Presentation on theme: "Mechanical Waves and Sound"— Presentation transcript:
1 Mechanical Waves and Sound Chapter 17Mechanical Waves and Sound
2 Chapter 17*Mechanical wave- disturbance in matter that carries energy from one place to another*Medium- material through which a wave travelsA 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.
3 Chapter 17*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*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*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
5 Chapter 17*Surface wave- wave that travels along a surface separating two media
6 Chapter 17*Periodic motion- any motion that repeats at regular time intervals*Period- time required for one cycle*Frequency- number of complete cycles in a given time
7 Chapter 17 *Hertz- cycles per second; frequency measurement A wave’s 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 waveIncreasing the frequency decreases the wavelength.
8 Chapter 17 FORMULA (speed of waves) Speed (v); wavelength (λ); frequency (f)v = λ·fVelocity of Propagation- speed at which a wave front passes through a medium, relative to the speed of light.
9 Chapter 17If 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 positionThe more energy a wave has, the greater is its amplitude.
10 Chapter 17*Reflection- wave bounces off a surface that it cannot pass throughReflection 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 angleWhen 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 openingA 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*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
12 Chapter 17*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*Antinode- point where a crest or trough occurs midway between two nodesA 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 mediumMany 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.
14 Chapter 17*Intensity- rate at which a wave’s energy flows through a given area*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 wave’s frequency.
15 Chapter 17Ultrasound is used in a variety of applications, including sonar and ultrasound imaging.*Sonar- technique for determining the distance to an object under water.*Doppler effect- change in sound frequency caused by motionAs a source of sound approaches, an observer hears a higher frequency. When the sound source moves away, the observer hears a lower frequency.