2. Sound

3. Review  What do waves transfer?

4. Sounds Close your eyes and listen to these sounds. Click

5. Sound Waves  Mechanical waves- waves that require a medium  Medium – Substance or region through which a wave is transmitted.  Speed of Waves – Depends on the properties of the medium.

6. Longitudinal/Compression Waves

7. Longitudinal Wave wave particles vibrate parallel to the path that the wave travels. Compressional Wave

8.  Compressions The close together part of the wave  Rarefactions The spread-out parts of a wave

9. Properties  Speed  Frequency-Pitch  Intensity-Amplitude-Loudness

10. Speed  The Speed of Sound Depends on the Medium  The time it takes for sounds to reach you does not depend on how loud or high the sound is.  The speed of sound depends only on the medium through which the sound is traveling.  Sounds travel fastest in solids and slowest in gases  Speed of Sound Depends on Temperature  In general, the cooler the medium, the slower the speed of sound  This happens because particles in cool materials move slower than particles in warmer materials  When the particles move slower, they transmit energy more slowly  Therefore, sound travels more slowly in cold air than in hot air MediumSpeed m/s) Air343 Helium1,005 Water1,482 Sea Water1,522 Wood (oak) 3,850 Glass4,540 Steel5,200

11. Sound Travels Through Matter Gases Most of the sounds we hear travel through gases, such as air. Sound waves travel slowly through the air. For example: Sound from a bell, a horn, or an alarm clock travels through the air. Liquids Some sounds that we hear travel through water. Sound waves travel a faster through water than through the air. Sonar is the way to use sounds to locate objects under water. What animals use sonar? Solids Some sounds that we hear travel through solids. Sound waves travel very fast through solids. For example: When you hit a drum, it vibrates, then the sound travels through the air, to your ears.

12. Pitch Pitch is how high or low a sound is  Objects that vibrate slowly, makes a low pitch.  Example- drum.  Objects that vibrate quickly, makes a higher pitch.  Example- flute

13. Frequency Pitch - Pitch Depends on Frequency The pitch of a sound is determined by the frequency of the sound wave. The higher the frequency the higher the pitch Hertz - unit used to measure the frequency of a wave (Hz) Resonance - when two objects naturally vibrate at the same frequency; the sound produced by one object causes the other object to vibrate Resonance

14. Frequency and Hearing  High frequency means more vibrations hitting the ear.  Pitch is how high or how low a sound seems to be.  Healthy humans can hear from 20 Hz to 20,000 Hz  We are most sensitive from 440 Hz to 7,000 Hz.  Ultrasonic sound has a frequency greater than 20,000 Hz.  Dogs (up to 35,000 Hz)  Bats (over 100,000 Hz)  Medical diagnosis  Infrasonic sound has a frequency below 20 Hz; they are felt rather than heard  (earthquakes, heavy machinery).

15. Loudness or Volume  Volume is the loudness or the softness of a sound.  Loud sounds use a lot of energy.  Soft sounds use a little energy.  Example: The harder a drum is hit, the more the drum will vibrate. The more an object vibrates, the louder the sound it makes.

16. Loudness and Amplitude  Loudness is Related to Amplitude  If I strike a drum with a large force, I will hear a loud BOOM!!  Changing the force I strike the drum will change the loudness of the sound that is created  Loudness is how loud or soft a sound is perceived to be.  As you strike the drum harder, you transfer more energy to the drum.  The drum moves with a larger vibration and transfers more energy to the surrounding air.  This increase in energy causes air particles to vibrate farther from their rest positions.

17. Intensity and loudness Intensity- amount of energy in a sound wave. Loudness is human perception of intensity. Loudness is measured on the decibel scale.

18.  Measuring Loudness  The most common unit used to express loudness is the decibel (dB)  Seeing Sound  An oscilloscope is used to graph representations of sound waves  For example, a microphones converts sound waves into an electric current.  The oscilloscope then converts the electric current into graphs Some Common Decibel Levels SoundDecibel level The softest sounds you can hear 0 Whisper20 Purring cat25 Normal conversation60 Lawn mower, vacuum cleaner, truck traffic 80 Chain saw, snowmobile 100 Sandblaster, loud rock concert, automobile horn 115 Threshold of pain120 Jet engine 30 meters away 140 Rocket engine 50 meters away 200

20. Behaviors

21. Doppler Effect the change in frequency due to the relative motion of the wave source and the observer The observed frequency is higher when the source and observer are getting closer. The observed frequency is lower when the source and observer are getting farther away.

