1. Sounds Good

2. Mechanical Waves – Interacting Particles
A sound wave is created by vibrating objects and the wave passes through a medium.
The “medium” (i.e., the material through which the disturbance moves) can be thought of as a series of interacting particles.
A disturbance that travels through particle-to-particle interaction is known as a mechanical wave.
Because a mechanical wave requires particles to carry the disturbance, mechanical waves cannot travel through a vacuum.

3. A Slinky™ as a Mechanical Wave
A disturbance is created by a back-and-forth movement of the first coil.
The first coil becomes disturbed and begins to push or pull on the second coil, displacing the second coil from equilibrium.
The second coil pushes or pulls on the third, and so on.
The disturbance travels through the Slinky so that the energy that was originally introduced in the first coil is transported along the medium from one location to another.

4. Sound cannot travel in a vacuum!

5. Sounds Waves are Mechanical Waves
Sound waves need a medium to travel through—air, water, steel, etc.
Sound waves must have an original vibrating source that disturbs the first particles in the medium.
A tuning fork, for example, vibrates back and forth and disturbs the surrounding air molecules.
The tuning fork can be connected to other surfaces and cause them to vibrate also— which in turn causes more air particles to be disturbed and produce a louder sound!

6. Air is made of different molecules.
Sound travels faster when the temperature is hotter—the faster moving air molecules bump into each other more often.

7. Air is made of different molecules.
vsound = 343 m/s
Air is made of different molecules.
Sound travels faster when the temperature is hotter—the faster moving air molecules bump into each other more often.

8. “Compressions” and “Rarefactions”
Imagine a tuning fork vibrating.
As the fork moves in the forward direction, it begins to push the surrounding air molecules to the right.
This causes the air molecules to the right of the fork to experience a “compression,” or high pressure.
As the vibrating fork moves in the reverse direction (left), it lowers the pressure of the air immediately to its right, causing their to be a “rarefaction,” or low pressure.
A sound wave is a longitudinal wave disturbance, which is made of a series of compressions and rarefactions.

9. Sound is a Longitudinal Wave Disturbance
Tuning Fork GIF:
Vibrating String GIF:
Wave Simulator:

10. Sound Waves are Pressure Waves
A sound wave is really a wave of air pressure changes.
Any detector of sound waves—like your ear or a microphone—must be able to detect air pressure fluctuations. After all, that’s what sound is!

11. Sound Waves are Pressure Waves
A sound wave is really a wave of air pressure changes.
Any detector of sound waves—like your ear or a microphone—must be able to detect air pressure fluctuations. After all, that’s what sound is!

12. The Sound Barrier
If a fast-moving object moves faster than the speed of a sound wave, pressure will build up creating a barrier! Breaking past this barrier creates a sonic boom!

13. https://youtu.be/CeTiOuite5I

14. Frequency and Pitch
Our eardrums can detect the pressure fluctuations of a sound wave (air pressure fluctuations) and we perceive the frequency as a certain pitch, or relative highness or lowness of the sound.
The human ear is capable of detecting sound waves with a wide range of frequencies—from 20 Hz to 20,000 Hz!
Any frequency below 20 Hz is called “infrasound” and any frequency above 20,000 Hz is called “ultrasound.”
Some animals can detect even higher frequencies— dogs (45,000 Hz), cats (85,000 Hz), dolphins (200,000 Hz).

15. Microphones and Pressure Waves