Final answer:
The heavier an athlete, the more force is required to throw them off balance due to their greater momentum. Momentum is a product of mass and velocity, and a player with a larger mass has more momentum, making it harder to move. The effect of force depends on both its magnitude and the time it takes to act on an object.
Step-by-step explanation:
The sentence should be completed as follows: The heavier an athlete, the more force it takes to throw them off balance and knock them out of position. This is based on the concept of momentum, which is the product of an object's mass and its velocity (momentum = mass × velocity). In sports such as rugby, a player's momentum is a critical factor. If an athlete is heavier, they have more mass, and if moving with a certain velocity, their momentum will be higher. High momentum means it takes a greater force or a longer time for any opposing force to change the player's velocity, which includes knocking them out of position.
Considering momentum also helps understand why a football player's motion is only minimally affected when they catch a ball. Although the ball might be moving at a high velocity, the player has a much greater mass. Therefore, the changes in the player's momentum are relatively small during the action of catching the ball, due to the much larger mass of the player compared to the ball.
Force interactions are also important in understanding the movement of athletes. When unbalanced forces act on players, such as in a game of tug-of-war, the teams will accelerate in opposite directions if the force of tension in the rope is no longer balanced. Similarly, the force of gravity plays a role in how players move and interact during a game, as it is constantly acting upon them.