SOUND WAVES(8.5)

Properties of Sound Waves Are longitudinal waves Require a medium to travel through The type of medium influences the speed

of the sound wave Sound travels faster at higher

temperatures Sound waves can also be affected by

humidity and air pressure

Comparison for Speed of Sound in Different Mediums

Table taken from pg. 395 of Nelson Physics 11

Additional values can be found at:

http://www.physicsclassroom.com/class/sound/Lesson-2/The-Speed-of-Sound

Medium Speed of Sound (m/s)

Air (20oC) 344Air (0oC) 331

Air (- 20oC) 319Glass

(Pyrex)5170

Steel 5000Water 1496Wood

(maple)4110

Experimental Formula for the Speed of Sound in Air

Where v is the speed of sound in air in m/s

T is the air temperature in degrees Celsius

(Formula based on analysing speed-temperature data)

Sound Intensity Humans describe how loud a sound is by

its sound intensity.

Sound intensity is the amount of sound energy being transferred per unit area (Units: )

The larger the amplitude of a sound wave the more energy it is transferring and the louder the sound you will hear.

Sound Intensity Sound intensity levels is often described

in decibels (dB).

Decibels are a measure of sound level and uses a logarithmic scale to show the different in sound intensity.

Loudness levels are dependent on the distance from the source of the sound.

Audible Sound Waves

Type of Sound Wave

Frequency Example

Infrasonic Waves

< 20 Hz Earthquakes

Audible Sound Waves

20 Hz – 20 kHz Dog bark, whisper, etc.

Ultrasonic Waves

> 20 kHz Ultrasounds, Ultrasonic ranging

unit

Loudness and DistanceDistance

(m)Sound Level

(dB)

1 12010 10050 86

100 80200 74500 66

1000 602000 545000 46

10000 40

Further away from an object the quieter the sound becomes.

This is because the amount of energy carried is the same but the area the sound travels is greater. Thus decreasing the sound intensity.

Table taken from pg. 396 of Nelson Physics 11

Sound SafetyContinuo

us dBPermissible Exposure

Time85 8 h88 4 h91 2 h94 1 h97 30 min

100 15 min103 7.5 min106 3.75 min109 1.88 min112 0.94 min115 0.47 min

Hearing damage can occur when exposed to loud sounds for extended periods of time.

Exposure time depends on sound intensity.

Important to wear hearing protection when exposed to loud noises

Table taken from pg. 396 of Nelson Physics 11

Mach Number Mach number is the ratio of the airspeed of an object to the local speed of sound The local speed of sound may vary due to surrounding air temperatures Described by Austrian physicist Ernst Mach Mach 1 = speed of sound

Experiment to Measure the Speed of Sound in Air

Reverences http://

www.physicsclassroom.com/class/sound/Lesson-2/The-Speed-of-Sound

https://www.youtube.com/watch?v=NPPgQcFUrXk

https://www.youtube.com/watch?v=RRFV_gJQbB4

Nelson Physics 11