Learn how Sound Waves Travel in this educational video from dizzo95.
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Female Speaker: When a source is found moves in relation to a listener the pitch or frequency of the sound changes for example as a locomotive whistle approaches the stationary listener sound waves in front of the train's resort crowded together and follow each other at a higher frequency producing an increasingly higher pitch sound. As a locomotive whistle moves away from the listener the sound waves are drawn out to longer wave length at a lower frequency producing a lower pitch sound. This phenomenon is known as the Doppler Effect and it applies to all types of waves. Move the train toward the listener and the whistle rises in pitch. Move the train away from the listener and the whistle lowers in pitch. Scientist use the Doppler Effect to measure star movement the stars light changes the wavelength does it moves toward or away from earth compare the light spectrum emit from the star that is stationary with respect to earth, to the spectrum of the star that is a approaching in earth this stars like shifts to shorter wave lengths of light in the blue end of the spectrum to the spectrum of the star that is residing from earth the stars lie shift to longer wave lengths of light in the red end of the spectrum. An aircraft speed and motion can be calculated by measuring the Doppler shift in frequency that a radio wave emitted from the point on earth undergoes when it is reflected from a moving aircraft as the aircraft approaches the observation the radio waves have higher frequencies as the aircraft recedes from the observation point on earth the radio waves have a longer frequency.

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