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Chapter 17 Mechanical Waves and Sound. Chapter 17 *Mechanical wave- disturbance in matter that carries energy from one place to another *Mechanical wave-

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Presentation on theme: "Chapter 17 Mechanical Waves and Sound. Chapter 17 *Mechanical wave- disturbance in matter that carries energy from one place to another *Mechanical wave-"— Presentation transcript:

1 Chapter 17 Mechanical Waves and Sound

2 Chapter 17 *Mechanical wave- disturbance in matter that carries energy from one place to another *Mechanical wave- disturbance in matter that carries energy from one place to another *Medium- material through which a wave travels *Medium- material through which a wave travels A mechanical wave is created when a source of energy causes a vibration to travel through a medium. A mechanical wave is created when a source of energy causes a vibration to travel through a medium. The three main types of mechanical waves are transverse waves, longitudinal waves, and surface waves. The three main types of mechanical waves are transverse waves, longitudinal waves, and surface waves.

3 Chapter 17 *Transverse wave- wave that causes the medium to vibrate at right angles to the direction in which the wave travels *Transverse wave- wave that causes the medium to vibrate at right angles to the direction 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 position *Trough- lowest point below the rest position

4 Chapter 17 *Longitudinal wave- wave in which the vibration of the medium is parallel to the direction the wave travels *Longitudinal wave- wave in which the vibration of the medium is parallel to the direction the wave travels *Compression- an area where the particles in a medium are spaced close together *Compression- an area where the particles in a medium are spaced close together *Rarefaction- an area where the particles in a medium are spread out *Rarefaction- an area where the particles in a medium are spread out

5 Chapter 17 *Surface wave- wave that travels along a surface separating two media *Surface wave- wave that travels along a surface separating two media

6 Chapter 17 *Periodic motion- any motion that repeats at regular time intervals *Periodic motion- any motion that repeats at regular time intervals *Period- time required for one cycle *Period- time required for one cycle *Frequency- number of complete cycles in a given time *Frequency- number of complete cycles in a given time

7 Chapter 17 *Hertz- cycles per second; frequency measurement *Hertz- cycles per second; frequency measurement A waves frequency equals the frequency of the vibrating source producing the wave. A waves frequency equals the frequency of the vibrating source producing the wave. *Wavelength- distance between a point on one wave and the same point on the next cycle of the wave *Wavelength- distance between a point on one wave and the same point on the next cycle of the wave Increasing the frequency decreases the wavelength. Increasing the frequency decreases the wavelength.

8 Chapter 17 FORMULA (speed of waves) FORMULA (speed of waves) Speed (v); wavelength (λ); frequency (f) Speed (v); wavelength (λ); frequency (f) v = λ·f v = λ·f Velocity of Propagation- speed at which a wave front passes through a medium, relative to the speed of light. Velocity of Propagation- speed at which a wave front passes through a medium, relative to the speed of light.

9 Chapter 17 If you assume that waves are traveling at a constant speed, then wavelength is inversely proportional to frequency. If you assume that waves are traveling at a constant speed, then wavelength is inversely proportional to frequency. *Amplitude- maximum displacement of the medium from its rest position *Amplitude- maximum displacement of the medium from its rest position The more energy a wave has, the greater is its amplitude. The more energy a wave has, the greater is its amplitude.

10 Chapter 17 *Reflection- wave bounces off a surface that it cannot pass through *Reflection- wave bounces off a surface that it cannot pass through Reflection does not change the speed or frequency of a wave, but the wave can be flipped upside down. Reflection does not change the speed or frequency of a wave, but the wave can be flipped upside down. *Refraction- bending of a wave as it enters a new medium at an angle *Refraction- bending of a wave as it enters a new medium at an angle When a wave enters a medium at an angle, refraction occurs because one side of the wave moves more slowly than the other side. When a wave enters a medium at an angle, refraction occurs because one side of the wave moves more slowly than the other side.

11 Chapter 17 *Diffraction- bending of a wave as it moves around an obstacle or passes through a narrow opening *Diffraction- bending of a wave as it moves around an obstacle or passes through a narrow opening A wave diffracts more if its wavelength is large compared to the size of an opening or obstacle. A wave diffracts more if its wavelength is large compared to the size of an opening or obstacle. *Interference- two or more waves overlap and combine together *Interference- two or more waves overlap and combine together *Constructive interference- occurs when two or more waves combine to produce a wave with a larger displacement *Constructive interference- occurs when two or more waves combine to produce a wave with a larger displacement *Destructive interference- occurs when two or more waves combine to produce a wave with a smaller displacement *Destructive interference- occurs when two or more waves combine to produce a wave with a smaller displacement

12 Chapter 17 *Standing wave- wave that appears to stay in one place, and not moving through a medium *Standing wave- wave that appears to stay in one place, and not moving through a medium *Node- point on a standing wave that has no displacement from the rest position *Node- point on a standing wave that has no displacement from the rest position *Antinode- point where a crest or trough occurs midway between two nodes *Antinode- point where a crest or trough occurs midway between two nodes A standing wave forms only if half a wavelength or a multiple of half a wavelength fits exactly into the length of a vibrating cord. A standing wave forms only if half a wavelength or a multiple of half a wavelength fits exactly into the length of a vibrating cord.

13 Chapter 17 *Sound waves- longitudinal waves; compressions and rarefactions that travel through a medium *Sound waves- longitudinal waves; compressions and rarefactions that travel through a medium Many behaviors of sound can be explained using a few properties- speed, intensity and loudness, and frequency and pitch. Many behaviors of sound can be explained using a few properties- speed, intensity and loudness, and frequency and pitch. The speed of sound is 342 meters per second in dry air at 20ºC. The speed of sound is 342 meters per second in dry air at 20ºC.

14 Chapter 17 *Intensity- rate at which a waves energy flows through a given area *Intensity- rate at which a waves energy flows through a given area *Loudness- physical response to the intensity of sound, modified by physical factors *Loudness- physical response to the intensity of sound, modified by physical factors *Pitch- frequency of a sound as you perceive it; it depends upon a waves frequency. *Pitch- frequency of a sound as you perceive it; it depends upon a waves frequency.

15 Chapter 17 Ultrasound is used in a variety of applications, including sonar and ultrasound imaging. Ultrasound is used in a variety of applications, including sonar and ultrasound imaging. *Sonar- technique for determining the distance to an object under water. *Sonar- technique for determining the distance to an object under water. *Doppler effect- change in sound frequency caused by motion *Doppler effect- change in sound frequency caused by motion As a source of sound approaches, an observer hears a higher frequency. When the sound source moves away, the observer hears a lower frequency. As a source of sound approaches, an observer hears a higher frequency. When the sound source moves away, the observer hears a lower frequency.


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