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# Doppler Effect

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## Xing Yao

on 22 April 2013

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#### Transcript of Doppler Effect

Xingyao Chen The Doppler Effect What is It? The Doppler Effect is the effect a sound or light-emitting object has when it is moving towards or away from you. Everyday Examples of the Doppler Effect When a train's horn changes pitch when it moves towards you and past you
the universe is expanding and galaxies are moving away from each other, so the light emitted from galaxies is shifted toward the red end of the spectrum.
The pitch change of the fire siren when the fire truck drives past you. How It Works Although the Doppler Effect was first discovered for sound waves, it applies to all types of waves.

When an object is in motion, the wavelength of the emmited waves are stretch and pulled when it travels for the object to you. As a result, the received frequency is higher or lower depending on the movement of the object relative to you. Stationary Object The dot in the middle represents the object, and each concentric circle shows one wavelength emitted by it. The waves of the stationary source travel outwards from the source in all directions. The circles would reach the observer at the same frequency, so the observer would perceive its actual waves. Both or either the object and the person can move, causing a shift in the waves emitted by the object. Object Moving Towards You Each consecutive wavelength has a shorter distance to travel as the object moves towards you. You observe the waves at a higher frequency than what was originally produced because the wavelengths are compressed . Objects Moving Away From You Each wave has a longer time to travel from the source to the observer. As the waves travel, its wavelengths are stretched out, resulting in a lower frequency. Light Waves vs. Sound Waves In sound, your experience the Doppler Effect because you can hear the change in the sound pitch. Light is also considered waves. When the source is moving towards you, the color of the object shifts towards the blue end of the spectrum, called blue shift. When it is moving away from you, the color shifts towards the red end of the spectrum, called red shift. This happens because red and blue have the longest and shortest wavelengths in the visible spectrum. Breaking The Sound Barrier Mach 1 >Mach 1 When a source is moving at the speed of sound, the observer in the front cannot hear the object at all because all the waves are bunched up in the from. This creates a wall intense pressure in the front, which is broken when the object reaches supersonic speeds. Once the object is traveling faster than the speed of sound, you cannot hear the object until it passes you. Practical Uses For the Doppler Effect Proving the expansion of the Universe
Police radar to measure speed of a passing car
The Doppler radar used by meteorologist to measure weather events Work Cited http://galileoandeinstein.physics.virginia.edu/more_stuff/flashlets/doppler.htm

http://www.acs.psu.edu/drussell/Demos/doppler/doppler.html

http://science.howstuffworks.com/science-vs-myth/everyday-myths/doppler-effect4.htm

http://www.physicsclassroom.com/class/waves/u10l3d.cfm Cool Simulation http://galileoandeinstein.physics.virginia.edu/more_stuff/flashlets/doppler.htm
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