Relationship between the impact speed v, radius R, and the Young’s modulus E_p of the particles. The curve was derived from Eqs. (1) to (6), given the detected values U_m = 2.45 mV and T_c = 61 μs. The square highlights the case where E_p = 15 MPa (aerogel), which yields R = 0.98 mm and v = 1.95 m s^-1. The Young’s modulus on a logarithmic scale is shown at the top. See text for details.