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I carried out this experiment in class:

I struck a tuning fork with a hammer. The sound lasted for some time.

However, when I connected the tuning fork onto a wooden sounding box, the sound lasted for a few seconds (much shorter than the previous case)

But why is that? I know the reason is because of resonance but can someone please explain the reasoning behind these observations with detail.

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    $\begingroup$ Was the sound louder after connecting the fork to the sounding box? Consider this along with the principle of conservation of energy. $\endgroup$
    – BMS
    Apr 17, 2014 at 7:10
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    $\begingroup$ @BMS: The sound was louder. So is it because the box actually resonates and thus large amount of energy from the tuning fork is transferred to the box and due to this transfer, the tuning fork lost energy quickly? $\endgroup$
    – Eliza
    Apr 17, 2014 at 12:13
  • $\begingroup$ Was the sound louder in all the directions or just in a preferential one? $\endgroup$
    – DarioP
    Jun 20, 2014 at 13:20

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A vibrating tuning fork contains a finite amount of vibrational energy. As it generates sound waves, this vibrational energy is transferred to the air as sound waves. As this energy is used up, the tuning fork grows quieter until it can no longer be heard.

A sounding board is designed to increase the amount of sound produced by a vibrating item (usually a string.) The increase in sound is offset by an increase in energy transference. Because more energy is leaving the tuning fork as sound, the tuning fork grows quieter, faster.

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The reason why the tuning fork creates a sound is because it makes the air molecules around it vibrate, which means that there is a longitudinal sound wave created. If I understand correctly, the bottom of your tuning fork was placed into a wooden block and then struck with a hammer. The wooden block does not actually resonate (the frequency of the tuning fork would have to match the wooden block's natural frequency for that), it instead serves as a dampening device for the tuning fork and therefore damps the tuning forks displacement from the bottom. This just means that the tuning fork's maximum displacement decreases a lot faster with the dampening of the wooden block, and the sound therefore lasts for a shorter time.

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  • $\begingroup$ ok... this explains why the sound lasted for a shorter time. Also, the sound was louder when the tuning fork was placed on the sounding box... so i guess the frequency of the tuning fork did match the wooden block's natural frequency $\endgroup$
    – Eliza
    Apr 17, 2014 at 12:11

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