The impact-induced energy transfer and dissipation in granular targets without any confining walls are studied by microgravity experiments .
A solid projectile impacts into a granular target at low impact speed ( 0.045 \leq v _ { p } \leq 1.6 m s ^ { -1 } ) in a laboratory drop tower .
Granular clusters consisting of soft or hard particles are used as targets .
Porous dust agglomerates and glass beads are used for soft and hard particles , respectively .
The expansion of the granular target cluster is recorded by a high-speed camera .
Using the experimental data , we find that ( i ) a simple energy scaling can explain the energy transfer in both , soft- and hard-particles granular targets , ( ii ) the kinetic impact energy is isotropically transferred to the target from the impact point , and ( iii ) the transferred kinetic energy is 2 - 7 % of the projectile ’ s initial kinetic energy .
The dissipative-diffusion model of energy transfer can quantitatively explain these behaviors .