Section 1 The Nature of Sound Chapter 12 Sound Section 1 The Nature of Sound

What Causes Sound? Sounds are all different but they are all produced by an object that vibrates. How does the sound get to your ear? -something vibrates, it collides with nearby molecules in the air, energy is transferred and it goes on and on in a compressional wave. This process of collisions and energy transfer forms a sound wave. Eventually the wave reaches your ear. Compressional waves are made up of compressions and rarefactions which push air molecules together and then spread them apart.

Moving Through Mediums Sound waves can travel through any type of medium: solid, liquid, or gas. However, sound waves can not travel through empty space. 1. Sound wave’s speed depends on the substance of the medium and whether the medium is a solid, liquid or gas. 2. Sound travels faster in liquids and solids because the molecules are closer together so they can transmit energy to one another more rapidly. The speed of sound does not depend on the loudness of the sound…loud sounds travel through a medium at the same speed as soft sounds. As a medium’s temperature increases, its molecules move faster and it conducts sound waves faster.

Human Hearing- Four Stages 1. The outer ear gathers sound waves passing them through the ear canal to a tough membrane called the eardrum. 2. The vibrating eardrum passes the sound to three tiny bones in the middle ear called the hammer, the anvil, and the stirrup which amplify the sound. 3. The stirrup vibrates and transfers the sound to a membrane in the oval window, then on to the inner ear’ s cochlea, a spiral shaped structure that contains hair cells. 4. As the hair cells in the cochlea vibrate, nerve impulses are sent through the auditory nerve to the brain.

Human Ear Hammer Anvil Stirrup

Section 2 Properties of Sound Quieter sound waves don’t carry as much energy as louder sound waves do. Remember: the amount of energy a wave carries corresponds to its amplitude. For a compressional wave, amplitude is related to the density of the particles in the compressions and rarefactions.

Intensity Intensity is the amount of energy that flows through a certain area in a specific amount of time. Loudness is the human perception of sound intensity. Each unit on a scale that measures sound intensity is a decibel. The faintest sound a human can hear is 0 dB. Normal human voices are 60 dB. Sounds above 120 dB may cause pain and permanent hearing loss.

Pitch Pitch is how low or high a sound seems to be. Pitch is related to the frequency of the sound waves. 1. Frequency is the number of compressions or rarefactions of a sound wave that pass per second; human ears can hear frequencies from about 20-20,000 Hz. 2. Ultrasonic waves are sound frequencies over 20,000 Hz that have medical and scientific uses. 3. Infrasonic or subsonic waves with frequencies below 20 Hz usually can’t be heard but may feel like a rumble. Doppler effect- change in pitch or wave frequency due to a moving wave source –either the source of the wave or the observer can be moving. Example: race cars moving by

Section 3 Music Music is sounds that are deliberately used in a regular pattern. 1. Natural frequency is the frequency at which the material vibrates. 2. Resonance is the ability of a medium to vibrate by absorbing energy at its own natural frequency. Sound quality is the differences among sounds of the same pitch and loudness. 1. Fundamental frequency is the main tone played and heard. 2. Overtone is the vibration with a frequency that is multiple of the fundamental frequency.

Musical Instruments Musical instruments are devices used to make musical sounds. 1. Strings are instruments in which sound is produced by plucking, striking, or drawing a bow across tightly stretched strings.

2. Brass and woodwinds = air vibration in a resonator, or hollow chamber that amplifies sound with the pitch determined by the length of the vibration tube of air.

3. Percussion instruments produce sound by being struck, shaken, rubbed, or brushed. Beats = a pulsing vibration in loudness

Section 4 Using Sound Sound is used for entertainment, warning signals, and information 1. Acoustics = the study of sound, which can prevent excessive reverberation and create good listening environments 2. Echolocation = process of locating objects by sending out sounds and interpreting the waves reflected back. 3. Sonar = a system that uses the reflection of underwater sound waves to locate objects 4. Ultrasound waves are used in medicine to diagnose,monitor, and treat many conditions Can produce images of internal structures for detection of medical problems Can treat certain medical problems such as kidney stones or gallstones