Figure 7: Charging of vibrated hollow glass spheres under microgravity produced in the Bremen drop tower 33.
From: Self-charging of identical grains in the absence of an external field
Gravity is about 10−6 g and pressure = 1 mbar. Spheres have density 0.14 g/cm3 and diameters between 125 and 150 μm (Cospheric LLC, Santa Barbara, CA). (a) Typical time-lapse images showing 200 ms superpositions of video frames taken at 110 frames per second. At time = 0, vibration of the transducer shown is initiated, after which the apparatus is rapidly accelerated by catapult, and by several tens of milliseconds, microgravity is achieved. Gravity is nearly nonexistent, so parabolic trajectories can only be due to electrostatics. (b) Horizontal projections of grayscale of time-lapse images are used to evaluate height of bed of agitated particles. Inset shows enlargement just beyond noisy region associated with irregular large particle flights; intersections with dotted line used to estimate bed heights. (c) Estimates of bed height obtained from intersections shown in panel (b), along with exponential fit. Inset shows second experiment where metal plate is covered by insulating tape.
