When the switching means causes {HEAD ~ the motor} to {TAIL ~ spin}, the disks free spin around the motor shaft 
to
When the switching means causes { HEAD ~ the motor } to { TAIL ~ spin } , the disks free spin around the motor shaft
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH