time pick the W. We don't care about the 1 time you pick the B. We are down to 3 picks overall that we care about. 1 of those 3 comes from the BW box in which you pick W and the other is B. 2 of those comes from the WW box where you pick W and the other is W. So, 2/3 times you pick W and the other is W. -- k a i n a w &trade; 19:56, 19 December 2011 (UTC)


 * I agree - it is C 2/3. The flaw in Cucumber Mike's reasoning is that once you know you have chosen a white praline, it is twice as likely to have come from the WW box as from the WB box. Gandalf61 (talk) 10:48, 20 December 2011 (UTC)

Official answer The correct answer is B. This question is an application of the famous paradox of Joseph Bertrand. He wanted to show how important it is to count correctly. The correct answer is 2/3. There are three options to pick a white chocolate. The box with the two dark chocolates can be ignored.

In the tv show the explanation was more complete; for 2 of the 3 options the other chocolate is white. They also demonstrated it with the audience who had such boxes. The number of people who picked two chocolates of equal colour was much bigger than the rest. And they also mentioned that this is an example of combinatorics.


 * The audience demo makes me think of another way to explain this. They were asked to raise their hands if they had picked the same colour, be it white or brown (which is basically the same). Since there are 2 such boxes, the chances are 2/3. DirkvdM (talk) 13:14, 28 December 2011 (UTC)

15.
A ship that transports drinking water lies waiting in a large sea-lock. Through a hole in the ship seawater streams into the ship. To prevent the ship sinking, the crew pumps drinking water into the lock. Just as much water streams into the ship as the crew pumps away. The water level in the lock: a. rises. b. falls. c. remains equal. I'm quite sure I've got this right. The weight of the water that a ship displaces is equal to the weight of the ship (Archimede's bath tub). And salt water is heavier than fresh water. So as water is exchanged, the water in the lock gets lighter and the (water in the) ship gets heavier. Both of these mean that more lock-water has to be displaced to keep the ship afloat. So the ship goes down and the water level in the lock rises. (Of course, this is assuming that 'just as much water' refers to volume, not mass.) I wonder, though, why the question specifies that it is a large lock? Would it be different if it were small? Does any capillary effect maybe depend on the salinity of the water? It would have to be an extremely tight squeeze, though. :) DirkvdM (talk) 08:37, 19 December 2011 (UTC)

Official answer The correct answer is A. Seawater has a higher density (1030 g/l) than fresh water (1000 g/l). The density determines the buoyancy - the higher the density, the easier something floats. The salt water in the lock is mixed with the fresh water from the ship. This reduces the density of the water in the lock, reducing the buoyancy. Furthermore, by pumping the water in the ship is gradually replaced by seawater. This increases the mass of the ship slightly. So the ship is heavier and the buoyancy of the water in the lock decreases. Both effects have a negative impact on the draught of the vessel: the ship sinks in deeper, so the water in the lock rises.

Results
Of the answers I sent in I got 16 right. The ones I got wrong were 2 (swimming pool), 3 (Facebook), 9 (Greenland ice) and 10 (dots on screen). I should have gotten 3 right. Shame on me. 10 was more a matter of knowing than of reasoning (it is even puzzling for scientists). Something similar for 9, but to a much lesser extent. I contest the answer for 2. Not all factors were taken into account, especially the effect of neighbouring swimmers - they only looked at the depth. Of the rest of the public only 2 got all answers right (the winner got second prize last year). The rest got on average 6,3 answers right, same for men and women. The questions that got most wrong answers were 2 (swimming pool) and 13 (wet towel).