Physical Science Chapter 11: Sound

Sound Waves Sound waves are a type of compressional wave which require a medium to travel.

The study of sound is called acoustics.

• Sound waves travel at about 750 mi/hr. This speed is effected slightly by the type of medium, temperature of medium (directly proportional), and elevation.

Ok, quick review:

• Frequency is a property of a wave, not a part of one.

• Frequency is the number of waves which pass a given point in 1 second.

• Hertz (Hz) is the SI unit for frequency.

1 Hz = 1 wave passing a given point in

1 second

Compressional WavesCompressional Waves A compressional wave vibrates in the

direction that the wave is travelling. Examples: slinky, sound waves

• The 2 main parts of a compressional wave are:

A. Compression- area of higher density

within the wave

B. Rarefaction- area of lower density

within the wave pg. 464

• When an object such as a jet travels at a speed greater than 750 mi/hr it is said to be supersonic.

• What happens when an object travels at supersonic speeds?

Pitch• Pitch is how high or how low a sound is to

the human ear.

This is determined by the sound frequency, which is directly proportional to the sounds pitch.

pitch frequency

pitch frequency

Humans can only hear sounds which are within a certain range. For the average person this range is from approximately 20 Hz to 20,000 Hz (vibrations per second).

• Frequencies above 20,000 Hz, and beyond the normal range of human hearing are called ultrasonic.

• Very high frequency sound waves can be used in the medical field.

• Ultrasonic waves can be used to break up kidney stones and gall stones.

• Ultrasound imaging uses the reflections produced by ultrasonic sound waves to produce images from inside the body.

• What advantages do you think ultrasonic sound waves would have over x-rays or MRI’s?

• Sounds below the normal range of human hearing (20 Hz) are called subsonic, or infrasonic.

Music is a combination of specific sounds used in a regular pattern.

Musical notes are produced by sound vibrations at a certain frequency.

However, even though certain notes correspond to certain frequencies, different people may perceive these notes differently.

• Natural frequencies are the frequencies at which an object or material will vibrate when it is disturbed.

• The right frequency combined with enough energy (loudness) in a sound wave could cause a wine glass to vibrate at it’s natural frequency (resonance) and eventually break due to constructive interference.

• Other examples of resonance

LoudnessLoudness is human perception of sound intensity (the amount of energy in the wave), and is measured on the decibel scale (dB).

Loudness is subjective to the individual. However, the decibel scale still assigns numeric values to different levels of loudness.

• What is the lowest value on the decibel scale, and what does it represent? and the highest?

• Strong shock waves could produce a condition called lethal over-pressure shock. This is caused by a large increase in air-pressure (100 p.s.i.+) and can actually result in death. Large explosions in the area of 200 dB’s or more can produce such a condition.

Doppler Effect

• The Doppler effect is a change in wave frequency due to a moving wave source.

• The frequency is higher in the direction that the wave source is moving and lower in the opposite direction.

A bug swimming in a pool of water produces waves which exhibit the doppler effect.

• Other examples of the Doppler effect include radar guns, sounds produced by a racecar or an ambulance, and Doppler radar.

Doppler radar uses radio waves to detect winds, clouds, and precipitation in order to identify and forecast weather.

• Doppler radar can identify a tornado and issue a warning without having an actual eye-witness to the event.

• Sounds can also bounce off of objects or surfaces.

• When a sound wave bounces off and returns to the wave source, it is called an echo.

• When an area produces multiple echoes, this is called reverberation, or reverb.

• Echolocation is the process of locating and identifying objects by interpreting sound waves which are reflected back.

• Bats will used high pitched squeaks, echolocation, and the Doppler effect to locate food.

• Echolocation can also be used under water. It is called SONAR when it is used underwater.

SOund

Navigation

And

Ranging

• Humans and animals alike will use SONAR to detect and identify underwater objects and structures.

• Fish finders and depth finders are common uses for SONAR.

White Noise

• White noise is a combination of sounds at different audible frequencies, used to mask out annoying background noises.

• Say you're listening to 2 people talking at the same time. You would be able to pick out one of the 2 voices.

If 3 were talking, their speech would be more inter-mixed, but you could still probably pick out 1 person's voice.

How about if 50 were talking at the same time and same volume, could you pick out 1 individual voice?

• That's kind of how white noise works.

It has a combination of different sounds at different frequencies within the range of 20-20,000 Hz. Any background sounds will blend into this, and be masked over. The resulting sound is similar to static you may hear from your t.v.

• Think of it like a Where’s Waldo cartoon. Waldo is in there somewhere, it’s just hard to pick him out of the crowd. White noise does that to the annoying background noises that you’d prefer not to be distracted by.

• So what exactly does white noise sound like?

• Could you say that white noise blocks out background noises?

•Why do you think it's called white noise?

• What are some places where white noise might be used?

• A bored scientist decided to see what would happen if he let a bat loose in a sound proof chamber like the one pictured. He also let a few moths loose in the chamber as well, for food. Describe how the bat most likely behaved inside the chamber.

Jared loads luggage into planes at KCI. The headphones he was issued for hearing protection from the noise were very uncomfortable, so he bought his own pair of “noise canceling” Bose headphones. Will these work about the same, better, or worse than his original headphones? Explain.

• James is going to the Gulf Coast for vacation to do some fishing. He takes his boat and his fish finder. Will the fish finder which he normally uses in fresh water work well in salt water? Explain your answer.

• Is it possible for a sound which is not audible to our ears to cause hearing damage? Explain.

• Fish finders use frequencies in the 50-200 kHz range. Why do you think this is so? (give 2 reasons)

• What sound wave property does the intensity of the wave determine, pitch or loudness? Is this always true? Explain.

• Why do you think radio waves are used for radar (through the air), but not for SONAR?

• Meredith heard a noise in her backyard. So she went out back out shined a flashlight around, and found a raccoon messing around. So you could say that she used Lidar. What?!?

• As the teacher was writing on the chalk board, the chalk suddenly screeched and caused several students to jump. Why did they respond this way?

• Todd noticed that when he had a head cold and was all stopped up, every sound that he heard sounded muffled. Why do you think this happened?

• When Angela, Pam, and Kelly were swinging at the park, Kelly was able to go much higher than the other two. “What’s you’re secret for swinging so high”, asked Pam. “Resonance my friend, resonance”. What did Kelly mean?

• The B-2 stealth bomber is designed to make it nearly invisible to most radar systems. What are some ways that an aircraft such as the stealth could decrease it’s visibility to radar?