Doppler Effect

This applet is designed to teach about the Doppler effect, the observed change in frequency of light or sound as the source moves, represented here by a bow and arrow, and target. Use the upper bar to control the animation, with the sliders on the left and right controlling the movement of the objects, and the buttons in the center starting or resetting the animation.

As the bow (source) and target (sink) move at different speeds, notice how the the rate at which the bow fires is different from the rate at which the target is hit. This can be seen in the graph panel below the animation, with more helpful information down there. This difference in the frequencies seen at the source and sink is known as the doppler effect. The same effect is seen in light and sound as well.

In sound, the doppler effect is seen as a change in pitch. As one object making sound is moving towards another which listens, the listener will hear a higher pitched sound. As the noisy object moves away, the listener hears a lower pitched sound. In light, the effect is also known as redshift, and is seen as a change in color. As something emitting light moves towards an observer, the light appears more blue. As the emitter moves away, the light appears more red.

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The information shown here is meant to help illustrate the doppler effect. The graph on the top shows circles when the bow fires and arrow, and crosses when the target is hit by an arrow. The graph on the bottom is a zoomed out version of the top graph. The displays below show the frequency of both the bow firing arrows, and the target being hit.

Play with the movement sliders at the top and observe how the frequency of the target being hit changes.Can you make the crosses appear very close together? Can you space them out as much as you can? Is there a delay between changing the movement and seeing an effect? Why would that be?

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