Unit 2 Lesson 2 Interactions of Sound Waves

Unit 2 Lesson 2 Interactions of Sound Waves Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 2 Interactions of Sound Waves Some Like It Hot What affects the speed of sound? • There are two main factors that affect the speed of sound: the type of medium the sound travels through, and the temperature of the medium. • If we know these factors, we can predict the speed of sound. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 2 Interactions of Sound Waves What affects the speed of sound? • The speed of sound depends on the type of matter, or medium, through which sound travels. • The state of matter also affects sound waves. • Sound travels fastest through solids, slower through liquids, and slowest through gases. • The more packed together the particles are, the faster the wave will travel. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 2 Interactions of Sound Waves What affects the speed of sound? • The speed of sound depends on the temperature of a medium. • Sound travels faster at higher temperatures than at lower ones. • Particles in a material move more quickly at higher temperatures and transfer energy faster. • Sound moves faster at higher temperatures and slower at cooler temperatures. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 2 Interactions of Sound Waves Hello? How do sound and matter interact? • Sound waves do not travel easily through all matter. • Sound may bounce away from some surfaces. Sound may be absorbed by other sources or transmitted through a barrier • Reflection is the bouncing back of a wave when it hits a barrier. Sound waves reflect best off smooth, hard surfaces. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 2 Interactions of Sound Waves How do sound and matter interact? • Some matter absorbs sound waves better than other matter. • A rough wall will absorb sound better than a smooth wall will. • Soft materials, such as rugs and drapes, will absorb sound better than hard surfaces will. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 2 Interactions of Sound Waves How do sound and matter interact? • How will sound waves travel differently in each room? Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 2 Interactions of Sound Waves What is an echo? • An echo is a reflected sound wave. • The strength of the echo depends on the reflecting surface. • Echoes can be reduced using soft materials that absorb the sound waves. • Echoes can also be reduced using rough surfaces that scatter the sound waves. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 2 Interactions of Sound Waves What is an echo? • Some animals—such as dolphins, bats, and beluga whales—use echoes to hunt for food and find objects in their path. • The use of reflected sound to find objects is called echolocation. • People use a type of echolocation called sonar (sound navigation and ranging). • Sonar is electronic echolocation used to locate objects underwater. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 2 Interactions of Sound Waves What is an echo? • How do bats use echolocation? Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 2 Interactions of Sound Waves Boom! How do sound waves interact with each other? • Interference happens when two or more waves overlap and combine to form one wave. • In music, beats happen when two sound waves with nearly equal frequencies interfere. • Since the frequencies are not quite equal, they form a repeating pattern of constructive and destructive interference that sounds loud and soft. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 2 Interactions of Sound Waves How do sound waves interact with each other? • When constructive interference occurs, waves overlap and combine to form a wave with a larger amplitude, or height. • Constructive waves can cause very loud sounds, such as sonic booms. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 2 Interactions of Sound Waves How do sound waves interact with each other? • In destructive interference, waves combine to form a wave with a smaller amplitude. • The sound will be softer because the amplitude is decreased. • Noise cancelling headphones use destructive interference. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 2 Interactions of Sound Waves How does interference cause sonic booms? • Jet planes moving faster than the speed of sound can produce a very loud sound called a sonic boom. • This sound can rattle and even break windows. • When a jet travels very fast, it catches up to its own sound. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 2 Interactions of Sound Waves How does interference cause sonic booms? • The waves pile up as a result of constructive interference. • This interference forms a high pressure area called a sound barrier. • If a jet travels fast enough, it breaks through the barrier and forms a single shock wave that is heard as a loud boom. • The jet must travel at supersonic speeds, or speeds faster than the speed of sound. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 2 Interactions of Sound Waves How does interference cause sonic booms? • How does this jet create a sonic boom? Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 2 Interactions of Sound Waves Good Vibrations What is resonance? • Resonance happens when a sound wave matches the natural frequency of an object and causes the object to vibrate. • If a sound wave in the room forces air in a seashell to vibrate at its natural frequency, resonance occurs. • This resonance results in a big vibration that sounds like the ocean when you hear it. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 2 Interactions of Sound Waves Where can resonance occur? • All objects have a frequency, or set of frequencies, at which they vibrate. • These are called natural frequencies, or resonant frequencies. • Resonance will happen whenever an object vibrating at or near the natural frequency of a second object causes the second object to vibrate as well. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 2 Interactions of Sound Waves Where can resonance occur? • Resonance is important for making music. • Vibrations make a sound that gets louder when it forms a standing wave inside the instrument. • A standing wave is a pattern of vibration that looks like the wave is standing still. • Resonance occurs when standing waves are formed. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 2 Interactions of Sound Waves Where can resonance occur? • Resonance can even occur in buildings, towers, and bridges. • Simple activities such as marching can create resonance to cause a bridge to sway or collapse. • Engineers plan their designs to prevent resonance that could collapse a structure. • Overlapping plates cause friction to keep resonance from becoming destructive. Copyright © Houghton Mifflin Harcourt Publishing Company