Sound

Production of Sound Waves Sound waves are Longitudinal Longitudinal means that the particles in the medium vibrate how compared to the wave motion? Parallel Perpendicular Circular

Compression/Rarefaction

Characteristics of Sound Waves Audible Range: Range of sound the average human can hear. Low Frequency: 20 Hz High Frequency: 20,000 Hz

What is the range of sound called that falls below the frequency of 20 Hz? non-sonic infrasonic unsonic Antisonic

Infrasonic is the term used for a sound wave that falls below the 20Hz frequency. Humpback whales communicate on infrasonic frequencies. The term that describes sound waves above the 20,000 Hz frequency is called ultrasonic. Dogs can hear ultrasonic frequencies. This is why a good dog whistle cannot be heard by humans.

If the speed of sound is 343 m/s, what is the wavelength of an ultrasonic wave with a frequency of 35,000 Hz? .0098 0.01

Frequency determines the pitch of the sound Frequency determines the pitch of the sound. Whether the sound is a high or low pitch. Ultrasonic waves produce ultrasonic images.

Speed of Sound Depends on Medium Sound travels fastest through medium which are more dense. Why? Sound is the vibration of particles in a substance. The closer the particles, the faster the transfer of energy. Iron: 5130 m/s Water: 1490 m/s Air: 331 m/s @ 0° C

Why would the temperature of air effect the speed of sound in air? because hot air rises. because the temperature adds energy to the wave. because the particles in the air move faster.

In Fact….. The speed of sound in air increases by .6 m/s every °C the air temperature goes up. So at room temperature, 20 °C, the speed of sound in that room is 343 m/s.

The temperature on a hot sunny day is around 30° C, what is the speed of sound in m/s? 349 0.1

Sound waves propagate in 3 dimensions. Spherical wave fronts that are large distances away from the source appear to be plane waves.

The Doppler Effect Relative motion creates an Apparent change in frequency.

The Doppler Equation Vdetector: Positive if listener is moving toward source Vdetector: Negative if listener is moving away from source Vsource: Negative if source is moving toward listener Vsource: Positive if source is moving away from listener

A siren produces a frequency of 1500Hz A siren produces a frequency of 1500Hz. A runner who is passing the siren at 25 m/s hears the siren. What frequency is heard when the runner is going toward the siren? (Use 343 m/s for Vsound) 1390 Hz 1398 Hz 1617 Hz 1609 Hz

Loudness (Sound Intensity) The intensity or loudness of a sound is perceived by a person’s sense of hearing. Each person perceives sound differently. The intensity scale numerically determines the “strength” of the sound.

Intensity Scale Units: Watts/m2 2000 Watt speaker 1 meter away = 159.2 W/m2

A speaker has a intensity of. 50 W/m2 at a distance of 6 meters away A speaker has a intensity of .50 W/m2 at a distance of 6 meters away. What is the power output of the speaker? 226.2 0.5

Examples from the Intensity Scale

Decibel vs. Intensity Decibel scale is a Relative Loudness scale. It is based off of Created by A. G. Bell

Decibels For every power of 10 increase on the sound intensity scale, the decibels increase by 10. Scale starts at 0dB = 10-12 W/m2

Examples Decibel Scale

Decibels As stated earlier, decibels measure the relative loudness of sound. For every 10 dB, the sound is 2 times as loud. Therefore the difference between 0 dB and 120 dB is 4096 x louder.

Decibel If we have an object that is 20 dB and want to make a 50 dB sound, how many more objects do we need? Rule: for every 10 dB added, we increase the # of objects by a power of 10.

Decibel So for our last example we went from 20 dB to 50 dB which is a difference of 30 dB. 30 dB is 3 sets of 10 Therefore for every set of 10 we increase by a power of 10 1 = 20 dB, then 1000 = 50dB

Decibel What is we want to double the number of objects? Rule: if the number of objects are doubled, then the dB increase by 3. Example: if there are 200 goats that make 70 dB, then 400 goats make 73 dB.

IF one horn produces 50 dB how much louder is it if it produces 80 dB? 2 4 6 8

If there are 30 ants making a noise of 20 dB, how many ants would make a 60dB noise? 300000 30000 3000 300

40 bells make 70 dB. How many Bells are needed to make 96 dB? 16000 0.0