Beat, Resonance and Doppler Effect - James Sy SL 275 Chapin 击败，共振和多普勒效应-杰姆斯SY SL 275查.pptVIP

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2018-06-24 发布于四川
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Beat, Resonance and Doppler Effect - James Sy SL 275 Chapin 击败，共振和多普勒效应-杰姆斯SY SL 275查.ppt

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Beat, Resonance and Doppler Effect - James Sy SL 275 Chapin 击败，共振和多普勒效应-杰姆斯SY SL 275查

The Doppler Effect An observer of the wave crests behind or away from the direction of motion would identify a lower frequency due to a greater travel distance from the vibration source. This apparent change in frequency is called the DOPPLER EFFECT after Christian Doppler (1803 – 1853) The greater the speed, the greater the Doppler effect The police and weather reporters use the Doppler effect of radar waves to measure the speeds of cars or water in clouds. The Doppler Effect Vibrating in a stationary position produces waves in concentric circles. (because the wave speed is the same in all directions) Astronomy and the Doppler Shift Astronomers can measure the Doppler Shift of a moving object. The radio wave has a known frequency for stationary objects. If target is moving away, waves in the signal will be stretched, and will have a lower frequency. The Doppler shift is called “Red shift” if v 0 (moving away) since the wavelength is getting longer and the frequency shorter “Blue Shift” if v 0 (moving closer) since the wavelength is getting shorter and the frequency higher (recall that blue light is higher in frequency than red) TWO CLIPS ON THE DOPPLER EFFECT Bow Waves When the vibration source is moving at the same speed as the wave front, a bow wave is produced. In aircraft this is called the “sound barrier”. It is not a real barrier, but is where the wave crests build up on each other at the speed of sound. Speedboats and supersonic aircraft travel in front of their bow waves. Shock Waves Shock waves produced by supersonic aircraft are the 3-dimensional version of the V-shaped bow wave produced by boats. On the ground this is noted as a sonic boom. SIMULATIONS FOR DOPPLER EFFECT AND BOW WAVES http://www.astro.ubc.ca/~scharein/a311/Sim/doppler/Doppler.html * * Sound – Beats Superposition leads to beats – variation in loudness Resonance Occurs in fixed media length L Depends on boundary conditions Occurs only for certain freque