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ERIC Number: EJ860276
Record Type: Journal
Publication Date: 2008-Oct
Pages: 3
Abstractor: As Provided
Reference Count: 3
ISBN: N/A
ISSN: ISSN-0031-921X
Measurement of "g" Using a Flashing LED
Terzella, T.; Sundermier, J.; Sinacore, J.; Owen, C.; Takai, H.
Physics Teacher, v46 n7 p395-397 Oct 2008
In one of the classic free-fall experiments, a small mass is attached to a strip of paper tape and both are allowed to fall through a spark timer, where sparks are generated at regular time intervals. Students analyze marks (dots) left on the tape by the timer, thereby generating distance-versus-time data, which they analyze to extract the acceleration due to gravity "g" with good results. The apparatus, however, is cumbersome and often frustrating for students. High-tech versions of this experiment are done with an object dropped and followed by a motion sensor connected to a computer. The sensor relies on ultrasonic ranging to record distance and time data, which may then be displayed graphically. Students inspect the graphs to determine the value of "g". Although the results are excellent, the emphasis on the computer's ability to collect and analyze data leaves little analysis for the students to perform. Furthermore, neither technique gives an intuitive display of what is happening. The motivation for our work was to overcome these issues by developing an innovative method for measuring "g". In our version of the experiment, students drop a flashing LED at a known frequency and record its trajectory using long exposure photography with a digital camera. Proper choice of flashing LED timing parameters produces an image that allows for an accurate measurement of "g" and at the same time helps to explain what happens during free fall. The experiment remains high-tech in the sense that students learn to use updated equipment to record data and to carry out the analysis.
American Association of Physics Teachers. One Physics Ellipse, College Park, MD 20740. Tel: 301-209-3300; Fax: 301-209-0845; e-mail: pubs@aapt.org; Web site: http://scitation.aip.org/tpt
Publication Type: Journal Articles; Reports - Descriptive
Education Level: N/A
Audience: N/A
Language: English
Sponsor: N/A
Authoring Institution: N/A