Slide 1

Waves and SoundBasic Sound Wave CharacteristicsSound is produced when something vibrates in a medium that can carry the vibration.In most cases the medium which with we are most familiar is AIR.However other mediums also carry vibration waves solids and liquids also can carry vibrationMechanical waveLongitudinal wave

Diagram of a Sound Waveobjects vibrate, causing air molecules in their vicinity to vibrate, which then radiates outward from object

http://www.glenbrook.k12.il.us/gbssci/phys/mmedia/waves/tfl.gif

tuning fork with stroblightSpeed of SoundDepends only on the medium the wave is traveling throughMedium can be affected by temperature, with greater temp = greater speedMore elastic mediums = greater speed (**elasticity means ability of molecules to move but also to resume their original position)Speed of sound animationIn various mediums:Diamond 14,000 m/sSteel 5,100 m/sWater 1,300 m/sAir 340 m/sThunder vs Lightning

LoudnessPhysiological sensationIntensity proportional to amplitude2 Measured decibels (dB)Higher dBs louder volumeLogarithmic, based on powers of 1085 dB + cause hearing loss over time180 dB cause immediate damage8 hours at 90 dB causes damage

The chart on the left is a representation of different sounds around us and their volume in decibels.

The picture above is a wave file of someone singing.

Pitch

A measure of how high or low a sound isPitch depends on the frequency of a sound waveFor example,

Low pitch Low frequency Longer wavelength

High pitch High frequency Shorter wavelength

Frequency Audible RangesHumansCan hear 20 Hz to 20 KHzBest hearing within 100 2000 HzAnimalsDogs can hear up to 50 KHzCats can hear up to 60 KHzBats and whales can make and hear up to 120 KHzThe Doppler EffectFire Engine sirenThe Doppler Effect - Wavelength Shift Due to Motion.

Big Bang Doppler Effect

11Boundary BehaviorsA boundary is a place where conditions change.12Bouncing back of a wave after it strikes a barrier that does not absorb the energy.An echo is a sound wave that has beenreflectedReflection

Barrier

The angle of the reflected wave to the normal must equal the angle of the incident wave to the normal.Used to locate underwater objects and distances.***Reflection**

sonarSonograms: Ultrasonic waves (about 20,000 Hz) used to create images of fetuses in the womb

Regular sonogram 3D sonogramWhy does the pencil appear to be broken when placed in a beaker of water??

Refraction: Bending of waves due to a change in speed (this occurs because the wave changes mediums)

Refraction

DiagramsfastslowFast to slow, bends towards normalslowfastSlow to fast, bends away from normalIncident raynormalrefracted raywavefrontsThe wave approaching a boundary is called the incident wave. The wave moving away from a boundary is the reflected or refractedThe normal is a line perpendicular to the boundary, marked where an incident wave or ray crosses

DiffractionBending of waves around the edge of a barrier, or through openings in a barrier

In sound, this is called damping occurs even through airDef. - Interference is the result of two or more waves passing through a medium at the same time.

There are two types of Wave interference:1. Constructive Interference2. Destructive InterferenceWave interferenceConstructive Interference: two crests meet and make a wave with a bigger amplitude.Wave interference

Destructive Interference: one crest & one trough meet and make a wave with a smaller amplitude.Wave interference

Interference in SoundGuys ear is where a compression of one sound wave meets the rarefaction of another does he hear the sound loudly or softly?

Guys ear is where compression meets compression does he hear the sound loudly or softly?Wave Motion Interference Ripple TankSound PhETMusicOne single frequency played on one instrument would not be very excitingMusic is made up of combined sound waves of different frequencies, from one or more instrumentsWhole number ratios between frequencies necessary for music to sound pleasantCauses regular and repeating resultant waves3rd harmonic is 320 Hz, 4th harmonic is 640 Hz, 5th harmonic is 960 Hz (a twelfth above 3rd Harmonic, E3)

Harmonies, Octaves, and Fifths

NoiseResults when there is no discernible pattern of frequencies (no whole number ratios, or regular or repeated patterns)

Beatsfluctuations in the intensity produced by the superposition of 2 waves at slightly different frequenciesBeat frequency is how many fluctuations in volume there areper second,measured in HzTuning instruments

ResonanceAlmost everything can vibrate, and everything has at least one natural frequencyDrop a pencil, you make it vibratePluck a guitar string, it vibratesWhen applied frequency (from dropping or plucking) matches natural frequency, constructive interference results in increased amplitude and a standing wave is formed this is resonanceNoise comes from objects with many, irregular frequencies that produce complex sound waves with no patternApplications of ResonanceThe Brown NoiseYouTube - The Brown Note Clip

Shattering a glassYouTube - breaking a wine glass using resonance

Tacoma Narrows BridgeYouTube - Tacoma Narrows Newsreel3. Frieda the fly flaps its wings back and forth 121 times each second. The period of the wing flapping is ____ sec.4. Olive Udadi accompanies her father to the park for an afternoon of fun. While there, she hops on the swing and begins a motion characterized by a complete back-and-forth cycle every 2 seconds. The frequency of swing is _________. 5. A child in a swing makes one complete back and forth motion in 3.2 seconds. This statement provides information about the child's

a. speed b. frequencyc. period2. As the frequency of a wave increases, the period of the wave ___.a. decreases b. increasesc. remains the same6. The time required for the sound waves (v = 340 m/s) to travel from the tuning fork to point A is ____ .

a. 0.020 secondb. 0.059 secondc. 0.59 secondd. 2.9 second

7. An ocean wave has an amplitude of 2.5 m. Weather conditions suddenly change such that the wave has an amplitude of 5.0 m. The amount of energy transported by the wave is __________.a. halved c. quadrupledb. doubledd. remains the same

8. A teacher attaches a slinky to the wall and begins introducing pulses with different amplitudes. Which of the two pulses (A or B) below will travel from the hand to the wall in the least amount of time? Justify your answer.

9. The teacher then begins introducing pulses with a different wavelength. Which of the two pulses (C or D) will travel from the hand to the wall in the least amount of time ? Justify your answer.

11. Two waves are traveling through the same container of nitrogen gas. Wave A has a wavelength of 1.5 m. Wave B has a wavelength of 4.5 m. The speed of wave B must be ________ the speed of wave A.

One-ninthc. the same asOne-thirdd. three times larger than10. The speed of a wave depends upon (i.e., is causally affected by) ...

a. the properties of the medium through which the wave travels b. the wavelength of the wave.c. the frequency of the wave.d. both the wavelength and the frequency of the wave.12. The number of nodes in the standing wave shown in the diagram at the right is ____.

a. 6b. 7c. 8d. 1413. Of all the labeled points, destructive interference occurs at which point(s) ____.

Lenses refract waves to a focal pointCinema Classics (Side C)61, 62Deep water is FASTER than shallow water