Question

every action force has an opposite and equal reaction force. determine which of these are action/reaction pairs. choose three correct answers.

• a student pushes another student standing in a line, and that student falls into the next student.
• a girl leans against a wall and the wall pushes on the girl.
• a boy pushes on a door and the door swings open.
• a baseball hits a glove and the glove pushes on the ball.
• a cat rubs up against a tree and the tree pushes against the cat.
• a soccer player kicks a ball and then another soccer player kicks the same ball.

Explanation:

To identify action - reaction pairs, we use Newton's third law: action and reaction forces act on different objects, are equal in magnitude, opposite in direction, and occur simultaneously.

1. A girl leans against a wall and the wall pushes on the girl: The girl exerts a force on the wall (action), and the wall exerts an equal and opposite force on the girl (reaction). These forces act on different objects (girl and wall) and are a pair.
2. A baseball hits a glove and the glove pushes on the ball: The ball (baseball) exerts a force on the glove (action), and the glove exerts an equal and opposite force on the ball (reaction). The forces act on different objects (ball and glove) and form a pair.
3. A cat rubs up against a tree and the tree pushes against the cat: The cat exerts a force on the tree (action), and the tree exerts an equal and opposite force on the cat (reaction). The forces act on different objects (cat and tree) and are a pair.

The other options:

• In "A student pushes another student standing in a line, and that student falls into the next student", the second student falling into the next is a result of the first push, not a direct action - reaction pair with the initial push (involves multiple interactions and not a simple two - object action - reaction).
• In "A boy pushes on a door and the door swings open", the door swinging open is a result of the force, but there is no clear reaction force described (the door's reaction force on the boy is not emphasized in the description as a pair in the same way as the correct ones).
• In "A soccer player kicks a ball and then another soccer player kicks the same ball", these are two separate actions on the ball, not an action - reaction pair (different forces from different objects at different times, not a mutual action - reaction between two objects).

Answer:

• A girl leans against a wall and the wall pushes on the girl.
• A baseball hits a glove and the glove pushes on the ball.
• A cat rubs up against a tree and the tree pushes against the cat.