Interactions of Sound Waves Sound Quality Chapter 9 The Nature of Sound What Is Sound? Properties of Sound Interactions of Sound Waves Sound Quality Concept Mapping

What Is Sound?

1) All sounds are created by vibrations. a) A vibration is the complete back-and-forth motion of an object or material. Web site

2) Sound Waves are longitudinal waves that are caused by vibrations. source They travel in all directions away from their source.

3) There are no particles to vibrate in a vacuum (a place without air); so, no sound can be made in a vacuum (like outer space)

Quick Check You are the commander of a space station located about halfway between Earth and the moon. You are in the Command Center, and your chief of security tells you that sensors have just detected an explosion 61.054 km from the station. How long will it be before you hear the sound of the explosion?

Quick Review - don’t copy Sound and Media All sound waves require a medium (plural, media). medium a substance through which a wave can travel by vibrating particles in the material. Air is the most common medium of sound waves. Vacuums: There are no particles to vibrate in a vacuum. So, no sound can be made in a vacuum.

Properties of Sound

1) The speed of sound depends on the medium in which the sound is traveling. Don’t copy Sound travels quickly through air, but in general it travels even faster in liquids and even faster in solids (But not always)

3) How low or high a sound seems to be is the pitch. High frequency = high pitch Web site

Properties of Sound

Sounds that have too low a frequency are called infrasonic. 4) Sounds that have a frequency too high for people to hear are called ultrasonic. Sounds that have too low a frequency are called infrasonic. Ultrasonic Pestrepeller Sources of infrasound in nature include volcanoes, avalanches, earthquakes, elephants and storms.

5) The Doppler Effect is the apparent change in the frequency of a sound, caused by the motion of either the listener or the source of the sound. Applet

Doppler Effect and Sound Properties of Sound Doppler Effect and Sound

6) Loudness is a measure of how well a sound can be heard. 7) The larger the amplitude, the louder the sound. Click for web demo Loudness is measured in the unit decibels.

Quick visual – don’t copy “Seeing” Amplitude and Frequency A device called an oscilloscope can graph representations of sound waves, as shown below. Notice that the graphs look like transverse waves rather than longitudinal waves.

As frequency increases, does pitch get higher or lower? Quick Review – Don’t Copy – discussion only On an oscilloscope, does a wave with a larger amplitude indicate louder sound or higher pitch? As frequency increases, does pitch get higher or lower? What is the speed of sound dependent on? What do think happens when two sound waves interact with each other?

Interaction of sound waves Movie – Ben Underwood

1) Reflection is the bouncing back of a wave after it strikes a barrier. An echo is a reflected sound wave. The strength of a reflected sound wave depends on the reflecting surface. Sound waves reflect best off smooth, hard surfaces.

The images below explain why you are more likely to hear an echo in a gymnasium than you would in an auditorium.

Some cool info – don’t copy! Echolocation is the use of reflected sound waves to find objects. Animals, such as bats use echolocation to hunt food and find objects in their path. Animals that use echolocation can tell how far away something is based on how long it takes sound waves to echo back to their ears. Movie- Ben Underwood

More cool stuff – not to copy Echolocation Technology People use echoes to locate objects underwater by using sonar. Sonar is a type of electronic echolocation. Sonar can also help navigators on ships avoid icebergs and can help oceanographers map the ocean floor.

More cool stuff that shouldn’t be copied Ultrasonography is a medical procedure that uses echoes to “see” inside a patient’s body without doing surgery. Ultrasonography is used to examine kidneys, gallbladders, and other organs. It is also used to check the development of an unborn baby in a mother’s body.

2) Interference happens when two or more waves overlap 2) Interference happens when two or more waves overlap. Two types of interference are shown below.

Cool Stuff to not copy! Interference and the Sound Barrier As the source of a sound—such as a jet plane—gets close to the speed of sound, the sound waves in front of it combine by constructive interference. The result of this interference is a high-density compression called the sound barrier.

Nope – still not copying! When a jet reaches speeds faster than the speed of sound, the sound waves trail off behind the jet. At their outer edges, the sound waves combine by constructive interference to form a shock wave. A sonic boom is the sound you hear when a sound wave reaches the speed of sound.

Youtube, Sonic boom Time warp/You tube Flight – Sonic Boom/Youtube Interactions of Sound Waves Flight – Sonic Boom/Youtube Youtube, Sonic boom Time warp/You tube

3) A pattern of vibration that looks like a wave that is standing still is called a standing wave. Standing waves form because of interference. Where you see maximum amplitude, waves are interfering constructively. Where the wave seems to be standing still, waves are interfering destructively.

Sound Quality

1) The result of several pitches mixing together through interference is sound quality. (Don’t Copy) - Instruments sound different because each has a unique sound quality, as shown below.

Noise is any sound that is of a random mix of frequencies. The difference between a musical sound and noise is shown in the images below.

