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The use of reflected SOUND WAVEs for obtaining environmental information. Certain animals, such as the bat and the porpoise, emit pulses of extremely high frequency sound (up to 50 kHz for bats, and up to 170 kHz for porpoises and whales) in narrow, intense streams. The REFLECTION, or ECHO, of these sounds supplies information regarding the nature and location of objects in the environment. When an emission of varying frequency is used, such as with bats, the echoes, travelling varying distances to the ear, are heard as different frequencies in each ear, thus supplying directional information.
The rate of repetition of the CYCLEs of a PERIODIC quantity, such as a SOUND WAVE. Thus, frequency is the inverse of the PERIOD. More generally, frequency can be thought of as the rate of change of PHASE.
The atmosphere exerts pressure on all objects in it. When a vibrating body moves in air, it creates slight disturbances of the AMBIENT atmospheric pressure. The AMPLITUDE of these pressure variations is called the sound pressure variation, whereas the effective pressure variation is 0.707 the maximum value. The oscillating variations in sound pressure (called the WAVEFORM of the sound) PROPAGATE in the form of a SOUND WAVE.
The stage that a particle in vibration has reached in its CYCLE. Particles are in phase when they are at the same stage in the cycle at the same time, and out of phase when they are at opposite stages. Phase is measured by the angle of rotation, in degrees or radians.