Final answer:
Football players are more effective at blocking and tackling with their feet on the ground due to better utilization of momentum, work, and energy, and by making full use of friction with the ground for a more forceful impact. Leaping through the air diminishes these advantages as the player cannot exert force against the ground to maximize impact.
Step-by-step explanation:
Football coaches advise players to keep their feet on the ground when blocking, hitting, or tackling because this strategy utilizes the concepts of momentum, work, and energy effectively. When a player's feet are planted on the ground, they can exert more force through their body, directly into the opposing player, without losing energy to other movements. This is because when their feet are on the ground, they can take advantage of the friction between their shoes and the field, which allows them to apply a larger force before slipping, leading to a more effective transfer of momentum to the opposing player.
If a football player leaps through the air to make a tackle, they cannot take advantage of this friction, and their ability to apply force is decreased until they make contact with the other player or the ground again. Also, the work-energy principle indicates that work is a transfer of energy, and in the context of tackling, the player aims to transfer as much kinetic energy to the opponent as possible to halt their momentum. By staying on the ground and driving through the tackle, the player maximizes the energy transfer.
Moreover, Newton's third law tells us that for every action there is an equal and opposite reaction. When a football player is in the air, they lose the benefit of this reaction force from the ground that helps maximize the force they can exert against the opponent. Thus, a lineman who is blocking can actually 'out-push' the opposition by using his strength and the resistance the ground offers to apply a greater force to his opponent than the opponent can apply in return.