Final answer:
Football players are advised to keep their feet on the ground while tackling to increase the effectiveness of their hits by maximizing the impulse and force applied, using ground friction, and maintaining balance. Leaping through the air can reduce control and force application, making tackles less effective.
Step-by-step explanation:
When football coaches advise players to keep their feet on the ground to block, hit, and tackle, they refer to the principles of momentum, work, and energy in physics. Momentum, a product of mass and velocity, is conserved in a closed system. A player with feet on the ground can use the friction between the cleats and the field to apply a greater force over a longer period, thereby increasing the impulse (change in momentum) delivered to the opponent. This controlled application of force means more efficient use of energy and doing work effectively.
In contrast, a player who leaps through the air lacks this frictional advantage, decreasing their ability to exert substantial forces. Moreover, being airborne compromises balance and control, leading to reduced effectiveness in the tackle and greater vulnerability to counter-moves.
Concerning a small force imparting the same momentum as a larger one, it is a matter of time. If a small force acts over a longer period, it can deliver the same change in momentum as a larger force applied briefly, according to the equation for impulse (Impulse = Force × Time).