Resonance and a tuning fork 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.
 A: 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.  
A: 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.
