1. Sound Chapter 12.1

2. Properties of Sound  Sound waves are caused by vibrations and carry energy through a medium.  The speed of sound depends on the medium  Table 12-1 shows the variations of sound speed in mediums such as water, copper, and rubber  Sound waves travel faster through liquids and solids than through gases.

3. Properties of Sound  The loudness of a sound depends on the energy contained in the sound waves and your distance from the sound source.  Relative intensity of sounds is found by comparing the intensity of a sound with the intensity of the quietest sound a person can hear.  This is measured in units called decibels, dB.

4. Properties of Sound  The quietest sound a human can hear is 0dB  A sound at 120 dB is the threshold of pain and can permanently damage your ears or even cause deafness.  Pitch – the perceived highness or lowness of a sound, depending on the frequency of sound waves.  Musicians use pitch to describe how high or low a note sounds.

5. Properties of Sound  Infrasound – any sound consisting of waves with frequencies lower than 20 Hz  Ultrasound – any sound consisting of waves with frequencies higher than 20,000 Hz.

6. Properties of Sound  Resonance – an effect in which the vibration of one object causes the vibration of another object at a natural frequency.  Ex. Guitar  The sound produced by the guitar will be loudest when the vibrations of the string cause the body of the guitar to vibrate.

7. Ultrasound and Sonar  Sonar – a system that uses reflected sound waves to determine the distance to, a location of, objects.  Ex. A ship measure the distance to the ocean floor  Ultrasound waves – sound waves with frequencies above 20,000 Hz.  Ex. Bats use ultrasound waves to navigate in flight and locate food