Sound Waves
Unit 2 Lesson 1
Sound Waves
• ALL sounds are created by vibrations
(whether you can see the vibration or not.)
• ALL sound waves need a medium to travel.
– Quickest through solids because particles are closest together
• All sound waves are longitudinal waves.
– Particles of a medium vibrate in the same direction the wave
travels.
– Made of compressions and rarefactions
– After a wave passes through a medium, particles are in their
original position.
How do we hear?
1. Sounds enter the outer ear.
2. The compressions and rarefactions in the
sound wave vibrate the eardrum.
3. The vibrations pass into the inner ear.
4. The inner ear converts vibrations into
electrical signals.
5. The brain then interprets those electrical
signals as the sound you hear.
Damaging hearing
• Sounds over 120 decibels are painful to
human ears.
– Large compression waves cause vibrations that
damage the ear.
Pitch and Frequency
• Pitch & frequency: measured in high and low
• Pitch depends on the frequency and wavelength of a
sound wave.
• Pitch and frequency are not related to how loud or soft
a sound is.
• Frequency is measured in Hertz (Hz).
• One wavelength = distance from one crest to the next.
– A low-pitched sound has a low frequency and longer
wavelength.
– A high-pitched sound has a high frequency and a shorter
wavelength.
Loudness and Amplitude
• Loudness is a measure of how well a sound can be heard.
– Soft or Loud
– Measured in decibels(dB).
• Amplitude is related to how much energy a sound wave
carries.
– The maximum distance the particles travel
• The greater the amplitude, the louder the sound
** The more amplitude a sound wave has, the farther distance it
can travel.
Doppler Effect
• Doppler effect is a change in the observed
frequency of a wave when the source, the
observer, or both are moving.
– ** Doppler effect = change in frequency of the
sound wave.
1. Closer to the sound source = shorter wavelength,
therefore higher frequency and pitch.
2. Farther away= longer wavelength, therefore lower
frequency and pitch.
Doppler Effect