Chapter 6. Waves and Sound 6.1 Waves-Types and Properties 6.2 Aspects of Wave Propagation 6.3 Sound 6.4 Production of Sound 6.5 Propagation of Sound 6.6 Perception of Sound Sound Medicine ESWL being used on a Kidney stone: The Wave pulse is focused onto the stone because the stone and the spark producing the pulse are located at the foci of the ellipsoidal reflector.

6.1 Wave-Types and Properties Wave : A traveling disturbance consisting of coordinated vibrations that transmit energy with no net movement of matter. A wave traveling on a ropelike spring

Wave 1. wave pulse: 짧은 시간에 지나가는 파동: 풍선 터지는 소리, 쓰나미, 사진기 플래쉬 2 Wave 1. wave pulse: 짧은 시간에 지나가는 파동: 풍선 터지는 소리, 쓰나미, 사진기 플래쉬 2. continuous wave: 일정하게 되풀이하는 파동: 소리굽쇠, 소리, 햇빛 (a) Successive views of a wave pulse as it travels on a rope. (b) A continuous wave traveling on a rope.

Transverse Wave (횡파): A wave in which the oscillations are perpendicular to the direction the wave travels. Ex: waves on a rope, electromagnetic waves, some seismic waves. Longitudinal Wave (종파): A wave in which the oscillations are along the direction the wave travels. Ex: sound in the air, some seismic waves.

철사에서 파동의 속력: 선 밀도 힘을 크게 하면 파동이 빨라진다 예) 기타, 피아노의 줄 철사에서 파동의 속력: 선 밀도 힘을 크게 하면 파동이 빨라진다 예) 기타, 피아노의 줄 Ex 6.1 A student stretches a Slinky out on the floor to a length of 2m. The force needed to keep the Slinky stretched is measured and is found to be 1.2N; the Slinky’s mass is 0.3kg. What is the speed of any wave sent down the Slinky by the student?

The speed of sound in air or any other gas depends on the ratio of the pressure of the gas to the density of the gas But for each gas, the ratio in turns depends only on the temperature. The speed of sound is lower at high altitude, not because the air is thinner, but because it is colder. Ex 6.2 What is the speed of sound in air at room temperature? 헬륨에서: CO2에서:

연속 파동의 몇 가지 성질 Amplitude (진폭): The maximum displacement of points on a wave, measured from the equilibrium position. Wavelength (파장): The distance between two successive like point on a wave. For example, the distance between two adjacent peaks or two adjacent valleys. Frequency (진동수): The number of cycles of a wave passing a point per unit time. The number of oscillations per second in the wave. *Audible sound (가청음파): 20Hz-20,000Hz

Wave with large amplitude Transverse waves with different combinations of wavelength and amplitude.

The amplitude of a longitudinal wave on a Slinky equals the greatest lateral displacement of the coils. If five cycles of a wave pass by a point in 1 second, and the wavelength of a wave is 0.03m, then the wave is traveling 0.15m/s.  

Two examples of complex waves Two examples of complex waves. The lower wave, a “square wave,” is used in many electronic devices. Ex 6.3 Before a concert, musicians in an orchestra tune their instruments to the note A, which has a frequency of 440Hz. What is the wavelength of this sound in air at room temperature? v = 344m/s

6.2 Aspect of Wave Propagation (a) A wavefront (파면) is used to show how a pulse spread over water. (b) The same wave pulse represented with wave rays. The rays point in the direction the wave travels and are perpendicular to the wavefront. Wavefronts and rays for a continuous wave on a surface. Far away from the wave source the wavefronts are nearly straight, and the ray are nearly parallel.

440Hz의 소리굽쇠: 매초당 440개의 파면을 만든다. 3차원 파동에서 원에서 충분히 먼 거리가 되면 파면은 평면형 Resonance

Reflection (반사): A wave is reflected whenever it reaches a boundary of its medium or encounters an abrupt change in the properties of its medium. 파동이 매질의 경계면(밀도가 크게 변함)에서 반사 The reflection of water ripples off the side of a pool. Both models of the wave show that the reflected wave appears to diverge from a point behind the wall, called the image.

A sound wave reflecting off a concave surface A sound wave reflecting off a concave surface. The reflected rays converse toward a point, indicating that the wave’s amplitude increases. Parabolic “dish” antennas focus radio waves by reflections.

The focusing property of an ellipse The focusing property of an ellipse. Each ray of a wave produced at one focus reflects off the ellipse and passes through the other focus. Doppler Effect (도플러 효과): an apparent change in the frequency of a wave due to motion of the source of a wave or the receiver.

The Doppler effect with moving observers The Doppler effect with moving observers. The person in the car on the left hears a higher frequency than the pedestrian. The person in the car on the right hears a lower frequency.

Simple echolocation. You can determine the distance to the cliff by timing the echo. Radar unit in use.

