Sound

F 50-53

What Makes Sound?

• Sound is provided by making something move back and forth vibration

• Many of the vibrations are too fast for you to see but sometimes you can feel it (example: a bat hitting a ball)

Energy transfer

• If you pluck a guitar string you can see it moving back and forth; you provided the energy necessary for this vibration

• Vocal cords in your throat vibrate when air moves past them allowing you to speak

• Not all instruments rely on strings to make their sounds

Instrument Type of Vibration Example

Brass Vibrating Air Trumpet or Tuba

Woodwinds Vibrating ReedVibrating Wind

Oboe or Clarinet Flute or Piccolo

Percussion Vibrating Surface Drums or Piano

Strings Vibrating Strings Guitar or Violin

Sound waves

• Sound is a vibration that travels through matter (anything that takes up space)− When a string vibrates, it makes molecules of

gases in the air next to it vibrate,− the molecules squeeze together then spread

apart− these molecules make the molecules next to

them vibrate as well

− A vibration that spreads away from a vibrating object is as sound wave

− it carries the energy from the vibrating object outward in all directions (F51)

Sound Waves

• Compression the part of the sound wave where the molecules are crowded together

• Rarefaction the part of the sound wave where the molecules are spread apart

Compression

Rarefaction

What else can sound go through?

• You can hear sounds in the air; when sound waves reach your ear they make parts in the ear vibrate

• since air is a mixture of gases, you can conclude that sound travels through gases in the form of a sound wave

• Solids• You can tell that sounds travel through solids by

putting your ear onto a tabletop; if someone taps on the other end it is easier to hear with your head on the table rather than in the air

• If you want sound to travel through a thick solid or to be louder, you must apply more force

• Liquids• You can hear sound through liquids although it

may seem somewhat distorted