tag:techtv.mit.edu,:Array/184926900 2009-06-01 15:48:40 -0400 MIT Department of Physics Technical Services Group Two or more air carts are connected by springs on an air track. When this system is at resonant frequency, symmetrical patterns called <a href="http://en.wikipedia.org/wiki/Normal_mode">normal modes</a> appear. The normal modes are shown in both undriven and driven cases. In the undriven examples, the normal modes are found by placing the carts at certain distances from each other and then letting them oscillate. In the driven examples they are found by driving the system with a motor, and varying the frequency until the normal mode patterns appear. Both of these methods are shown for systems of two, three, and five coupled carts. 459 tag:techtv.mit.edu,:Array/184885060 2009-06-30 14:12:10 -0400 MIT Department of Physics Technical Services Group A wire frame is dipped in bubble solution and placed in front of a speaker. At certain frequencies, the soap film oscillates in symmetrical patterns called <a href="http://en.wikipedia.org/wiki/Normal_mode">normal modes</a>.<br><br> A light is reflected off the soap film through a lens onto the wall to show these normal modes as the frequency of the function generator is increased. The first set of normal modes occur at frequencies lower than we can hear with our ears, which is why you can't hear the speaker in the video until the frequency is increased. 268