 Sound is a disturbance that travels through a MEDIUM as a LONGITUDINAL WAVE

 Begin with a VIBRATION  Create a COMPRESSION (pushing particles together)  Create a RAREFRACTION (spread out)

 Sound waves carry ENERGY through a MEDIUM  Each PARTICLE of the medium VIBRATES as the disturbance passes.  When the DISTURBANCE reaches your ear, you HEAR the sound.

WATER AIR WOOD

 The speed of sound depends on the TEMPERATURE, STIFFNESS, and DENSITY of the medium the sound travels through.

Speed of Sound in Air The data in the table show how the speed of sound in air changes with temperature. Plot temperature on the horizontal axis and speed on the vertical axis to create a line graph. The Nature of Sound

 Sound travels SLOWLY at LOWER temperatures. › Why? Particles of the medium move SLOWER at lower temperatures

 Sound travels faster through STIFFER mediums. › Why? Particles are COMPRESSED making it quicker to spread out again.

 The more dense the medium, the SLOWER the sound travels › Why? When the particles are closer together the energy SLOWS DOWN and does not pass very quickly.

 Pitch – How high or low the sound seems to a person.  Frequency – The number of waves passing a given point each second. › The pitch of the sound you hear depends on the frequency of the sound wave.

The table compares the range of frequencies that humans and various animals can hear. Frequency is measured in hertz (Hz) 1 Hz = 1 vibration per second. Low frequency = low pitch and less vibrations High frequency = high pitch and more vibrations.

 Loudness – the loudness of a sound depends on the energy and intensity of the sound wave. › Energy – Causes distance of amplitude to increase therefore volume increases › Intensity – amount of energy sound carries through a unit area.  Closer you are the more intense the sound

Measuring Loudness The table compares the loudness of some familiar sounds. Measuring loudness Decibel (dB) – based on the intensity of the sound 0 dB – you can barely hear 10 dB – is 10 times more intense then a 0 dB

 The change in frequency of a wave as its source moves in relation to an observer is call the DOPPLER EFFECT. › This occurs because of the motion of the source causes the waves to either get closer together or spread out.

The Doppler Effect As the fire truck speeds by, observers hear a change in the pitch of the siren.

 The Nature of Sound › #6 and #8 are TRUE  Properties of Sound › #6 and #9 are TRUE   Username = student id  Password = first and last initial then student id  HS123456