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Activity
16. Speed of a balloon rip
Equipment needed:
2 Vivitar 283 flash units
8 AA batteries or 2 SB-4 AC adapters
2 cords to connect flash units to sound triggers
2 flash clamps
High-frequency clock (such as the clip
clock)
Electronic stroboscope
2 piezoelectric sound triggers
Meter stick and protractor
Large balloon, preferably cylindrical
Needle or pin
Note: Before doing this activity, try Problem 2 in Appendix
F for practice. The photograph for that problem will also help
in setting up the experiment.
- The setup for this activity is similar to that of the previous
one. Inflate a large balloon and place sound triggers at both
ends of it. Situate the clock disc above the front edge of the
balloon and as nearly parallel to the film plane of the camera
as possible. (See the photograph in Appendix F.) Place both
flash units next to each other and just to the right out of the
picture. The reason for this placement is so that the shadows
cast by the rips will contrast with the rips themselves. Use the
yellow automatic range, and close the lens aperture one stop
from that indicated by the calculator dial. This corrects for
the fact that the balloon will be illuminated by two flashes of
light.
- Prepare for a photograph and puncture the balloon near the
left end. Make an enlargement of the negative and determine the
speed of the rip according to the method of Problem 2.
(Remember, you will need to know the diameter of the clock
disc.)
Note: If you take photographs with a Polaroid camera, see Appendix
C for suggestions. In determining exposure, remember that in
this experiment each exposure results from two flashes of light.
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