Introduction to Sound: Sound Waves

1
Introduction to SoundSound Waves

• Mr. V. Perez
• Grade 6 Science

2
What Is Sound?

• Sound is a form of energy
• Light waves travel in transverse waves (which
  travel up and down at 90? to the direction of the
  wave)
• Sound energy travels in the form of longitudinal
  waves
• In a longitudinal wave, the particles of air move
  back and forth in the same direction as the sound
  wave

3
Medium(s) for Sound

• How does sound travel?
• Sound travels through air, which is the medium
  for sound waves
• All sound waves need a medium to travel
• Sound waves can travel through solids, liquids,
  and gases
• Sound can travel through water, but it cannot
  travel in a vacuum like light can (because there
  are no particles in a vacuum)
• Sound waves are made up of compressions and
  rarefactions
• The top part of a sound wave is the compression
• The bottom part a sound wave is the rarefaction
• The amplitude is the distance from the
  equilibrium to the top of the wave (compression)
  OR the distance from the equilibrium to the
  bottom of the wave (rarefaction)

4
Compressions and Rarefactions

• How does the sound from a tuning fork travel?
• When the tines (prongs) of the tuning fork
  vibrate, they push on the air in front of it
• Air particles are squeezed together, which is
  called the compression
• When the tines move back the air molecules spread
  apart, which is called the rarefaction
• As the tuning fork keeps vibrating, compressions
  and rarefactions move away from the tuning fork
• They form a sound wave called a compressional wave

R C R C R C R C
R C R
5
Compressions and Rarefactions
C
C
C
C
R
R
R

• Sound waves are called compressional waves
  because the compressions (and rarefactions)
  travel through the air to make a wave

6
Parts of a Sound Wave
__
Vibration of Guitar String

• Sound waves can be measured from
• One compression to the the next compression
• One rarefaction to the next rarefaction
• One compression (180) and one rarefaction (180)
  Together they add up to 360 OR one sound wave