The Nature of Sound Concept Mapping Use the terms below to complete the Concept Mapping on the next slide. loudness oscilloscope frequency sound interference pitch medium

Chapter 21 The Nature of Sound

Chapter 21 The Nature of Sound

CRCT Preparation 1. During a laboratory investigation, Aaron used an oscilloscope to create graphs of sounds that he produced using tuning forks. Which of these four graphs represents the sound that has the lowest volume? A graph 1 B graph 2 C graph 3 D graph 4

CRCT Preparation 1. During a laboratory investigation, Aaron used an oscilloscope to create graphs of sounds that he produced using tuning forks. Which of these four graphs represents the sound that has the lowest volume? A graph 1 B graph 2 C graph 3 D graph 4

CRCT Preparation 2. Which of these graphs represents the sound that has the lowest pitch? A graph 1 B graph 2 C graph 3 D graph 4

CRCT Preparation 2. Which of these graphs represents the sound that has the lowest pitch? A graph 1 B graph 2 C graph 3 D graph 4

A the source of the sound B the amplitude of the sound wave CRCT Preparation 3. If you were conducting an experiment to determine the speed of sound through water, which of the following factors should you keep constant? A the source of the sound B the amplitude of the sound wave C the loudness of the sound D the temperature of the water

A the source of the sound B the amplitude of the sound wave CRCT Preparation 3. If you were conducting an experiment to determine the speed of sound through water, which of the following factors should you keep constant? A the source of the sound B the amplitude of the sound wave C the loudness of the sound D the temperature of the water

A a material that amplifies sound B a material that absorbs sound CRCT Preparation 4. Cletus wants to make ear protectors for people who work around loud jet engines at Hartsfield Airport in Atlanta. Which of the following materials should he experiment with for the best results? A a material that amplifies sound B a material that absorbs sound C a material that transmits sound D a material that produces sound

A a material that amplifies sound B a material that absorbs sound CRCT Preparation 4. Cletus wants to make ear protectors for people who work around loud jet engines at Hartsfield Airport in Atlanta. Which of the following materials should he experiment with for the best results? A a material that amplifies sound B a material that absorbs sound C a material that transmits sound D a material that produces sound Copyright © by Holt, Rinehart and Winston. All rights reserved. Copyright © by Holt, Rinehart and Winston. All rights reserved.

A The strings of the guitar are compressed. CRCT Preparation 5. Which of the following statements about what happens when a guitar is played is true? A The strings of the guitar are compressed. B Particles of air move away from the guitar in all directions. C A longitudinal sound wave moves away from the guitar. D Sound moves away from the guitar in a single direction.

A The strings of the guitar are compressed. CRCT Preparation 5. Which of the following statements about what happens when a guitar is played is true? A The strings of the guitar are compressed. B Particles of air move away from the guitar in all directions. C A longitudinal sound wave moves away from the guitar. D Sound moves away from the guitar in a single direction.

B She produced sound waves that created a sonic boom. CRCT Preparation 6. Jesse walked into a large, dark room and yelled “Hello!” She heard a loud echo of the word almost immediately. Which of the following is a valid conclusion that Jesse could draw from her observations? A She produced sound waves that reflected off of the walls of the room. B She produced sound waves that created a sonic boom. C She produced sound waves that destructively interfered with each other. D She produced sound waves that demonstrated the Doppler effect.

B She produced sound waves that created a sonic boom. CRCT Preparation 6. Jesse walked into a large, dark room and yelled “Hello!” She heard a loud echo of the word almost immediately. Which of the following is a valid conclusion that Jesse could draw from her observations? A She produced sound waves that reflected off of the walls of the room. B She produced sound waves that created a sonic boom. C She produced sound waves that destructively interfered with each other. D She produced sound waves that demonstrated the Doppler effect.

CRCT Preparation 7. According to the table, which of the following statements about the speed of sound is true? A The frequency of a sound wave traveling through hydrogen is higher than the frequency of that wave traveling through helium. B The amplitude of a sound wave traveling through helium is greater than the amplitude of that wave traveling through oxygen. C The speed of a sound wave traveling through hydrogen is greater than the speed of that wave traveling through oxygen. D The pitch of a sound wave traveling through oxygen is higher than the pitch of that wave traveling through hydrogen.

CRCT Preparation 7. According to the table, which of the following statements about the speed of sound is true? A The frequency of a sound wave traveling through hydrogen is higher than the frequency of that wave traveling through helium. B The amplitude of a sound wave traveling through helium is greater than the amplitude of that wave traveling through oxygen. C The speed of a sound wave traveling through hydrogen is greater than the speed of that wave traveling through oxygen. D The pitch of a sound wave traveling through oxygen is higher than the pitch of that wave traveling through hydrogen.

CRCT Preparation 8. You hear a single note played on a violin and the sound of a firecracker exploding. Why is one sound considered music while the other is considered noise? A The violin produces a soft sound, but the firecracker produces a loud sound. B The violin produces sound waves that travel in a single direction, but the firecracker produces sound waves that spread out in all directions. C The violin produces a sound wave that has a repeating pattern, but the firecracker produces a complex sound wave that has no repeating pattern. D The violin produces a sound wave that has a high frequency, but the firecracker produces a sound wave that has a low frequency.

CRCT Preparation 8. You hear a single note played on a violin and the sound of a firecracker exploding. Why is one sound considered music while the other is considered noise? A The violin produces a soft sound, but the firecracker produces a loud sound. B The violin produces sound waves that travel in a single direction, but the firecracker produces sound waves that spread out in all directions. C The violin produces a sound wave that has a repeating pattern, but the firecracker produces a complex sound wave that has no repeating pattern. D The violin produces a sound wave that has a high frequency, but the firecracker produces a sound wave that has a low frequency.