Tech Directions - January 2009 - (Page 15) pretation of a vibrating string that nothing more than an inexpensive When I turned the motor on, the might accompany an article about 3 V to 9 V dc power supply. This fact that the point of attachment was string theory, these photographs powers the motor and makes the off center at the top provided the seemed to hold much more promise string vibrate in a regular fashion at needed movement to make the string than a simple image of a plain string low speeds and, at high speeds, in not only rotate but start to vibrate. with a wave pattern on it. an irregular fashion. (See Photos 3 At some voltages, a nice standing The motor was turning the string through 5.) wave was produced while the string at a rate of something like 5 to 20 Next, I decided to go contrary to gyrated in regular fashion. I lined up the string against a black background and flooded it with light from a 300 W flood lamp. I lined up my camera, a Canon Digital Rebel, so that the image plane was parallel to the string. As the string rotated I made a few exposures using a shutter speed fast enough to catch the vibrating action of the string as a sharp record. The resulting images showed simply a string with a wave in it. Not too Photo 3—String begins Photo 4—Low speed Photo 5—Higher speed exciting I thought. to vibrate. produces regular vibration. produces irregular vibration. In the photorevolutions per second. I had chosen convention and, instead of making graph of the basic setup (Photo 1), an exposure time of 1 second so the a sharp record of the string, I purI shortened the string to make the string had a chance to rotate from posefully chose an exposure time illustration’s proportions fit better on 5 to 20 times during the time the long enough to allow the string to the page. Note in Photo 2 the string shutter was open. With the camera make several rotations during the tied at the top off-center on a disc atset to manual exposure, I used an EI exposure cycle. This revealed the tached to the shaft of the motor. of 100 and adjusted the aperture on rotating string not as a single line in The variable voltage supply is the lens to provide sufficient expospace with a wave in it but rather as sure so that when I examined the a “volume,” something that seemed histogram there seemed to be good to have a 3D quality to it. This was highlight and good shadow detail. (EI a bit more interesting than the plain [exposure index] refers to the senstring picture, but then something sor “speed” set in the camera. The unexpected happened. While adjustlower the EI—and 100 is typically the ing the voltage to the motor, the lowest—the better the quality of the voltage went so high as to cause the resulting image.) rotating string to assume a changing The vibrating string appeared to wave pattern, as the weighted-down have volume in Photo 6 even though string could not keep up with the it was just a single string whirling in speed of the disk powering it. The space. This was because the string string wrapped up onto itself, pulldelivered uneven amounts of expoing the weight upwards and causing sure to the sensor, depending on the string to perform rather erratic whether it was traveling towards or motions in the process. away from it or at a right angle to I continued photographing and Photo 2—The string is attached to it during the rotation cycle. When when these images were displayed the edge of a plastic disc fitted to moving at a right angle, the exposure on the LCD screen of the camera it the motor’s shaft. This helps the was as short as the time it took the became clear that as far as an interstring achieve a vibration pattern. www.techdirections.com COMMUNICATION 15 http://www.techdirections.com
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