Final answer:
The athletic trainer should first stabilize the player's cervical spine and assess consciousness. Keeping feet on the ground during football plays maximizes force and momentum transfer according to physics principles.
Step-by-step explanation:
If a football player remains supine following a collision during full-contact practice, the athletic trainer's first step in an on-field evaluation should be to stabilize the athlete's cervical spine and determine the athlete's level of consciousness. This precaution is vital to prevent any potential spinal injury from becoming worse. Once the cervical spine is secured, other steps such as assessing breathing, circulation, and further injuries should follow in accordance with established emergency procedures and protocols.
Regarding the professional advice for football players to keep their feet on the ground during block, hit, and tackle maneuvers: from the perspective of momentum, work, and energy, having both feet on the ground typically allows a football player to apply a larger force over a greater time period, thus transferring more momentum effectively. This is because the force exerted by the legs can be maximized when they are pushing against a solid surface like the ground, which is based on the physics principle that for every action there is an equal and opposite reaction.