(1)
On Museum Hill in Santa Fe, there is a labyrinth paved with green
and tan pavers, surrounded by a low circular wall. Of course,
this wall produces nice echos when you stand in the center.
I noticed that when you clap your hands, the echo contains a clear note
(in fact it is a chirped note). I suspected that it had to do with the
size of the pavers, so I recorded a few claps with my cellphone.
Play the sound file:
On the right is the frequency spectrum (of the first echo),
made with
Audacity.
There are three clear peaks in the spectrum, the biggest one at 2.9 kHz.
Multiply that by the speed of sound, and you get a wavelength.
The corrugations in the brick pavement favor frequencies that match their spacing.
5 brick take up 59 cm, for 11.8 cm per brick.
Perfect match!
(2)
In 2023, we were in Yucatan for the
annular solar eclipse, and
we visited the great pyramid of Chitzen Itza.
We noticed people standing at the center line facing the steps, a fair
distance away, and clapping to produce a nice echo from the stairs,
which had a clear note in it.
You are not allowed to climb these stairs.
A video was taken by our fellow travelers Jim and Elias, I used
Shotcut (a free video editor)
to split off the audio, an used
Audaciy (a free
audio editor) to make the spectrum.
The peak is at 575 Hz, which gives 59.1 cm for the step width.
Correcting for
the temperature (~30°C) and the humidity (~80%) increases
this by a few percent.
The higher frequencies are multiples (×2 and ×3) of the
base frequency
The next day, on the backside of a pyramid Uxmal, there were some
impossibly steep stairs. Here we could come
close enough to take a measurement. I measured a step width (my hand spans 22cm),
so the step is 19.3 cm.
Links:
xxx
Sep 2022 and Oct 2023
Internal combustion
A soda bottle, 1/2 teaspoon of rubbing alcohol, and
a hand-held Tesla coil
Click to play the movie →
Links:
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added Jun 2024
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