Part One

1. Sound Part One

2. World of Sound • Everyday your world is filled with a multitude of sounds. • Sounds help us communicate. • It can be a warning of danger or simply an enjoyable experience. • Some sounds can be heard by animals but cannot be heard by humans. • Sound Website

3. What is sound? • Sound is a pressure disturbance that moves through a medium in the form of longitudinal waves. • Waves of sound energy move outward in all directions from the source. • Vocal chords and the strings on a guitar vibrate to produce sound waves. • Without energy, there would be no sound.

4. Sound or pressure waves are made up of compressions and rarefactions. • Compressionhappens when particles are forced, or pressed, together. • Rarefaction occurs when particles are given extra space and allowed to expand. • One compression and one rarefaction is one wavelength. • These alternating compressions and rarefactions produce a longitudinal wave.

5. Without a medium there are no particles to carry the sound waves. • In places like space, where there is no atmosphere, there are too few particles to transfer the sound energy.

6. How we hear… • The ear canal channels the waves to your eardrum. • The waves cause your eardrum to vibrate. It passes these vibrations on to the tiny bones in your ear. • These bones vibrate and pass the vibrations into the inner ear the vibrations travel into the cochlea. • Inside the cochlea, there are hundreds of special cells attached to nerve fibers, which can transmit information to the brain. • The brain processes the information from the ear and lets us distinguish between different types of sounds.

8. As you know, there are many different sounds. Fire alarms are loud. Whispers are quiet. Sopranos sing high. Tubas play low. every one has different voice. The differences between sounds are caused by Intensity Loudness Pitch Frequency Tone Why are sounds different?

9. Intensity • Intensity is the amount of energy a sound has over an area. • Amplitude is a measure of energy. • The more energy a wave has, the higher its amplitude. • As amplitude increases, intensity also increases. • As amplitude decreases, intensity also decreases. • Larger amplitude = higher intensity = louder sound.

10. Loudness • We are used to measuring the sounds we hear in loudness (volume). • Loudnesscannot be assigned a specific number, but intensity can. • Intensity is measured in decibels (dB). • Listening to loud sounds, sounds with intensities above 85 decibels, may damage your ears. • 120 decibels is the threshold of pain.

11. Sounds and their Decibels • Defense Siren…130 dB • Rock Concert…110 dB • Lawn Mower…100 dB • Motorcycle…90 dB • Vacuum Cleaner…70 dB • Normal Conversation…60 dB • Background Noise…40 dB • Whisper…20 dB

12. Pitch • Pitch helps us distinguish between low and high sounds. • Pitch depends on the frequency. • High pitches have high frequencies and • Low pitches have low frequencies. • Thunder has a frequency of only 50 Hertz, while a whistle can have a frequency of 1,000 Hertz.

13. Tone • Tone… or sound quality. • When a source vibrates, it actually vibrates with many frequencies at the same time. • Each of those frequencies produces a wave. • Sound quality depends on the combination of different frequencies of sound waves.

14. Sound vs. Noise • A sound must have an identifiable pitch, a good or pleasing quality of tone, and repeating pattern or rhythm to be music. • Anoise on the other hand has no identifiable pitch, no pleasing tone, and no steady rhythm.

15. Ultrasonic and Infrasonic waves • The human ear is able to hear frequencies of 20 Hertz to 20,000 Hertz. • Sounds that are too high for us to hear are called ultrasonic waves. • Sounds that are too low for us to hear are called infrasonic waves. • Mosquito Ringtones

16. Sound Part Two

17. Why do we see lightning before the thunder? • The flash of light from lightning travels at about 300,000,000 m/s or 186,000 miles per second. • Sound travels at about 0.2 miles per second. • It takes sound nearly 5 seconds to travel 1 mile.

