Presentation on theme: "Sound. Sound Waves Sound waves are longitudinal waves. The source of a sound wave is a vibrating object. Only certain wavelengths of longitudinal."— Presentation transcript:
Sound Waves Sound waves are longitudinal waves. The source of a sound wave is a vibrating object. Only certain wavelengths of longitudinal waves in the air can be detected as sound.
Sound Waves Sound waves require matter in order to propagate. They cannot travel in a vacuum The speed of sound is different in different materials. The speed of sound is also somewhat dependent on temperature.
Speed of Sound Air (room temp) – 343 m/s Air (0° C) – 331 m/s Helium – 1005 m/s Water – 1440 m/s Steel – about 5000 m/s Concrete – about 3000 m/s
Loudness Loudness is related to intensity. Loudness itself is not a measurable physical quantity. It depends on the listener. Intensity is measurable, however.
Loudness Sound intensity levels are usually given on a logarithmic scale. The unit on this scale is the decibel (dB) β = 10 log (I/I ₀ ) β = sound level (in dB) I = sound intensity I ₀ = base sound level
Loudness The base sound level used (I ₀ ) is usually what is know as the “threshold of hearing” This is the minimum intensity that is audible to a good ear. 1.0 x 10ֿ¹² W/m²
Sound Intensities Threshold of hearing – 0 dB Whisper – 20 dB Talk, at 50 cm – 65 dB Busy street traffic – 70 dB Loud rock concert – 120 dB Jet plane at 30 m – 140 dB
Pitch Pitch is related to frequency of a sound wave. A high pitch corresponds to a high frequency. The audible range is the range of frequencies that a normal person can hear.
Pitch Frequencies between 20 Hz and 20,000 Hz are audible. The threshold of hearing varies for different frequencies. It is easiest to hear sounds between 2000 and 5000 Hz.
Pitch Frequencies too high to hear are ultrasonic. Some animals can perceive sounds up to 100,000 Hz (bats) Frequencies too low to hear are infrasonic.