Trajectory of particles rebounding off plane targets

An experimental rig and procedure is described, which is used to determine the distribution of airborne particles rebounding from a target. The particles used are angular coal particles, screened to 125-150 microns, impinging on commercial stainless steel and aluminum alloy targets at about 140 m/s, and at various incident angles; after impact, the mean particle trajectory is found to be curved. An approximate form of trajectory equation is derived, and fitted to the data points in order to determine the true value of rebound angle for each trajectory. The change in direction of the mean particle path is found to be up to 30 deg, depending on the incident angle. The evidence that trajectories are curved indicates that care must be exercised when using double-flash photographic methods to obtain information.