Each second the video camera can capture 30 pictures of any motion
-- falling objects, thrown objects, colliding objects, rotating objects -- anything that is of interest to the physics student.
High speed consumer camcorders are now available at a price that is within the range of the school laboratory. One of the first reports of the use of this technique in a student lab was an article, "Adding Eyes to your Computer," by Robin Blume-Kohout et al at Kenyon College in The Physics Teacher, 35 pp22-26, 1997.
The critical specification of the camera is an (electronic) shutter speed that can be set to override the automatic determination of shutter speed, and a capability of a shutter speed of at least 1/1000 sec. We have found the Canon ZR (shown in the picture at the left) satisfactory; this camera is being phased out and replaced by the Canon Elura or the more powerful Ultura. Several other cameras are also on the market; not all cameras, however, meet their paper specifications. In particular, the Sony consumer cameras have a history of claiming a faster shutter than they actually have.
Other important specifications are: (1) a manual focus override (because frequently the obect passing in front of the camera during the critical time may not be there as the camera is being focussed, and if the camera is allowed to auto-focus, it may focus on a more distant background, and it will not adjust quickly enough as the object passes.) (2) A liquid crystal display monitor, which is almost universally standard nowadays, so that several students can view the preparation of the scene for the camera simultanneously. (3) Digital video is not essential, but the uploading of the film to the computer is easier and of better quality than the traditional analog video. To take full advantage of the digital video requires so-called "firewire" hardware and software in the computer. In any event, Adobe Premiere or similar capture software is needed. Capture is usually done in a master computer, and the captured files made available to students.
The best software refrains from doing the thinking for the student. "Measurement in Motion" from Learning in Motion, 500 Seabright Avenue Suite 105, Santa Cruz, CA 95062, requires the student to program the software with the formulas for calculating velocity, acceleration, momentum, etc., in terms of the primary data that is recorded from the video film. This programming feature gives the student other options, such as averaging over larger intervals than the primary 1/30 second between frames.
"Measurement in Motion" is available for Mac and for PC. For information contact www.learn.motion.com
Another excellent software package, only for PC, is "World in Motion" from Physics Curriculum and Instruction, 22585 Woodhill Drive, Lakeville, MN (612)461-3470.This software does not require the student to instruct the computer how to calculate functions, and this limits the options for the analysis available.
"Videopoint" from Lennox Softwork, 114 Main Street, Lenox, MA 01240 is the most elaborate software, and the various options to have the computer do curve fitting for the student are temptations to get meaningless results whose source is magically produced by often inappropriate algorithms. This software is available for PC and Mac. www.lsw.com/videopoint
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