1. Bell Ringer What causes sound?

2. Bell Ringer Explain one station from yesterday. How did length affect pitch? How did sound travel through different materials?

3. Waves & Sound

4. Vocabulary Period: Time taken for one complete cycle –Variable: T –Unit: seconds Frequency: Cycles per second –Variable: f –Unit: Hertz (Hz) 1 Hz = 1/second Period and frequency are inverses of each other T = 1/f and f = 1/T

5. Vocabulary Crest: High point of wave Trough: Low point of wave Amplitude: Distance from midpoint to crest –Variable: A –Units: meters Wavelength: Distance from crest to crest –Variable: –Units: meters

6. Vocabulary

7. Catch a Wave Lab

8. Bell Ringer Draw a wave and label its crest, trough, amplitude and wavelength.

9. Types of Waves Transverse: Motion of medium is perpendicular to direction wave travels Longitudinal: Medium moves in the same direction as the wave travels

10. Types of Waves

11. Transverse: Motion of medium is perpendicular to direction wave travels Longitudinal: Medium moves in the same direction as the wave travels

12. The Origin of Sound Produced by the vibration of material objects Pitch: Our impression of the frequency of a sound –A high pitched sound has a high frequency Young people hear pitches with frequencies ranging from 20-20,000 Hz –Infrasonic: Sound waves with frequencies below 20 Hz –Ultrasonic: Sound waves with frequencies above 20,000 Hz

13. Sound in Air Sound travels in the form of longitudinal waves A pulse vibrates through the air as a series of compressions and rarefactions –When molecules compress, they leave areas of low pressure behind them –Other molecules will move into these regions

14. Sound Transmission Sounds can travel through solids, liquids, and gases –Sound travels faster and more efficiently through solids than liquids or gases The speed of sound is different in different materials –At room temperature (20 o C), the speed of sound is 340 m/s Sound cannot travel in a vacuum –No molecules to compress or expand

15. Bell Ringer What is the relationship between pitch and frequency?

16. Wave Speed Speed depends on the medium (material) through which it travels wave speed = wavelength x frequency v =  f

17. Loudness The intensity of a sound is related to the amplitude –Measured by instruments such as an oscilloscope –Unit: decibel (dB) Loudness is how our brain senses the sound (a.k.a. “volume”)

18. Source of SoundLevel (dB) Normal Breathing10 Close Whisper20 Library40 Normal Speech60 Busy Street Traffic70 Subway Train100 Loud Rock Music115 Threshold of Pain120 Jet Engine at 30 m140

19. Interference More than one wave can exist in the same place at the same time Wave effects may be increased, decreased, or cancelled

20. Interference

21. Constructive Interference: Crest of one wave overlaps the crest of another –Results in increased amplitude

22. Interference Destructive Interference: Crest of one wave overlaps the trough of another –Results in cancellation of amplitude

23. Interference and Beats A receiver may hear two sound waves at the same time: –In phase: Compressions and rarefactions overlap each other –Out of phase: Compressions and rarefactions of each wave are offset If the crest of one wave overlaps the trough of another, they will cancel Beats: The periodic variation in the loudness of a sound –Produced from two sounds of slightly different frequencies

24. Interference and Beats

26. Bell Ringer If a 400 Hz sound wave has a wavelength of 3.71m as it travels through water. What is the speed of sound in water? How does this compare with the speed of sound in air?

27. Standing Waves Created when a wave reflects on itself Nodes: Parts of a standing wave which remain stationary Antinodes: Positions on a standing wave with the largest amplitudes Node Antinodes

28. Standing Waves Harmonics –To determine the harmonic of a standing wave, count the antinodes. 1 st Harmonic: 2 nd Harmonic: 3 rd Harmonic: 4 th Harmonic:

29. Doppler Effect The apparent change in frequency due to the motion of the source or receiver of the wave Applies to both sound and light

30. Doppler Effect

31. Bow Waves Wave shape produced when an object moves faster than the speed of the wave surrounding it –Two-dimensional

32. Shock Waves Similar to a bow wave, except three- dimensional –Cone shaped

33. Shock Waves An object exceeding the speed of sound will produce a shock wave When the compressed air at the edges of the shock wave reach the ground, a sonic boom is heard –The object does not have to initially make any sound in order to produce a sonic boom –i.e.) The cracking of a whip is actually a mini sonic boom!

34. Forced Vibrations Sounds will be more intense if additional material is made to vibrate –i.e. A guitar would not be audible if the sound was not transmitted through its wooden body

35. Natural Frequency Frequency at which the smallest amount of energy is required to produce forced vibrations Any object made of elastic material will vibrate at its own frequency when disturbed –Natural frequency depends on the elasticity and the shape of the object

36. Resonance When the frequency of a forced vibration matches the object’s natural frequency –Dramatically increases the amplitude of the sound wave i.e.) Pumping a swing

37. Resonance