Sound Sound Waves

The Production of Sound Waves Sound waves are caused by vibrations –The vibrating object has regions of air with relatively high density and low density around it High density areas – compressions Low density areas – rarefactions Sound waves are longitudinal waves –They have compacted areas (compressions) and expanded areas (rarefactions)

The Production of Sound Waves

Characteristics of Sound Waves Humans can hear in a limited frequency range – between 20 and 20,000Hz –Audible sound waves Infrasound – any sound consisting of waves with frequencies lower than 20Hz Ultrasound – any sound consisting of waves with frequencies higher than 20,000Hz

Characteristics of Sound Waves Pitch – the perceived highness or lowness of a sound, depending on the frequency of sound waves Faster vibrations lead to higher pitch Higher frequency equals higher pitch

Characteristics of Sound Waves Ultrasound is used in sonar systems for boats and bats –Can produce an image Sonar – a system that uses reflected sound waves to determine the distance to and location of objects –Uses the formula distance = speed * time d=vt Ultrasound is also used in medicine –Sonograms to look inside a body to view internal organs –Don’t harm living cells like X-rays

Characteristics of Sound Waves Speed of sound depends on the medium Sound travels fastest through solids Sound travels slowly through gases Sound travels faster in hot temperatures than in cold temperatures Difference is due to ease of particle collisions in solids at high temperatures Certain solids slow down sound waves –Rubber

Characteristics of Sound Waves

Sound waves propagate (spread) in all directions, three-dimensionally, from the source of the vibrations –Centers of compression surrounding the source are called wave fronts –Radial lines perpendicular to the wave fronts are called rays Indicate direction of wave motion At large distances, spherical wave fronts appear to be located on a single plane –Plane waves

Characteristics of Sound Waves

The Doppler Effect Frequencies change when the source of the wave is moving Doppler effect – a frequency shift that is the result of relative motion between the source of waves and an observer –Frequency and pitch increase when the source is closer Blue shift –Frequency and pitch decrease when the source is further away Red shift Present in all waves

The Doppler Effect