Embed Size (px)
Citation preview
Chapter 17Chapter 17
Mechanical Waves and SoundMechanical Waves and Sound
Chapter 17Chapter 17
*Mechanical wave- disturbance in matter *Mechanical wave- disturbance in matter that carries energy from one place to that carries energy from one place to anotheranother
*Medium- material through which a wave *Medium- material through which a wave travelstravels
A mechanical wave is created when a A mechanical wave is created when a source of energy causes a vibration to source of energy causes a vibration to travel through a medium.travel through a medium.
The three main types of mechanical waves The three main types of mechanical waves are transverse waves, longitudinal waves, are transverse waves, longitudinal waves, and surface waves.and surface waves.
Chapter 17Chapter 17
*Transverse wave- wave that causes the *Transverse wave- wave that causes the medium to vibrate at right angles to the medium to vibrate at right angles to the direction in which the wave travelsdirection in which the wave travels *Crest- highest point above the rest position*Crest- highest point above the rest position *Trough- lowest point below the rest *Trough- lowest point below the rest
positionposition
Chapter 17Chapter 17 *Longitudinal wave- wave in which the *Longitudinal wave- wave in which the
vibration of the medium is parallel to the vibration of the medium is parallel to the direction the wave travelsdirection the wave travels *Compression- an area where the particles in a *Compression- an area where the particles in a
medium are spaced close togethermedium are spaced close together *Rarefaction- an area where the particles in a *Rarefaction- an area where the particles in a
medium are spread outmedium are spread out
Chapter 17Chapter 17
*Surface wave- wave that travels *Surface wave- wave that travels along a surface separating two mediaalong a surface separating two media
Chapter 17Chapter 17
*Periodic motion- any motion *Periodic motion- any motion that repeats at regular time that repeats at regular time intervalsintervals
*Period- time required for one *Period- time required for one cyclecycle
*Frequency- number of complete *Frequency- number of complete cycles in a given timecycles in a given time
Chapter 17Chapter 17
*Hertz- cycles per second; *Hertz- cycles per second; frequency measurementfrequency measurement
A wave’s frequency equals the A wave’s frequency equals the frequency of the vibrating source frequency of the vibrating source producing the wave.producing the wave.
*Wavelength- distance between a *Wavelength- distance between a point on one wave and the same point on one wave and the same point on the next cycle of the wavepoint on the next cycle of the wave Increasing the frequency decreases Increasing the frequency decreases
the wavelength.the wavelength.
Chapter 17Chapter 17
FORMULA (speed of waves)FORMULA (speed of waves) Speed (Speed (vv); wavelength (); wavelength (λλ); );
frequency (frequency (ff)) v = λ·fv = λ·f
Velocity of Propagation- speed at Velocity of Propagation- speed at which a wave front passes which a wave front passes through a medium, relative to through a medium, relative to the speed of light.the speed of light.
Chapter 17Chapter 17
If you assume that waves are If you assume that waves are traveling at a constant speed, traveling at a constant speed, then wavelength is inversely then wavelength is inversely proportional to frequency.proportional to frequency.
*Amplitude- maximum *Amplitude- maximum displacement of the medium displacement of the medium from its rest positionfrom its rest position
The more energy a wave has, the The more energy a wave has, the greater is its amplitude.greater is its amplitude.
Chapter 17Chapter 17 *Reflection- wave bounces off a *Reflection- wave bounces off a
surface that it cannot pass throughsurface that it cannot pass through Reflection does not change the speed Reflection does not change the speed
or frequency of a wave, but the wave or frequency of a wave, but the wave can be flipped upside down.can be flipped upside down.
*Refraction- bending of a wave as it *Refraction- bending of a wave as it enters a new medium at an angleenters a new medium at an angle
When a wave enters a medium at an When a wave enters a medium at an angle, refraction occurs because one angle, refraction occurs because one side of the wave moves more slowly side of the wave moves more slowly than the other side.than the other side.
Chapter 17Chapter 17 *Diffraction- bending of a wave as it *Diffraction- bending of a wave as it
moves around an obstacle or passes moves around an obstacle or passes through a narrow openingthrough a narrow opening A wave diffracts more if its wavelength is A wave diffracts more if its wavelength is
large compared to the size of an opening or large compared to the size of an opening or obstacle.obstacle.
*Interference- two or more waves *Interference- two or more waves overlap and combine togetheroverlap and combine together *Constructive interference- occurs when *Constructive interference- occurs when
two or more waves combine to produce a two or more waves combine to produce a wave with a larger displacementwave with a larger displacement
*Destructive interference- occurs when *Destructive interference- occurs when two or more waves combine to produce a two or more waves combine to produce a wave with a smaller displacementwave with a smaller displacement
Chapter 17Chapter 17
*Standing wave- wave that appears to stay *Standing wave- wave that appears to stay in one place, and not moving through a in one place, and not moving through a mediummedium
*Node- point on a standing wave that has *Node- point on a standing wave that has no displacement from the rest positionno displacement from the rest position
*Antinode- point where a crest or trough *Antinode- point where a crest or trough occurs midway between two nodesoccurs midway between two nodes
A standing wave forms only if half a A standing wave forms only if half a wavelength or a multiple of half a wavelength or a multiple of half a wavelength fits exactly into the length of a wavelength fits exactly into the length of a vibrating cord.vibrating cord.
Chapter 17Chapter 17
*Sound waves- longitudinal waves; *Sound waves- longitudinal waves; compressions and rarefactions compressions and rarefactions that travel through a mediumthat travel through a medium
Many behaviors of sound can be Many behaviors of sound can be explained using a few properties- explained using a few properties- speed, intensity and loudness, and speed, intensity and loudness, and frequency and pitch.frequency and pitch.
The speed of sound is 342 meters The speed of sound is 342 meters per second in dry air at 20ºC.per second in dry air at 20ºC.
Chapter 17Chapter 17
*Intensity- rate at which a wave’s *Intensity- rate at which a wave’s energy flows through a given energy flows through a given areaarea
*Loudness- physical response to *Loudness- physical response to the intensity of sound, modified the intensity of sound, modified by physical factorsby physical factors
*Pitch- frequency of a sound as *Pitch- frequency of a sound as you perceive it; it depends upon you perceive it; it depends upon a wave’s frequency.a wave’s frequency.
Chapter 17Chapter 17
Ultrasound is used in a variety of Ultrasound is used in a variety of applications, including sonar and applications, including sonar and ultrasound imaging.ultrasound imaging.
*Sonar- technique for determining the *Sonar- technique for determining the distance to an object under water.distance to an object under water.
*Doppler effect- change in sound *Doppler effect- change in sound frequency caused by motionfrequency caused by motion
As a source of sound approaches, an As a source of sound approaches, an observer hears a higher frequency. When observer hears a higher frequency. When the sound source moves away, the the sound source moves away, the observer hears a lower frequency.observer hears a lower frequency.
