The velocity may be measured by the use of {HEAD ~ light screens}, which measure the time required for {TAIL ~ the ball} to travel a fixed distance 
The velocity may be measured by the use of { HEAD ~ light screens } , which measure the time required for { TAIL ~ the ball } to travel a fixed distance
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH