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134 lines
5.4 KiB
HTML
134 lines
5.4 KiB
HTML
<!DOCTYPE html>
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<html lang="en"><!-- #BeginTemplate "/Templates/Advanced.dwt" --><!-- DW6 -->
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<title>Doppler Effect Model</title>
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<meta name="description" content="Math explained in easy language, plus puzzles, games, quizzes, videos and worksheets. For K-12 kids, teachers and parents.">
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<script>reSpell=[["meter","metre"],["meters","metres"],["center","centre"]];</script>
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<!-- #BeginEditable "Body" -->
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<h1 class="center">Doppler Effect </h1>The "Doppler Effect" happens when a wave's source is <b>moving</b> in relation to us:
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<ul>
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<li>As the source approaches, the waves arrive at a higher frequency</li>
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<li>As the source moves away, the waves have a lower frequency</li></ul>So a passing siren sounds like <i>"nee-nee-nee-nee ... woooo-woooo"</i>, or a passing race-car sounds like <i>"eeee-yoooo":</i>
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<table style="border: 0; margin:auto;">
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<tbody>
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<tr>
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<td colspan="2"><img src="images/doppler-before.gif" alt="doppler approaching" height="146" width="348"></td>
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<td>Approaching: higher frequency</td>
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</tr>
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<tr>
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<td style="text-align:right;">Leaving: lower frequency </td>
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<td colspan="2"><img src="images/doppler-leave.gif" alt="doppler leaving" height="146" width="347"></td>
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</tr>
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<tr>
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<td> </td>
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<td style="width:100px;"> </td>
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<td> </td>
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</tr>
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</tbody></table>
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<p>This applies to all waves, including light waves and even waves on the sea:</p>
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<ul>
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<li><a href="light.html">Light</a> from stars that are moving away are "red-shifted" (a lower frequency of light) and those that move toward us are "blue-shifted"</li>
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<li>On the sea, a boat can travel in the same direction as the waves to make the up-and-down motion slower.</li></ul>
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<p></p>
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<h2>Press Play!</h2>
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<script src="images/doppler.js"></script>
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<script>dopplerMain();</script>
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<h2>About the Model</h2>
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<p>The source emits waves at a fixed frequency, but the observer receives a <b>higher </b>frequency when the source moves <b>towards </b>them (and lower frequency when the source moves away)</p>
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<p>To make the model "honest" I based the received frequency purely on <b>when a wave crosses the center of the blue circle</b>.</p>
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<h3>Why does the sound change in little steps?</h3>
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<p>Because our model is not perfect! Each new wave, as it arrives, changes the average up or down. We could improve the model by using more data points for a smoother result.</p>
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<h3>Relative motion!</h3>
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<p>The model shows the source moving, but it is really the <b>relative motion</b> between source and observer that is important. Imagine you are in a car passing by a sound source ... you would also notice this effect.</p>
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<h3>Light</h3>
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<p>The same model could also show light getting red-shifted for objects moving further apart, or blue-shifted when getting closer. Note that the source's color does not change, but the observation of its color does</p>
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<p><br></p><br>
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<div class="related">
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<a href="waves-sound.html">Sound</a>
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<a href="electromagnetic-spectrum.html">Electromagnetism</a>
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<a href="index.html">Physics Index</a>
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Copyright © 2020 MathsIsFun.com
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