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Donnie B.
2004-Dec-06, 11:21 PM
Another potentially endless thread, if it catches on...

Describe something that is indisputably true but seems utterly counterintuitive. Followup posts must give a reasonable and reasonably accurate explanation for the phenomenon, and may then post the next perplexing puzzle.

Joke answers are okay, but don't earn you the right to post the next puzzle!

To start it off:

How can an all-wooden ship ever sink, even if it's full of water?

Musashi
2004-Dec-06, 11:25 PM
I imagine if the wood gets waterlogged.

Donnie B.
2004-Dec-06, 11:28 PM
I imagine if the wood gets waterlogged.
Sorry, can't accept that answer. The Vasa, for one, sank on its maiden voyage... no chance to get waterlogged.

Nicolas
2004-Dec-06, 11:31 PM
All wooden ships, like hollow trunks from light wood, can't sink. Sea ships have stones down under to give them stability. They need teh air inside the hull to keep them floating. Completely wooden rafts (like cliché survivors wreckage rafts) won't sink. But large ships have these stones, cargo, possibly coal, metal nails, pins, anchors, bars, cannons. Anything lighter than water can't sink. But if it's trapped around enough things heavier than water...blub

Donnie B.
2004-Dec-06, 11:46 PM
All wooden ships, like hollow trunks from light wood, can't sink. Sea ships have stones down under to give them stability. They need teh air inside the hull to keep them floating. Completely wooden rafts (like cliché survivors wreckage rafts) won't sink. But large ships have these stones, cargo, possibly coal, metal nails, pins, anchors, bars, cannons. Anything lighter than water can't sink. But if it's trapped around enough things heavier than water...blub
Not to mention copper sheathing, caulking, etc.

And we have a wiener! Post your puzzle, Nicolas.

Moose
2004-Dec-06, 11:47 PM
Take your pick:

1) If its spaces contain enough ballast to increase it's total average density beyond that of sea water. (Anchors, keel ballast, rigging, cargo, etc.)

2) If the wood is itself naturally denser than sea water.

3) If the wood, when saturated with water (in the sense of porous wood having it's air forced out), becomes denser than sea water.

4) (Bermuda Triangle hypothesis) If an undersea-bed gas pocket releases directly beneath a wooden boat, the "sea water" becomes less dense than the average density of the boat.

[Dang. *snaps fingers* Missed it by that much.]

Donnie B.
2004-Dec-06, 11:51 PM
Good answers anyhow, Moose :D

Parrothead
2004-Dec-07, 12:29 AM
Yeah, but the Vasa sank due to its construction IIRC. It was too high, the ballast was off, cannons too heavy, it tipped after launching. I can give more detail, after digging out a book on its architecture that I bought at the Vasa museum in Stockholm. All I can say is, what an impressive piece of work!

edit: I should take the time to fully read a thread instead of quick skims, amazing how one can miss details (such as someone already providing an answer). :oops:

Musashi
2004-Dec-07, 01:19 AM
Just for clarity, I didn't understand that the answer had to solve all potential circumstacnces. I guess it is more of a nitpick, but perhaps the questions/puzzles should be more specific in the future?

Moose
2004-Dec-07, 02:56 AM
Musashi, I don't think you have to list all of em (I'm sure there are others I missed), but I wasn't sure what Donnie B was looking for, so I wanted to be sure to cover as many bases as possible as I thought of them.

I think I should have hurried instead. :P

Nicolas
2004-Dec-07, 06:48 PM
OK I'm thinking about my mystery right now. Sorry for the delay, it was night overhere.

Nicolas
2004-Dec-07, 07:08 PM
Rather technical one my brother asked himself:

In radio speakers, the sound is carried as an electrical current wave, translated into a soundwave of the same form through the speaker movement. Low sounds are waves with long length, high pitched sounds are waves with short lengths. The question is: how can an analog wave signal carry information about a high note played over a long low note? at (what appears to be) the same time? I mean, how is the short wavelength added to the long one in one waveform without resulting in some "in between pitched" sound? To avoid misinterpretation: this counts for single cone speakers as well.

ZaphodBeeblebrox
2004-Dec-07, 08:19 PM
They use different channels, so that the Speakers can follow the Electrical Impulses, more precisely.

Nicolas
2004-Dec-07, 08:20 PM
How do you mean, different channels in one analog electric signal travellnig through one cable?

Donnie B.
2004-Dec-07, 08:26 PM
Well, I know the answer (as an electrical engineer who has worked in the audio industry in the past), but I'll stand aside so another puzzler can take a shot... :D

Nicolas
2004-Dec-07, 08:29 PM
On top of this I also wonder how one cone can vibrate in such a way that it generates a continuous low tone with a high one on top, which is the same problem (because I was talking about analog signals). The only thing I can think about, is some kind of sampling, so a very fast altering between different waves, but this has some impractibillities I think (this is more of a solution for the digital domain).

Ut
2004-Dec-07, 08:58 PM
Well, of course there's going to be some issues with not getting the proper sound out. That's why you rarely see a stereo with only one speaker, or only one kind of speaker. It's also why standard car stereo systems sound like garbage.

IIRC, you can use two different magnets to produce high and low frequency waves fron a single speaker cone. This would have huge disadvantages, though, in that it would severely limit the range of the speaker. I can't imagine sound quality would be all that great, either.

Usually, a single "speaker" will have two or three different cones in it, though, for high, midrange, and low tones.

Different signals can be sent, overlapping, through a single wire by using different carrying frequencies. Just like different radio stations can all play at the same time, even though you only pick up one at a time. You just make your receiver sensitive to only one channel.

