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Re: speed of sound experiment



At 06:08 AM 9/15/97 -0700, Dave wrote:
John Gastineau wrote:

I did a variation on a speed of sound experiment tonight that I thought
I'd share. The basic experiment is to use a microphone and a CBL, MBL, or
memory oscilloscope to record the echoes of a short sound as it bounces
back and forth between the ends of a packing tube.

I'd really be interested in using such an experiment with my class.
Where can I find details on the set-up? Ant reason it couldn't be done
with lighter than air gases and an inverted tube?



There's not a lot to it.

Take a cardboard packing tube such as holds a dynamics cart track or a
poster, ie, maybe a meter long and 10 to 15cm diameter.

Place a microphone at one end. Set up MBL/CBL to take data for 20 ms,
triggered mode. _gently_ tap the tube end to both trigger the mic and to
send a pulse bouncing back and forth within the tube. Both ends can be
open.

It WILL take a bit of futzing around to learn how to make an appropriate
sound. The sound pulse must not be bright, exciting higher frequencies, it
must not make the tube resonate, and it must be short. You'll figure it
out, though.

You'll get a string of pulses (all non-inverted for two open ends)
corresponding to the sound returning to the end with the mic. If you close
one end, the pulses are inverted each trip.

Give it a try with lighter gases--I don't keep helium in my kitchen, just
CO2. (Although I have heard of beverage uses of nitrous oxide...) You'll
never get a pure fill of the other gas, but it's neat just to see that the
speed is different.

JEG

__________________________________

John E. Gastineau gastineau@mindspring.com KC8IEW
900 B Ridgeway Ave. http://gastineau.home.mindspring.com
Morgantown WV 26505 (304) 296-1966