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218 lines
8.7 KiB
HTML
218 lines
8.7 KiB
HTML
<!DOCTYPE html>
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<meta http-equiv="content-type" content="text/html; charset=UTF-8">
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<title>Introduction to Waves</title>
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<article id="content" role="main">
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<!-- #BeginEditable "Body" -->
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<h1 class="center">Introduction to Waves</h1>
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<p class="center"><img src="images/water-ripple.jpg" alt="water ripples" height="218" width="480"></p>
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<p class="center large">A wave is a disturbance that moves through space or matter.</p>
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<div class="example">
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<h3>Examples include water waves, sound and light</h3>
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</div>
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<p>The "disturbance" or "variation" can be a change in pressure, electrical intensity or many other things, but there is always a <b>transfer of energy</b>.</p>
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<p>And waves vary about some central value due to a "restoring" force, such as a <a href="spring.html">spring</a>, magnetic force, surrounding pressure, etc.</p>
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<h2>Longitudinal vs Transverse</h2>
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<p>First, play with this animation:</p>
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<div class="script" style="height: 180px;">
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images/waves.js
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</div>
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<p>Notice how the <b>wave moves</b> but the particles just bounce back and forth (longitudinal) or up and down (transverse), but generally do not go anywhere.</p>
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<div class="def">
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<h3>Longitudinal Waves: The disturbance is in the <b>same direction</b> as the wave.</h3>
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<div class="example">
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<h3>Example: A Spring</h3>
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<p>The wave moves left to right, and the disturbance moves left and right also.</p>
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<p class="center"><img src="images/wave-spring.svg" alt="wave in spring"><br>
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This spring has a longitudinal wave</p></div>
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<div class="example">
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<h3>Example: Sound</h3>
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<p class="center"><img src="images/bark.jpg" alt="dog barks" height="184" width="151"><br>
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Sound waves are longitudinal.</p>
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<p>The air goes between compressed and "rarefied":</p>
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<p class="center"><img src="images/compression-rarefaction.svg" alt="compression and rarefaction" height="108" width="272"></p>
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<p>The air molecules bounce back and forth a bit but don't travel anywhere.</p></div>
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</div>
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<p> </p>
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<div class="def">
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<h3>Transverse Waves: The disturbance is at <b>right angles</b> to the wave's direction.</h3>
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<div class="example">
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<h3>Example: a water wave moves left to right, and the disturbance moves <b>up and down</b></h3>
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<p class="center"><img src="images/waves-lake.jpg" alt="waves lake" height="120" width="436"><br>
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Water waves are Transverse Waves.</p>
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<p><i>Did you know that lake and ocean waves are mostly caused by <b>wind</b> over the surface?</i></p>
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</div>
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</div>
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<h2>Transfer Energy not Matter</h2>
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<p>Waves <b>transfer energy</b>, not matter. The matter might bounce up and down (transverse), or back and forth (longitudinal), but generally does not go anywhere.</p>
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<h2>Shapes</h2>
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<p class="center"><img src="images/wave-simple.svg" alt="wave simple" height="" width=""><br>
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We often show waves as simple "sine waves"</p>
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<p class="center"><img src="images/wave-complex.svg" alt="wave complex" height="" width=""><br>
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But they can be a lot more interesting!</p>
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<p>In fact waves can <b>add to each other</b> in an effect called <b>superposition</b>:</p>
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<p class="center"><img src="images/wave-superposition.svg" alt="wave superposition" height="307" width="333"><br>
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Here two different sine waves add together to make a new wave.<br>
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<i>Try "sin(x)+sin(2x)" at the <a href="../data/function-grapher.html">function grapher</a>.</i></p>
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<h2>Mechanical vs Electrical</h2>
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<h3>Mechanical waves travel <b>through matter</b> only.</h3>
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<p>They can't travel through a vacuum.</p>
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<div class="example">
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<p style="float:right; margin: 0 0 5px 10px;"><img src="images/wave-longitudinal.gif" alt="wave longitudinal" height="61" width="200"></p>
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<h3>Example: <a href="waves-sound.html">Sound Waves</a></h3>
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<p>Air molecules collide with each other, after a collision one bounces back and the next bounces forward, and so on.</p>
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<p>Thus they don't really travel anywhere, but the energy goes forward.</p>
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</div>
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<h3>Electrical waves <b>can</b> travel through a vacuum.</h3>
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<p><a href="waves-radio-microwave.html">Radio and microwaves</a>, <a href="light.html">light</a>, and <a href="x-rays-gamma.html">x-rays</a> are all electrical waves.</p>
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<h2>Wavelength and Amplitude</h2>
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<p>The <b>Wavelength</b> is the length from one peak to the next (or from any point to the next matching point):</p>
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<p class="center"><img src="../algebra/images/wavelength-amplitude.svg" alt="amplitude wavelength" height="153" width="511"></p>
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<p>The <b>Amplitude</b> is the height from the center line to the peak (or to the trough). Or we can measure the height from highest to lowest points and divide that by 2.</p>
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<p style="float:right; margin: 0 0 5px 10px;"><img src="images/frequency-hi-lo.svg" alt="frequency low and high" height="214" width="216"></p>
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<h2>Frequency</h2>
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<p>Frequency is how often something happens per unit of time, usually <b>per second</b>.</p>
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<p>When frequency is per second it is called "Hertz" (Hz).</p>
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<div class="example">
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<h3>Example: 50 Hertz means 50 times per second</h3>
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</div>
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<div style="clear:both"></div>
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<p>Play with Amplitude, Wavelength and Frequency in this animation:</p>
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<div style="clear:both"></div>
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<div class="script" style="height: 380px;">
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../algebra/images/wave-sine.js
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</div>
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<p>In fact the Wave Speed, Wavelength and Frequency are related:</p>
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<p class="large center">Wave Speed = Wavelength × Frequency</p>
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<p class="large center">Frequency = <span class="intbl">
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<em>Wave Speed</em>
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Wavelength</span></p>
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<p class="large center">Wavelength = <span class="intbl">
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<em>Wave Speed</em>
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<strong>Frequency</strong>
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</span></p>
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<div class="example">
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<h3>Example: What is the wave speed when the wavelength is 20 m and the frequency is 3 Hz?</h3>
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<p class="large center">Wave Speed = Wavelength × Frequency</p>
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<p class="large center">Wave Speed = 20 m × 3/s</p>
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<p class="larger center">Wave Speed = 60 m/s</p>
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</div>
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<p> </p>
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<div class="questions">17659, 17663, 17665, 7779, 7783, 7785, 7789, 7791, 7796, 17666</div>
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<div class="related">
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<a href="../algebra/amplitude-period-frequency-phase-shift.html">Amplitude, Period, Phase Shift and Frequency</a>
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<a href="waves-seismic.html">Seismic Waves</a>
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<a href="waves-sound.html">Sound Waves</a>
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<a href="waves-radio-microwave.html">Radio Waves</a>
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<a href="index.html">Physics Index</a>
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</div>
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<div id="copyrt">Copyright © 2021 Rod Pierce</div>
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