Chapter 16 Sounds

Chapter 16 Sounds

1. Causes?

   • Sound travels through medium
     • Hear sound made by engine of aeroplane as air surrounds
     • Can't Hear sound by astronauts in space as no matter surround space shuttle
     • Ringing of bell goes silent if air absent as vibrations of ringing bell not passed to surrounding molecules
   • Sound travel in matter
   • Vibrations of matter

2. How sound travels?

   • Moves right, surrounding molecules pushed closer tgt. Molecules move & collide with other molecules. Moves left, creates area with few molecules. (Side to side motion cause molecules move side to side in regular pattern which helps carry sound energy away)
   • Sound produced shown as ripples moving away frm source. Each ripple = where molecules bunch up
   • Different medias = different speed (When molecules at one end start to vibrate, energy transferred to neighbouring molecules...)
     • Solid: Fastest as molecules packed very closely. 5000-6000m//s
     • Liquid: (Scuba divers tap metal pointer on metallic air tanks to draw diver's attention) Less rapidly as molecules not as packed closely as solid. 1500m/s
     • Gas: Slowest as molecules far apart from one another. 330m/s

3. How we hear?

   • Hearing aids improve sense of hearing. Helps ppl with hearing loss. Vibrating molecules cause structures within ears to vibrate. Vibrations pass sound energy to ears. Brain translate vibrations into information. Hearing aid increases loudness of sounds by producing greater vibrations.
   • 1) external ear(cup-like flap) collects sounds
   • 2) ear canal(tube) channels sound to eardrum(flap of skin), vibrates to frequency of sound
   • 3) Vibrations transferred by 3 bones(hammer, anvil & stirrup) to inner ear
   • 4) vibrations transferred to cochlea(shell-shaped chamber), it vibrates to diferrent frequencies
   • 5) Ear nerves receive electrical signals then sends signals to brain which interprets sound

4. How sound varies

   • Pitch
     • Low pitch: Cow mooing + sounds made by bass guitar or large drum. Larger inturments
     • High pitch: Dentist's drill @ high speed + mouse squeaking. Smaller insturments
     • Frequency: No. of cycles per second made by vibrating source of sound. Unit: hertz(Hz)=1 cycle per second. Human Ear: 20Hz to 20000Hz
       • Higher frequency, higher pitch of sound produced
   • Loudness
     • Depends on how big vibrations in medium are. Greater vibrations(greater energy produced), louder sounds.

5. Sound + Society

   • Uses of sound
     • Warning of Danger
     • Entertainment
     • Communication
   • Sonar
     • Technique that uses sound to gather info. about environment. Reflected sounds(echoes)
     • 1)Ships emits sound that travels down to ocean floor. 2)Time interval for sound to go frm ship to ocean floor and back is measured. 3)Speed of sound= 2D/Time taken*Find D by dividing answer by 2.
   • Ultrasound + techynology
     • Ultrasound used in hospitals to observe internal body without need of operation. Eg Observe foetuses, detect cancers, observe tumours, monitor blood flow in veins, heart abnormalities and break up kidney stones top be passed out easily without operation
   • Noise
     • a collection of notes that is unpleasant and may be harmful. Eg Scratching chalk on blackboard, dishes breaking + Yowling cats at night
     • Range of noise pollution: Noise pollution is excessive noise that come from humans, animals or machines. Cause annoyance/health problems. Loudness is measured in decibels(dB). Sounds shld keep within acceptable limits as high sound levels have negative health consequences. Eg hearing impairment(burst eardrums)

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