Section 2: Properties of Sound Chapter 2: Sound Section 2: Properties of Sound

Discover Activity: How does amplitude affect Loudness pg. 42 1 volunteer is needed: rest of students take notes on this activity on the back of this packet. Volunteer, take the pink harp (toilet seat) and pull back one of the strings 1 cm to one side. This distance is the amplitude of vibration. Let it go. How far does the string move to the other side? Describe the sound you hear. Repeat Step 2 four more times. Each time, pull the string back a greater distance. Describe how the sound changes each time. How would you define the amplitude of the vibration? What effect did changing the amplitude have on the sound?

Loudness- describes your perception of the energy of a sound. -describes what you hear - the closer you are to sound the louder it is A. The loudness of a sound depends on two factors: the amount of energy it takes to make the sound and the distance from the source of the sound.

Energy of a Sound Source: 1. recall: the greater the amplitude of a wave, the more energy the wave has. 2. Therefore: the greater the energy used to make a sound, the louder the sound Ex: pulling the string back farther generates a louder sound Distance From a Sound Source: 1. Why does loudness increase the closer you are to a sound source?

2. The closer the sound wave is to its source, the more energy it has in a given area. a. The total energy of the wave stays the same whether it is close or far from the source 3. intensity- the amount of energy a sound wave carries per second through a unit area Insert transparency 020

D. Measuring Loudness- 1. decibel- the unit used to compare the loudness of different sounds Ex: soft music = 30-dB Ex: whisper = 20-dB

A. The pitch of a sound that you hear Pitch- of a sound is a description of how high or low the sound seems to a person. A. The pitch of a sound that you hear depends on the frequency of the sound wave. B. Pitch and Frequency- 1. high frequency = high pitch a. 50 Hz = 50 vibrations per second b. Most people hear sounds with frequencies b/n 20-20,000 Hz

3. infrasound- sounds with frequencies C. Changing Pitch- 2. Ultrasound - sound waves with frequencies above the normal human range of hearing 3. infrasound- sounds with frequencies below the human range of hearing C. Changing Pitch- 1. pitches are usually called notes 2. larynx- aka. the voice box part of the throat that contains the vocal cords

a. Air from the lungs is forced up the trachea past the vocal cords causing vibration 1. result = sound waves 2. vocal cords can vibrate more than 1,000 times per second 3. tight vocal cords = higher pitches 4. same applies to guitar string, tighter stings = higher frequency = higher pitch https://www.youtube.com/watch?v=74JzBgm9Mz4

The Doppler Effect: A. The Doppler Effect- is the change in frequency of a wave as its source moves in relation to an observer. Ex: Fire truck and siren: 1. sound stays the same for the firefighters in the truck 2. pitch of the siren drops as the truck passes an individual https://www.youtube.com/watch?v=z0EaoilzgGE

B. Causes of the Doppler Effect – 1. When a sound source moves, the frequency of the waves changes because the motion of the source adds to the motion of the waves. C. What Causes Shock Waves? 1. sound waves pile up as plane travels almost as fast as speed of sound. a. pile up of waves is the “sound barrier” b. A shock wave forms as the sound waves overlap. 1. shock wave releases a huge amount of energy heard as a sonic boom

https://www.youtube.com/watch?v=-d9A2oq1N38