Effect of Thermal Expansion on the pitch of Steel/Bamboo Flute and Guitar

Effect of Thermal Expansion on the pitch of Steel/Bamboo Flute and Guitar
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The present experiment was prompted by @ravi31 who asked certain questions regarding effect of various conditions on the pitch of a flute made out of a straw or paper.

However, I thought of creating this thread to share my experimental observations (not very scientific though) with other and prompt them to do something similar which could help us to come to a conclusion.

“DON’T TRY THIS WITHOUT ADULT SUPERVISION”

The Experiment

Aim: To prove the assumption that thermal expansion would affect the pitch of Guitar more as compared to a Bamboo Flute and a homemade Steel Flute.

Apparatus: A Guitar, a Bamboo Flute, a homemade Steel Flute, some clay, a mobile phone, a hammer, a screwdriver, a hand drill, a steel pipe to make the steel flute, a measuring tape, a hacksaw and a hair dryer.


Some of the apparatus. Though the Axe has been put there for dramatic effect only :wink:, it would work as a hammer as well.

Apps used:
gStrings – for measuring the pitch of the guitar.
Frequency Counter – for measuring the pitch of the Bamboo as well as the Steel Flutes.

Procedure:

First, Make a Steel Flute.

  • Cut the steel pipe into a 15-inch section (so that it could fit in a freezer, if you have a bigger/smaller freezer you can increase or decrease accordingly).
  • Drill a hole about 5-6 mm in diameter 1 inch from one end using a hand drill. Please don’t use a power drill. Its RPM might be just too high. Alternately you can make this hole using a screwdriver as well.
  • Block the passage of air at the side of the hole just made by using clay.
  • Viola! Your flute is ready. No other holes are required as we have to test the flute at one pitch only. Other holes may lead to leakages and possibility of errors.

Now the fun part:

Data:

Bamboo Flute:

Steel Flute:

Guitar:


Findings:

Bamboo Flute: Hardly any noticeable change in the pitch. Just a drop of 0.1 Hz only.

Steel Flute: Marginal change in the pitch. It’s so minute it cannot be perceived by the human ear. A drop (instead of increase which it should have) of 0.1 Hz while frozen and a drop of 0.2 Hz when heated.

Guitar: Clear change in the pitch. A drop of almost 2 Hz. It may not be perceived by an average person but an average guitarist or any average musician can easily tell the difference.

Q.E.D. Thermal expansion will have more effect on a stringed instrument that a Straw/Bamboo/Steel Flute.

Possible Errors:

  • Temperature was not accurately measured. It has been described as NORMAL, HOT or simply FREEZING, which, by the way, is not very scientific.
  • In case of the Steel Flute the is a marginal drop in the pitch instead of the expected increase in the pitch while it has been frozen. It could be due to the different thermal properties of the steel used and the clay used to block one end.

Important Notes:

“DON’T TRY THIS WITHOUT ADULT SUPERVISION”

Pics & Videos and Assisted by: : Miss Pritika Siyan @Pritika

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This is a very inspiring effort! Thanks for sharing your notes and observation. Also, the results are quite intriguing.

This also pushes us to explore what could be the possible explanation for this.

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It’s quite simple though :stuck_out_tongue_winking_eye:
The steel flute may show a similar results if it’s length vs diameter ratio is same as the string.
You see, considering the string has a diameter of about 2mm and length of 1 m.
The ratio turns out to be
1:500

That means if we need to have a similar effects, the flute should have the same ratio. Considering the diameter of flute to be 20 mm, it’s length should be 20×500 = 10000mm = 10m!
It would not be possible to play such a flute😢!

Hence , the effect of variation of temperature will always be more on stringed instruments.

We can try this with Sitar, Tanpura, etc that have metal strings. Violins, cellos, happen to have organic or synthetic strings. They will produce different results.

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