18. Speeds of Sound in different mediums Rubber …60 m/s Air at 40 °C… 355 m/s Air at 20 °C …343 m/s Lead …1210 m/s Water …1482 m/s Glass …4540 m/s Copper …4600 m/s Aluminum… 6320 m/s Sound travels faster through materials that are more dense. The speed of sound through the air depends on the temperature. The speed of sound increase by 0.6 m/s with every increase of 1º C. Sound and Speed

19. The Sound Barrier • The speed of sound through warm air at sea level has been measured at 346 m/s • That is the same as a car traveling about 780 mph! • Even most jet airplanes do not travel that fast. • When a plane does go faster than speed of sound, it is said to break the sound barrier and a sonic boom is produced. • Sound Barrier Video

20. Sound and motion • When we are moving, or a source producing a sound is moving, we hear things differently. • You may have noticed that a train whistle gets lower as it passes you. • The whistle is not changing pitch, but you are hearing a change. • This principle is known as the Doppler Effect. • The Doppler effect is named after the Austrian physicist, Christian Johann Doppler, who discovered it.

21. What did Christian Johann Doppler discover? • Doppler claimed that if a sound is getting closer to you, either because its source is approaching you or because you are going towards the source, the sound will seem higher than it is. • If you are heading away from a source or it is going away from you, he believed the sound would seem lower than its actual pitch. • To test his theory, scientists hired 15 trumpeters to play on a moving train. As the train passed by them, they heard a drop in pitch, just like Doppler predicted.

22. TheDoppler Effect • The Doppler Effect happens because distance affects the amount of time it takes you to hear the sound. • The Doppler Effect makes a pitch appear to change when you, or the source, are in motion. • Occurs in all types of waves.

23. The sound is higher coming towards you and lower going away from you.

24. Applications of the Doppler Effect • To learn about stars and galaxies. • We observe light and electromagnetic waves. By using the Doppler Effect we can measure speeds and distances of objects in space. • Radar Detectors • To measure speeds of automobiles. • To measure speed of baseball pitches. Fire Truck Video…Doppler Ball

25. Echoes • An echo is s sound which has been reflected. • Sound reflection best occurs from flat, hard surfaces. • The natural echo of a room is called reverberation. • This is a measure of how much the sound is reflected around the room. • Materials which are soft and uneven (like curtains and carpets) absorb sound much more than they reflect it, and decrease reverberation.

26. Examples of Sonar • In nature, bats emit ultrasonic waves and listen to the echoes to help them know where walls are or to find prey. • Submarines and other boats use special machines that send out and receive ultrasonic waves. These waves help them guide their boats through the water and warn them when another boat is near.

27. Sound Part Three

28. Frequency • The frequency of a wave is different than the speed of a wave. • Frequency refers to how often a wave passes through a certain point. • Speed refers to how fast a wave passes through a certain point.

29. Natural Frequency • Particles vibrate at a specific frequency for every source, this is called natural frequency. • Depends on the size shape and material of the object. • Examples: Steel, brass, and wood all have different natural frequencies.

30. Resonance • Resonance is when objects with the same natural frequency as the vibrating source also begin to vibrate. • Resonance only affects object close to the vibrating source. • A singer can make glass vibrate enough to shatter, just by singing a note with the glass’s natural frequency! • Tuning Forks…Glass Video

31. Beats • Beats occur when two sound waves, with almost identical frequencies, interfere to produce high and low sound levels. • This oscillation of wave amplitude is called a beat. • Tuning Forks

32. Superposition • Superposition is when two or more waves can combine to form a new wave. • If the waves move in opposite directions, they can cancel or form a new wave of lesser or greater amplitude.

33. Wave Interference • Interference is when two or more sound waves from different sources, interact with each other to produce a new wave. • This new wave is a result of superposition.

34. Constructive Interference • Constructive interference is whenthe compressions and the rarefactions of the two waves line up, they strengthen each other and create a wave with a higher intensity. • Higher intensity (louder) • Higher amplitude

35. Destructive Interference • Destructive interference is when the compressions and rarefactions are out of phase, interact and create a wave with a dampened or lower intensity. • Lower intensity (quiet or no sound) • Lower amplitude

36. Super Slinky