Chapter 10 Section 2: SOUND

REMINDER from last week Waves can be classified in two ways: The way they travel: - compressional (energy and particles move parallel) - transverse (energy and particles move at right angles) OR 2) The medium(s) they travel through: - mechanical (matter only) - electromagnetic (matter or empty space)

A. Sound waves are produced by vibrating objects A. Sound waves are produced by vibrating objects. They are compressional waves. 1. Ex: A vibrating drum head produces a compression as it moves upward and a rarefaction as it moves downward.

A. 2. The energy carried by a sound wave is transferred by the collisions between the particles in the material the wave is traveling in. 3. Sound waves cannot travel through empty space because they need particles to transport energy. This makes them mechanical waves.

B. The speed of sound depends on the matter through which it travels. 1. Sound waves usually travel faster in solids and liquids than in gases. 2. The speed of sound through a material increased as the temperature increases.

C. The amount of energy that a wave carries past an area each second is the intensity of the sound. The intensity of sound waves is measured in units of decibels (dB). 2. The intensity of sound decreases with distance from the source.

3. The softest sound a person can hear has an intensity of 0 dB. 4. Sound with intensities of about 120 dB or higher are painful to people. 5. Loudness is the human perception of the intensity of sound. 6. For every 10 dB in intensity a sound increases, humans perceive that the loudness doubles.

Practice Problems If the intensity of a sound increased 20 dB, how many times louder would it seem? 10dB = 2x louder so 20 dB = 4x louder 2) If a sound was heard 8 times louder, how many dB in intensity must it have increased? 2x louder = 10 dB so 8x louder = 30 dB

D. Pitch is the human perception of the frequency of sound. 1. Sounds with low frequencies have a low pitch, sounds with high frequencies have a high pitch. 2. Humans can hear sounds in the range from 20 Hz to 20,000 Hz.

E. The human ear can be divided into three parts. 1. The outer ear (the part of the ear you can see and the ear canal) is the sound collector. 2. The middle ear ( the ear drum and 3 bones – the hammer, anvil, and stirrup) is the sound amplifier. 3. The inner ear (the fluid-filled, hair lined cochlea) is the sound interpreter.

Ear canal

F. Echoes are sounds that reflect off of surfaces. 1. Repeated echoes are called reverberations. 2. Reflected sounds can be used to locate or identify objects. a. Echolocation is used by some animals to locate prey and find their way. b. Ultrasonic (very high frequency) waves commonly known as ultrasounds, are used in medicine to look at structures inside the body.