Herbert/Walz

Chapter 17

Study Guide

  1. Key Terms and Points

Section 17.1

  1. Mechanical Wave: a disturbance in matter that carries energy from one place to another.
  2. Medium: materials through which a wave travels
  3. Crest: the highest point of the wave above the rest position
  4. Trough: the lowest point below the rest position
  5. Transverse Wave: a wave that causes the medium to vibrate at right angles to the direction in which the wave travels
  6. Compression: An are where the particles in a medium are spaced close together
  7. Rarefaction: an area where the particles in a medium are spread out
  8. Longitudinal Wave: a wave in which the vibration of the medium is parallel to the direction the wave travels
  9. Surface Wave: a wave that travels along a surface separating two media

Key Points

A mechanical wave is created when a source of energy causes a vibration to travel thorough a medium

The three main types of mechanical waves are transverse waves, longitudinal waves, and surface waves.

Section 17.2

  1. Periodic Motion: any motion that repeats at regular time intervals
  2. Period: the time required for one cycle, a complete motion that returns to its starting point
  3. Frequency: the number of complete cycles in a given time
  4. Hertz: the unit in which frequency is measured
  5. Wavelength: the distance between a point on one wave and the same point on the next cycle of the wave
  6. Amplitude: the maximum displacement of the medium from a wave’s rest position

Key Points

A wave’s frequency equals the frequency of the vibrating source producing the wave.

Increasing the frequency of a wave decreases its wavelength.

If waves are traveling at a constant speed, then wavelength is inversely proportional to frequency.

The more energy a wave has, the greater is its amplitude.

Section 17.3

  1. Reflection: this occurs when a wave bounces off a surface that it cannot pass through
  2. Refraction: the bending of a wave as it enters a new medium at an angle
  3. Diffraction: the bending of a wave as it moves around an obstacle or passes through a narrow opening
  4. Interference: occurs when two or more waves overlap and combine together
  5. Constructive Interference: occurs when two or more waves combine to produce a wave with a larger displacement
  6. Destructive Interference: occurs when two or more waves combine to produce a wave with smaller displacements.
  7. Standing Wave: a wave that appears to stay in one place-it does not seem to move through the medium
  8. Node: a point on a standing wave that has no displacement from the rest position

Key Points:

Reflection does not change the speed or frequency of a wave, but the wave can be flipped upside down.

When a wave enters a medium at an angle, refraction occurs because one side of the wave moves more slowly than the other side.

A wave diffracts more if its wavelength is large compared to the size of an opening or obstacle

Two types of interference are constructive interference and destructive interference.

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.

Section 17.4

  1. Sound Waves: longitudinal waves-compressions and rarefactions that travel through a medium
  2. Loudness: a physical response to the intensity of sound, modified by physical factors.
  3. Pitch: The frequencies of a sound as you perceive it.
  4. Sonar: a technique for determining the distance to an object under water
  5. Doppler Effect: a change in sound frequency caused by motion of the sound source, motion of the listener, or both.
  6. Resonance: the response of a standing wave to another wave of the same frequency

Key Points

Many behaviors of sound can be explained using a few properties-speed, intensity, loudness, and frequency and pitch.

Ultrasound is used in a variety of applications, including sonar and ultrasound imaging.

As a source of sound approaches, an observer hears a higher frequency. When the sound source moves away, the observer hears a lower frequency.

The outer ear gathers and focuses sound into the middle ear, which receives and amplifies the vibrations. The inner ear uses nerve endings to sense vibrations and send signals to the brain.

Speed of Sound = 343 m/s Distance = Speed x Time Speed of Light = 3.0 x 108 m/s

Speed of Sound in Water = 1500m/s Velocity= Wavelength x Frequency

Doppler Effect

  • The Doppler effect is caused by motion of the observer or the source of the wave.
  • The frequency of sound waves changes as the source of the waves moves toward or away from you.

Example: You can hear the train whistle as the train approaches the crossing. The waves are pushed close together by the moving train. Many waves per second reach your ears. The sound waves appear to have a high frequency. As the train passes you, the sound waves spread out and you hear a low frequency.