> since the premise is that they are the same density as the air, hitting a float stone at Mach N might not be any worse than hitting the air at Mach N. Dive i

> since the premise is that they are the same density as the air, hitting a float stone at Mach N might not be any worse than hitting the air at Mach N. Dive into a swimming pool filled with water. Safe, harmless fun! Dive into a pool filled with solid ice. Ice is 10% less dense, so ten percent more safe and harmless and fun, right? Density is not the most important physical quality here.