1. Properties of sound Sound is a longitudinal wave
Longitudinal waves travel at different speeds depending on the medium 25oC 346m/s, water 1490 m/s)
Denser the medium, the faster it travels, energy can transfer faster through molecules closer together.
Loudness of a sound
depends on intensity (the amplitude of the wave. Higher amplitude … louder sound)
Measured in deciBels (dB), talking is about 50 dB over 120 dB is painful.

2. Loudness/intensity

3. Properties of sound
Pitch (high or low) is directly related to frequency. Higher frequency = higher pitch
(Also related to wavelength, indirectly. Bigger wavelength = lower pitch)
Humans hear between 20 Hz and 20,000 Hz. Below that range is infrasound, above is ultrasound.

4. Musical Instruments Rely on standing waves to make sound
Only certain wavelengths are made by instruments, depending on the size of the instrument
Fundamental frequency: the lowest
frequency standing wave made by the instrument.

5. Stringed Instruments
The wavelength of the fundamental frequency is twice the length of string.
Changing the size of the string changes the wavelength and the frequency.
Changing the tension on the string changes the medium (density) and the wave speed

6. Wind/Brass Instruments
Change size of wave by opening closing holes, changes size of tube that standing wave is made in.
In a tube open at both ends, you get ½ the wavelength, so multiply by 2 to find the wavelength for the fundamental frequency
In a tube closed at one end, you get ¼ the wavelength, so multiply by 4 to find the wavelength for the fundamental frequency

7. Musical Instruments Strings make ½ wave, so mult. by 2.
Open tubes make ½ wave so mult. by 2
Closed tubes make ¼ wave so mult. by 4.

8. Resonance and Harmonics
Vibrations can cause other parts of the instrument and other objects to vibrate … called resonance.
The other standing waves created are called harmonics.
That’s why everyone’s voice sounds different and why instruments sound different when they play the same note. The have the same fundamental frequency (note), but different harmonics because of resonance
Waves interfere, called beats

9. How we hear
Outer ear focuses waves, passes them to ear drum (middle ear) which passes them to three bones (hammer, anvil, stirrup) to the cochlea (inner ear) which resonates at certain frequencies.
Hair cells pick that up and transmit to brain.

10. Ultrasound and Sonar
Use speed of sound in medium and time to figure out how far away something is (e.g. bottom of ocean floor)
Ultrasound...frequencies beyond our hearing used in medicine (babies).