22. Doppler Effect  Heard an ambulance go by recently? Remember how the siren's pitch changed as the vehicle raced towards, then away from you? First the pitch became higher, then lower.  This change in pitch results from a shift in the frequency of the sound waves  As an object moves away from you, this causes the waves to be farther apart and to have a lower frequency  As an object moves toward you, this causes the waves to be closer together and to have a higher frequency

23. The Doppler effect – the change in pitch due to a moving wave source. Objects moving toward you cause a higher pitched sound. Objects moving away cause sound of lower pitch. Used in radar by police and meteorologists and in astronomy. The Doppler effect – the change in pitch due to a moving wave source. Objects moving toward you cause a higher pitched sound. Objects moving away cause sound of lower pitch. Used in radar by police and meteorologists and in astronomy.

24. Click here, here, and here here to run simulations of the Doppler Effect. The Doppler Effect can be evident for all types of waves – including light, sound, water, etc…

25. You can view reflection, refraction, diffraction, and interference using both plane and circular waves. Click here to view a movie here clip of an actual ripple tank experiment. The ripple tank simulation found herehere can be used here to investigate wave Behaviors.

26. Reflection of Sound  An echo is reflected sound  Sound reflects from all surfaces of a room  Acoustics is the study of the way sound reflects off of objects in a room  Reverberations – Multiple reflections of sound within a room  The walls of concert halls are designed to make the reflection of sound diffuse  Soft materials dampen sound; hard materials reflect it (echoes and reverberations).

27. Refraction of Sound  Sound waves are refracted when parts of a wave front travel at different speeds  This happens in uneven winds or temperatures  Sound waves tend to bend away from warm ground, since it travels faster in warmer air  On a cold night, the speed of sound is slower near the ground than above, so we can hear over larger distances

28. Refraction of Sound

29. 28 Sound wave diffraction Sound waves can bend around barriers or as they go through an opening. Sound waves have wavelengths from about 15 m down to 2 cm. Many everyday objects are the same size as sound waves – this causes a lot of diffraction. This is why we can hear someone talking to us who is not directly in our line of sight. Sound waves diffract when they pass through doors or move past the edges of walls. Diffraction of sound should not be confused with reflection of sound (echoes).

30. 29 Diffraction of Sound How can the teacher in the corridor hear the school band even though he isn’t in the hall?

31. How We Hear

32. How does the ear work? Sound Waves  Sound waves are sent.  The outer ear “catches the sound waves”.  The middle ear takes the sound waves and “vibrates” the eardrum.  The inner ear sends the messages to the brain. Middle Ear Inner Ear  The brain puts it together and hooray! You hear your favorite song on the radio.brain Outer Ear

34. Different sounds that you hear include (A) noise, (B) pure tones, and (C) musical notes.

35. Music  Music is a combination or sequences of sounds that people enjoy listening to.  Musical instruments make different sounds by plucking the strings.  The shorter the string, the quicker it vibrates producing a high sound.  The longer the string, the slower it vibrates producing a low sound.

36. Musical sound Noise has no pattern. Noise- a sound that consists of a random mix of frequencies Music has a pattern and deliberate pitches. Sound quality describes differences of sounds that have the same pitch and loudness. Every instrument has its own set of overtones.

37. Beats are pulsing variations of loudness caused by interference of sounds of slightly different frequencies.

38. Uses of sound Acoustics – the study of sound. SONAR – Sound Navigation and Ranging, uses echoes(echolocation). Ultrasound imaging Kidney stones & gallstones. SONAR – Sound Navigation and Ranging, uses echoes(echolocation). Ultrasound imaging Kidney stones & gallstones.

39. How You Make Sounds  We use our vocal cords to make sounds in our throat.  When we speak, our vocal cords vibrate.  Place your hand on your throat when you talk, and you can feel the vocal cords vibrate.