11. Nature and Production of Sound Waves -

How sound is generated through vibrations, and its fundamental properties as a longitudinal wave.

Sound waves are mechanical, longitudinal waves comprising compressions and rarefactions.

When you hit the skin of a drum, it starts vibrating, moving back and forth very quickly.
These vibrations squeeze and stretch the air in front of the drum, disrupting the surrounding air molecules.
The series of squeezes and stretches produces compressions (regions of high pressure) and rarefactions (regions of low pressure), which travel through the air as sound waves.
Sound is produced by vibrating sources placed in a medium (such as air, water, or solids).
A vibrating object in the medium causes alternating compressions and rarefactions, which carry the sound energy further away through the medium.
Sound is a form of energy related to the vibrating motion of molecules.
This energy travels from one point to another as a wave.
Example: A guitar produces a musical note when its string vibrates, creating sound waves in the air.

What it means:
When a sound wave travels through a medium (like air, water, or a solid), the particles of that medium vibrate back and forth in the same direction that the wave is moving.
Imagine this:
Think of a slinky spring lying on a table.
- If you push and pull one end of the slinky forward and backward, you see compressed regions (coils close together) and stretched regions (coils far apart) moving along the spring.
- This is exactly how sound waves move through a medium.
In Physics Terms:
- These waves are called longitudinal waves because the oscillation (vibration) of particles is parallel to the direction of wave propagation.
- The compressed regions are called compressions (high pressure, high particle density).
- The stretched regions are called rarefactions (low pressure, low particle density).
Why sound behaves this way:
- Sound needs a medium (air, water, metal, etc.) to travel.
- In air, the particles are normally randomly spaced.
- When a vibrating source (like your vocal cords or a speaker cone) moves forward, it pushes air particles together (compression).
- When it moves backward, it pulls particles apart (rarefaction).
- This push-pull pattern travels from particle to particle until it reaches your ear.

The compressions and rarefactions in sound waves are due to slight changes in air pressure.
Compressions: Regions where air pressure is slightly higher than the surrounding air pressure.
Rarefactions: Regions where air pressure is slightly lower than the surrounding air pressure.
This continuous rise and fall in air pressure occur as long as the sound source (e.g., drum) keeps vibrating.
The regions where sound travels through air can be visualized as a repeating pattern of high and low-pressure zones.