Granular materials avalanche when a static angle of repose is exceeded and freeze at a dynamic angle of repose. Such avalanches occur subaerially on steep hillslopes and wind dunes and subaqueously at the lee side of deltas. Until now it has been assumed that the angles of repose are independent of gravitational acceleration. The objective of this work is to experimentally determine whether the angles of repose depend on gravity. In 33 parabolic flights in a well‐controlled research aircraft we recorded avalanching granular materials in rotating drums at effective gravitational accelerations of 0.1, 0.38 and 1.0 times the terrestrial value. The granular materials varied in particle size and rounding and had air or water as interstitial fluid. Materials with angular grains had time‐averaged angles of about 40° and with rounded grains about 25° for all effective gravitational accelerations, except the finest glass beads in air, which was explained by static electricity. For all materials, the static angle of repose increases about 5° with reduced gravity, whereas the dynamic angle decreases with about 10°. Consequently, the avalanche size increases with reduced gravity. The experimental results suggest that relatively low slopes of granular material on Mars may have formed by dry flows without a lubricating fluid. On asteroids even lower slopes are expected. The dependence on gravity of angle of repose may require reanalysis of models for many phenomena involving sediment, also at much lower slope angles.

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This paper presents a novel methodology for measuring the drag latency of touchscreens. Drag latency is a characteristic of touch hardware that can affect key metrics of human performance as typically collected in human-in-the-loop (simulator) experiments. The proposed methodology uses a laser and laser sensor to obtain an external measurement of stylus position that is compared, in time, with the digitally measured touch event data. The drag latency is estimated as the time shift required to align the locations of touch sensor activation with the recorded laser beam crossings. Application of this methodology on two touchscreens from different vendors showed that touchscreen drag latency is in general strongly dependent on the input speed and varies between 28 (fast inputs) and 200 ms (slow inputs) for the tested hardware. Furthermore, while drag-latency characteristics seem to generally follow an exponential decay curve as a function of input speed, the latency was found to differ by a factor 2 at low input speeds between both touchscreens. Using the measurements from our proposed methodology to obtain predictive models of touchscreens' drag-latency dependency on input speed was found to facilitate accurate compensation for the drag latency for three different input tasks (chirp, multi-sine, and step) relevant to human-in-the-loop testing. The results suggest that measuring, and compensating for, touchscreen drag latency is essential for human-in-the-loop experiments, to ensure consistent measures of human performance and to enable replication of measured effects.