Paul Wainwright
The “Blackburn pendulum” is a common textbook exercise that is familiar to any student of physics, but as a senior in high school in 1967 I saw it as an artistic tool. I proceeded to make a number of simple time exposure photographs, looking up at a small neon bulb attached to such a pendulum.
For the past 8 years I have used a 3-meter Blackburn pendulum in my barn with an LED, and my camera is a large-format 4 x 5 inch sheet film camera. Working at night in total darkness, the camera looks straight up, and a time exposure is made as the LED traces out the pendulum’s path. Depending on the way the pendulum is suspended, and on the particular path it is started in, the LED “paints” a unique image.
Light painting of an LED attached to a Blackburn pendulum strung to produce orthogonal periods of motion in a 4-to-3 ratio. Musically, this would represent a major fourth interval. Exposure was made looking up in total darkness using a 4 x 5 inch sheet film camera. Total exposure time was 8 min 35 sec. The camera was rotated 90 degrees on a slow turntable. For the last minute, the turntable was stopped and the LED was brightened to reveal the heart. Because the formula for the period of motion of a pendulum contains an angular dependence, the Blackburn pendulum goes in and out of resonance as the amplitudes decrease, and in this case the rotation and exposure times were selected to make the heart shape at the end of the exposure.
Light painting of an LED attached to a Blackburn pendulum strung to produce orthogonal periods of motion in a 4-to-3 ratio. Musically, this would represent a major fourth interval. Exposure was made looking up in total darkness using a 4 x 5 inch sheet film camera. Total exposure time was 10 minutes 48 seconds, during which time the camera was rotated 90 degrees on a very slow turntable. Because the formula for the period of motion of a pendulum contains an angular dependence, the Blackburn pendulum goes in and out of resonance as the amplitudes decrease, resulting in interesting patterns that, to me, are quite beautiful.