Seeing how fast a vibration travels through a solid medium.
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Teachable Topics
- sound
- vibration
- phonons
Theory
The speed with which a physical vibration moves through a physical medium depends upon a great many factors. Among these are the medium's physical dimensions, its density, its temperature, etc. Once a vibration is set in motion, it takes a collective motion ff the atoms within the media to transfer the energy across the whole expanse.
That transfer takes time. And often will involve technical challenges such as echos and outright dissipation, where the amplitude of vibration falls below your equipment's ability to measure.
Apparatus
- digital oscilloscope with a minimum of two channels
- piezo discs with electrical connections (often called "buzzer" discs)
- meter stick
- tape
- hammer
Procedure
- Connect two separate piezo discs to separate channels on a multi-channel oscilloscope.
- Test the discs by pressing them and watching for the corresponding signals on the scope. Adjust the settings as appropriate to make the signal clear and visible.
- Tape the discs to the medium under investigation at a measured distance.
- Set the oscilloscope trigger to a level just above its nascent zero signal and set the measurement to "one shot" or its equivalent.
- Arm the oscilloscope and then start a vibration impulse with a hammer as near to one of the discs as you can. Be careful not to hit the disc directly.
- Once your scope triggers, adjust the setting and use the cursor functions to read the time difference between the two traces.
- The speed of the vibration is the distance between the discs divided by the elapsed time.
Safety
- This experiment presents no safety hazards.
