1. Sound & Light

2. Production of Sound Waves
Sound Waves are produced when something vibrates.
This vibration causes the medium (like air and water) around it to vibrate
These vibrations are longitudinal waves which we can hear.
Compressions: areas of high pressure and high density of air molecules
Rarefactions: areas of low pressure and low density of air molecules

3. Sound frequencies Frequency: the number of cycles per second.
Pitch: a measure of how high or low a sound is perceived to be, depending on the frequency. (directly related)
Audible sound waves: 20 Hz < f < 20,000 Hz (depending on age and experiences with loud noises)
Infrasonic Waves: f < 20 Hz
Ultrasonic Waves: f > 20,000 Hz
Dogs can hear ultrasonic waves!

4. Speed of sound waves
Depend on the medium substance and temperature. (how quickly can one particles transfer its motion to another particle)
Substance
Can travel through solids, liquids, and gases.
Sound generally travels fastest through solids because the particles are closer together.
Temperature
At high temperatures, particles collide more frequently, so sound waves can travel faster than a lower temperatures. (most noticeable for gases) d

5. Speed of Sound in Various Media
Medium
v (m/s)
Gases
Air (0°C)
331
Air (25°C)
346
Air (100°C)
366
Helium (0°C)
972
Hydrogen (0°C)
1290
Oxygen (0°C)
317
Liquids at 25°C
Methyl alcohol
1140
Sea water
1530
Water
1490
Solids
Aluminum
5100
Copper
3560
Iron
5130
Lead
1320
Vulcanized Rubber 54
𝒗=𝒇λ
Speed of sound in air at STP: 331 m/s
Standard Temperature: 0°C
Standard Pressure: 1 atm

6. Waves travel in all directions.

7. The Doppler Effect
An observed change in frequency when there is relative motion between the source of waves and an observer.