(a) Shock wave is produced when the speed of a wave source exceeds the wave speed. Parts of the wavefronts combine along the two black lines to form a V—shaped wavefront. (b) The jet-powered car Thrust SSC traveling faster than sound on 25 September 1997. Dust can be seen being kicked up by the shock wave extending away from the car on both sides.

Diffraction: Diffraction occurs as a wave moves through an opening in a barrier. The diffraction of water waves as it passes through an opening in a barrier. The wavefronts spread out to the sides after passing through. Diffraction of water waves passing through a narrow gap in a barrier. Short-wavelength wave (left) are nor diffracted as much as long-wavelength waves(right) passing through an opening of the same size.

Here is a simple way to experience diffraction of sound Here is a simple way to experience diffraction of sound. Stand near an open window or door of a building in which a continuous sound is being produced, such as recorded music. Move back and forth past the opening, and notice that the sound is loudest when you are directly in front of the opening but that you can hear it when you are well off to the one side.

Interference Interference arises when two continuous waves, usually with the same amplitude and frequency, arrive at the same place. Interference of two waves Interference pattern of water waves from two nearby sources. The thin lines of calm water indicate destructive interference. Because these lines are regions of large-amplitude waves, caused by constructive interference.

6. 3 Sound: 고체, 액체, 기체를 통해 진행. 말할 때 머리의 뼈나 조직을 통해 전해온 소리를 듣는다 고체에서는 분자 사이의 힘이 크므로 음속이 빠르다

A representation of part of the sound wave emitted by a turning fork A representation of part of the sound wave emitted by a turning fork. The air pressure is increased in each compression and reduced in each expansion. 소리의 파형: 공기의 압력의 변화를 나타낸 그래프 순음(pure tone): sine파 복합음(complex): 반복성은 있지만 사인파형이 아니다. 잡음(noise): 반복성이 없는 무작위적인 파형

가청음파: 초저파:20Hz – 20,000Hz: 초음파 Sound Applications: 초음파(16-150kHz) 이용: 돌고래, 박쥐 초음파의 의학적 이용: 초음파 진단기, 초음파 쇄석법(신장결석)

6.4 Production 1) 진동에 의해 공기 압력변화가 발생 타악기: 드럼, 트라이 앵글, 실로폰 2) 줄을 진동시켜 발생 현악기: 기타, 바이올린, 피아노 공명관을 이용하여 소리를 증폭 Sound production in a piano. The hammer creates a wave pulse that oscillates back and forth on the piano wire. The pulse cases the soundboard to vibrate at the frequency of the pulse’s oscillation.

Sound production in a flute Sound production in a flute. The musician causes a sound (pressure) to oscillate back and forth in the tube. Each time the pulse reaches the right end, it sends out a compression-part of the sound that we hear Opening a side hole shortens the path of the pulse, thereby increasing the frequency. All singers produce sound by making their vocal cords vibrate. The position of the jaw, the size of the mouth opening, and the other factors also influence the sound.

6.5 Propagation of Sound The amplitude is inversely proportional to the distance from the sound source. 진폭은 소리의 샘으로부터 거리에 반비례 잔향시간: 진폭이 1/1,000로 줄어드는데 걸리는 시간

Symphony Hall in Boston is very successful at using reverberation to enhance sound. A series of steady sounds, such as spoken syllables, are heard (a) in an open field and (b) in a room. Reverberation in the room causes the sounds to merge. This tends to blend musical notes and makes speech more difficult to understand.

6.6 Perception of Sound 소리의 높낮이: 진동수 소프라노: 높다 베이스: 낮다 소리의 세기(크기): 진폭 소리의 음질: 파형 바이올린, 플루트: 음질이 다르다 악기와 음성에서 소리의 높낮이

소리의 세기: 소리의 진폭에 따라 다르다 소리의 수준(sound level): 데시벨(dB): 0dB(청력의 한계)-120dB(고통의 한계) 사람이 들을 수 있는 가장 작은 소리: 사람이 들을 수 있는 가장 큰 소리:

85dB 이상: 듣기 힘들고 120dB 이상: 고통스럽고 청각장애 가능성 Ten equivalent sources sound about twice as loud as one

가청 음파: 20Hz-20,000Hz 민감한 주파수: 1,000Hz-5,000Hz A sound-level meter

Tone Quality: The tone quality of a sound depends primarily on the waveform of the sound wave. 소리의 음질은 소리의 파형에 의해 결정 High-fidelity sound equipment must be able to reproduce high-frequency harmonics. This equalizer has 10 frequency bands that span the range from 20Hz to 20 KHz. 하이파이 음향장비: 고 진동수의 배음 재생 20Hz-20,000Hz에서 10개의 진동수 대역

6장 연습문제 물어보기: 19, 21, 24, 26, 풀어보기: 5, 11, 13, 15, 17, 19, 21, 23, 25