Lesson 11 of 13
The big picture
Show on a big screen| Idea | In short |
|---|---|
| Something has to shake | Stop the vibration and the sound stops |
| A medium | Usually fastest in solids, slowest in gases, none in a vacuum |
| What moves | The wave travels. The pieces shake in place |
| Loudness | Bigger amplitude, louder sound, more energy |
| Pitch | Higher frequency, higher pitch. f × T = 1. |
| What we hear | People hear 20 Hz to 20 000 Hz. Below is infrasound. Above is ultrasound. |
| Echo | A gap of 0.1 s or more. Wall = half the trip |
| Sonar | Depth = speed × time ÷ 2 |
| Wavelength | Speed = wavelength × frequency, or v = λ × ν. In one medium at one temperature, a higher frequency gives a shorter wavelength. |
A shake makes a wave. A medium carries the wave. Amplitude sets the loudness. Frequency sets the pitch.
Now open Chapter 10, Sound Waves: Characteristics and Applications. You met the main ideas here first.