{HEAD ~ The balls} are fired at a massive rigid block, with {TAIL ~ the inbound and outbound velocities} being measured 
{ HEAD ~ The balls } are fired at a massive rigid block , with { TAIL ~ the inbound and outbound velocities } being measured
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH