1. Sound Waves

2. What causes sound?
Sound is a longitudinal wave caused by vibrations of a medium.
Humans perceive different frequencies of sound waves as different pitches.
Humans can hear between 20hertz and 20,000hertz.

3. Conduction of Sound
The closer molecules are together, the better sound will be conducted.
Gasses conduct sound poorly, liquids are better and solids are best.

4. The Speed of Sound The speed of sound depends on
Temperature
Humidity
Wind conditions
At normal room conditions, sound travels at 340meters per second

5. Reflection of sound An echo is a reflected sound wave.
When a sound wave hits a wall, the angle it bounces off the wall is the same angle that it hits the wall.

6. Refraction of Sound Refraction is the bending of a sound wave.
When a sound passes through different temperatures in the same medium, the sound bends.
Sound bends towards the cold air.

7. Uses of Refraction of Sound
Submarines can hide in thermal gradients
Ultrasounds are used to diagnose medical conditions
Animals use ultrasound refraction to track prey.

8. Forced Vibration
A vibrating object held can cause another object to begin vibrating at the same frequency
Soundboards on stringed instruments
Tuning fork amplication

9. Natural Frequency
The set of frequencies that an object vibrates at when struck.
Most objects have a natural frequency.

10. Resonance
When a forced vibration matches the natural frequency of an object, the amplitude of the motion increases.
Swings
Radios
Bridges

11. Tacoma Narrows Bridge Collapse Breaking Glass by Voice