Weird Dave
2004-Dec-07, 09:22 PM
Rather technical one my brother asked himself:

In radio speakers, the sound is carried as an electrical current wave, translated into a soundwave of the same form through the speaker movement. Low sounds are waves with long length, high pitched sounds are waves with short lengths. The question is: how can an analog wave signal carry information about a high note played over a long low note? at (what appears to be) the same time? I mean, how is the short wavelength added to the long one in one waveform without resulting in some "in between pitched" sound? To avoid misinterpretation: this counts for single cone speakers as well.

This works because loudspeakers, microphones, and all the electrical gumph between them, are all linear devices (at least at normal volumes). That is, you can add two waves of different frequencies together, and the sum will act exactly like the two waves separately. A microphone records two (or more) notes at the same time, the electrical signal travels to your loudspeaker (via whatever method), and the louspeaker plays a noise that sounds exactly the same as if there two loudpeakers, each playing a separate note.

Your ear contains myriad tiny hairs that each vibrate at their own frequency. They are arranged so that the high-frequency ones are at one end of the cochlea (part of the inner ear) the lowest frequency hairs at the other, and the middle frequencies ranged in-between. Each hair detects its own frequency, which is unaffected by any other frequency present (this is what linearity is all about). So those two notes are each detected by the same parts of the ear that would detect each one by itself.

Note a couple of interesting exceptions. First, if the two notes are of very similar frequencies (f and F, say), they will add together linearly as normal. However, we can also imagine that the new sound is composed of two very different frequencies, the average (f+F)/2, and (half of) the difference (f-F)/2. These two waves are multiplied, not added. This gives a high-pitched note that oscillates at a very low frequency, so low that you can hear it warbling. This is known as "beating". Secondly, if the two notes are exact multiples of each other (e.g. one is twice the frequency of the other) you may not hear them separately. Instead, you hear a note at the lower frequency that has a different quality. The higher note is now a harmonic, and this is why instruments like guitars and pianos sound different.

The length of this post should alert you that I'm trying to avoid revision.

[Edit after seeing Ut's contribution]

I'm assuming that the two notes are similar enough that the loudspeaker plays them both at the right volume. However, a big bass speaker can't vibrate fast enough to produce high-pitched notes, so different ranges of frequency are usually split up electronically and sent to different speakers. The splitting-up is a relatively simple matter thanks to linearity and involves making "resistors" (actually combinations of resistors, inductors and capacitors) whose resistance is a function of frequency. [I think. I'm no hi-fi expert, so may have a few details wrong].

Nicolas
2004-Dec-07, 09:29 PM
I give Weird Dave the credit for the answer. His explanation of the added waves sounding the same as the original multiple notes made it clear. The mistake in my reasoning was that I mistakenly thought that the sumation of "simple" waveforms would be 1 "simple" wave. Don't ask me how, as I am familiar to both oscillator readouts and things like Fourrier series... :oops: oops

Up to the next mystery!!!

Grey
2004-Dec-07, 09:36 PM
If it's an analog signal, you don't have to sort it out. Let's ignore for a moment that good speakers are really composed of several speakers together in one housing, and just imagine the simplest case of a speaker with a single diaphragm and driver. If you have two pure tones of differing frequencies, they'll combine to produce a signal like this:

http://www.physicsclassroom.com/Class/sound/u11l3a2.gif

Where the red and blue lines show the separate tones, and the green line shows the combined result. This is really just the same as the pattern of air compression and rarefaction that the original sound produces.

So in producing the analog signal in the first place, you've just converted that complex pattern of air pressure changes into an electric signal. You send the combined signal, the diaphragm oscillates in a weird way and reproduces that pattern of air pressure changes, and your brain does the hard work of sorting that out into you perceiving a high tone and a low tone together.

Adding in any number of other sounds makes the wave pattern more complex, but the sound system never has to bother trying to split the individual sounds out, it just reproduces the whole mess together.

[Edit: Rats, way too slow! :D ]

Weird Dave
2004-Dec-07, 10:11 PM
Why does a supposedly intelligent person such as the BA insist on believing, and spreading, the fantasy that people have walked on the moon, in spite of all the scientific evidence to the contrary? :roll: Perhaps he's just jealous that the Zetans aren't talking to him...










8-[








:wink: :D
Sorry, but I can't think of a decent proper question. Somebody else can have a go.

Nicolas
2004-Dec-07, 10:16 PM
Grey: too late, but thanks anyway. Your answer was as clear and on the spot as Weird Dave ones. So as Dave doesn't find a mystery, you and Ut (for an answer that didn't really answered the question but was a good effort and not wrong an sich) can give us a mystery!!

Grey
2004-Dec-08, 12:14 AM
...you and Ut (for an answer that didn't really answered the question but was a good effort and not wrong an sich) can give us a mystery!!
This isn't really quite right for the thread, but it's the only thing that keeps coming to mind, since I discussed this with a student just recently. Perhaps Ut can do better.

You're in a boat, floating on an exceptionally calm lake. You find the perfect spot for fishing, check the depth, and then hurl the anchor out of the boat into the water, where it of course sinks to the bottom. After the waves die down, you take another depth sounding (with an impossibly precise measuring device, of course :) ). Has the water level changed? If so, how, and either way, why?

Ut
2004-Dec-08, 12:20 AM
Aye.
The water level has gone down.

While in the boat, it's displacing the volume of water which has a mass equal to the mass of the anchor. Since the anchor sinks, this volume must be greater than the volume of the anchor. So, by throwing the anchor into the water, less water is being displaced.

Grey
2004-Dec-08, 12:21 AM
Aye.
The water level has gone down.

Correct. So by any measure, it's your turn next.

Ut
2004-Dec-08, 06:47 AM
Nope. After several hours of pondering, I'm coming up with an uncreative blank.

I'm going to throw this one out to the peanut gallery.