explain: "**Summary: Newton's Third Law of Motion** **Main Topics and Concepts:** 1. **Newton's Third Law**: States that forces always come in pairs, with equal magnitude and opposite direction. 2. **Force Pairs**: Action force and reaction force, where the action force is the initial force applied, and the reaction force is the responding force. 3. **Simultaneity**: Action and reaction forces occur at the same time. 4. **Different Objects**: Action and reaction forces act on different objects, not on the same object. **Key Formulas and Procedures:** 1. **Mathematical Expression**: F_A→B = -F_B→A, where F_A→B is the force exerted by object A on object B, and F_B→A is the force exerted by object B on object A. 2. **Force Pairs**: Action force (F_A→B) and reaction force (F_B→A) are equal in magnitude and opposite in direction. **Important Examples and Problems:** 1. **Walking**: Foot pushes backward on the ground (action), and the ground pushes the foot forward with an equal force (reaction). 2. **Rocket Launch**: Rocket expels gas downward (action), and the reaction is the rocket being pushed upward. 3. **Jumping**: Pushing down on the floor with legs (action), and the floor pushes up with equal force (reaction). 4. **Swimming**: Pushing water backward with hands (action), and the water pushes the swimmer forward (reaction). **Learning Objectives:** 1. Understand the concept of force pairs and their equal and opposite nature. 2. Recognize that action and reaction forces occur simultaneously. 3. Identify that action and reaction forces act on different objects. 4. Apply Newton's Third Law to explain motion in various scenarios, such as walking, swimming, and rocket launch. **Step-by-Step Processes:** 1. Identify the action force in a given scenario. 2. Identify the reaction force in the same scenario. 3. Recognize that the action and reaction forces are equal in magnitude and opposite in direction. 4. Apply Newton's Third Law to explain the motion in the scenario. **Why It Matters:** Newton's Third Law is fundamental in mechanics, engineering, and everyday life, explaining interaction between objects and predicting forces in structures and bridges."