1. Initial Impact:
When the pencil tip strikes the desk, it causes a mechanical disturbance, creating a back-and-forth vibration in the desk.
2. Compression Waves:
These vibrations generate a series of compression waves in the surrounding air. As the desk vibrates, it pushes air molecules closer together, creating areas of high pressure, or compression.
3. Rarefaction Waves:
Following the compression, the desk's motion changes direction, causing the air to return to its original state. This creates zones of low pressure called rarefaction waves.
4. Alternating Cycles:
The vibration of the desk produces a pattern of alternating compressions and rarefactions, which form sound waves. These sound waves travel through the air at a fixed speed, about 343 meters per second (768 miles per hour) at room temperature.
5. Transfer of Energy:
As sound waves travel through air, they cause successive air molecules to vibrate and pass the mechanical energy from molecule to molecule. This chain reaction of vibrations enables the sound to propagate through the air.
6. Reception and Perception:
The sound waves eventually reach the student's ears. When the sound waves enter the ear canal, they cause the eardrum to vibrate in sync with the alternating compressions and rarefactions. This vibration is transmitted to the inner ear, where it is converted into electrical signals and interpreted by the brain as sound.
In summary, when a student taps a pencil on a desk, the vibrations created by the impact set up a series of compression and rarefaction waves in the air, which propagate outward and allow us to perceive the sound.