Impossible Heights: Newsletter Challenge (August 2012)

AHH... what thread are you on?????

Huh?

We all know the debate about whether a tree falling in the forest really makes a sound if nobody hears it, but that its very height is attributable to psychoacoustics? How come I never thought of that?

"And the answer is:

When a sound signal is received by a linear system (linear response) only the fundamental tones (the ones actually present in the sound) is sensed or transmitted. However, if the system exhibits non-linear responses, not only the fundamental tones are sensed and transmitted, but also the system reproduces the harmonics of each one of the tones present in the sound. This means that the non-linear system reproduces the sums and differences of the whole number multiples of the fundamental frequencies. It happens that the system formed by the ear and brain is actually a non-linear system, so we hear a low fundamental tone (like in human speech) and all the harmonics produced by the system, including the large wavelength of the bass tones."

Oops! It looks like the answer to last month's question was posted by mistake. The correct answer is now available for August's challenge question. Sorry for the confusion.

"The correct answer is now available for August's challenge question."

Where?

http://cr4.globalspec.com/blogentry/20610

That is certainly a decent explanation, and the mechanism I tend to believe is dominant.
However, if CR4 challenges are about anything, they are about developing a proper understanding. On this basis the explanation needs fleshing out, as there are apparent difficulties. The principal one relates to the way trees seep when injured. The difficulty is that there don't appear to be any membranes between the roots and the leaves - which implies that the osmosis would be supporting a continuous 100m column. This leaves (qv) us with a problem: how come that trees all leak slowly when punctured, and the rate is apparently independent of the height at which we make the hole? (We might expect the contribution from below to depend strongly on the position).

The other problem relates to the explanation that you reject: even though the tubes in the tree are too large to support capillary action, this does not in fact mean that capillary action cannot be responsible. For example, 20-nm wide slits would readily pull the water up the requisite distance, and there is no reason the meniscus could not vary in radius so that you have a different (and supportable) equilibrium at each height. The apparent issue with capillary action is that we would not expect the tree to leak at all. On the other hand, there could always be evaporation/condensation into a separate circulatory system that ran continuously from top to bottom of the tree.

So please - more meat to the explanation.

Thanks

1010T

I'll contact the creator of the question and ask him to get back to you.

Ha !

It's continuing a grand tradition - the occasional 'are we awake, boys and girls ?' (intended or not) is hootingly funny. There have been a few bloops that lay dormant for weeks. Many a Challenge question has never had universal agreement (the 'bouncing balls' question still gives me nightmares - detailed explanation from Phys and I still don't get it . There would be no fun if I did).

Is this an answer to some other thread?

If not, please explain how this relates to water transport up a tree...