Projects in High-Speed Photography
Supersonic Snap #1
The image below is cropped from a full-size frame (640 x 480 pixels) captured from videotape. The distance scale drawn on the image was determined from a frame of a meter stick held in the plane of the towel's motion. The image may be printed out for analysis.
Try measuring the distance moved by the tip of towel between the green and yellow images. This will be a curved line. Lay out a string or thread along the path that you think the tip would have taken. Then measure the length of the string. The time interval between images was 0.000402 seconds (accurate to within 0.000002 second). Calculate the average speed (distance ÷ time) and estimate the uncertainty in the result. The uncertainty is due primarily to the distance measurement and the accuracy of the superimposed scale. The uncertainty due to the latter is estimated to be 1%. You'll need to estimate the uncertainty in your own measurement of distance. Does your value of average speed agree with that given on the previous page (to within the uncertainty estimate)?