DOPPLER EFFECT

1-44 The DOPPLER EFFECT is the apparent change in frequency of a source as it moves toward or away from a detector. It can affect the operation of equipment used to detect and measure wave energy. SOUND can be audible to the human ear or it can be outside the hearing range. NOISE AND TONES are the two general groups that broadly classify ALL sounds. PITCH, INTENSITY, AND QUALITY are the three basic characteristics of sound. Pitch describes the frequency of sound. Intensity describes how much energy is transmitted. Quality enables us to distinguish one sound from another. The DENSITY of a MEDIUM, TEMPERATURE, and ATMOSPHERIC PRESSURE affect the velocity of sound. If temperature, density, or pressure increases, the velocity of sound increases and vice versa. ACOUSTICS is the science of sound and relates to the sense of hearing. ECHO is an example of reflection. Sound echoes are used in sonar and depth finders to determine or measure the range of an object or the depth of the ocean bottom. REVERBERATION is the multiple reflections of sound waves. The prolonged roar of thunder is caused by reverberations. With underwater sound equipment, reverberations of nearby objects may interfere with returning echoes from actual targets. INTERFERENCE occurs when two waves move simultaneously through a medium. They can interfere constructively, destructively, or produce a resultant of zero. RESONANCE occurs when an objects vibrates (or resonates) at its natural frequency. When different frequencies are produced inside a cavity, the sound from the cavity sounds louder at its resonant frequency than at all other frequencies. NOISE is any disturbance that distracts from or distorts the quality of sound. A PHOTON is the smallest unit of radiant energy that makes up light waves and radio waves. ANGSTROM ( XQLWV DUH XVHG IRU PHDVXULQJ WKH wavelength of light. One angstrom = 1055 -10 m.