Question

According to Newton's Third Law of Motion (Law of Action and Reaction), forces always occur in equal and opposite pairs. Which of the following sports movements directly demonstrates this law during execution?

• A. \( \text{A swimmer pushing backward against the water to drive their body forward through the pool.} \)
• B. \( \text{An athlete choosing a heavier shotput ball to slow down its acceleration rate.} \)
• C. \( \text{A sprinter continuing to slide along the track after crossing the finish line.} \)
• D. \( \text{A passenger leaning sideways as a bobsled rounds a sharp corner.} \)

Hint:

To identify a Third Law example on the exam, look for movements that involve pushing against a surface or medium (like jumping off the ground, rowing a boat, or swimming) to generate a forward reaction force.

Answer 1

The Correct Option is A

Concept: Biomechanics applies Newton's laws of motion to analyze athletic performance:

• First Law (Inertia): Objects resist changes to their current state of motion.
• Second Law (\( F=ma \)): Acceleration is proportional to force and inversely proportional to mass.
• Third Law (Action/Reaction): For every action force, there is an equal and opposite reaction force.

Step 1: Identify the action and reaction forces in the swimming movement.
When a swimmer performs a stroke, their hands and feet exert a backward force on the water (Action). According to Newton's third law, the water exerts an equal and opposite force forward on the swimmer's body (Reaction), driving them forward through the pool.

Step 2: Identify the mechanical laws behind the other options.

• The shotput example describes the relationship between force, mass, and acceleration governed by the Second Law.
• The sprinter sliding past the finish line demonstrates the property of inertia described by the First Law.