Question

every action force has an opposite and equal reaction force. determine which of these are action/reaction pairs
check all that apply.
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 boy pushes on a door and the door swings open.
a soccer player kicks a ball and then another soccer player kicks the same ball.
a cat rubs up against a tree and the tree pushes against the cat.
a student pushes another student standing in a line, and that student falls into the next student.

Explanation:

To determine action - reaction pairs, we use Newton's Third Law, which states that for every action, there is an equal and opposite reaction, and these forces act on two different objects.

1. A girl leans against a wall and the wall pushes on the girl: The girl exerts a force (action) on the wall, and the wall exerts an equal and opposite force (reaction) on the girl. These forces act on different objects (girl and wall), so this is an action - reaction pair.
2. A baseball hits a glove and the glove pushes on the ball: The baseball exerts a force (action) on the glove, and the glove exerts an equal and opposite force (reaction) on the baseball. The forces act on different objects (baseball and glove), so this is an action - reaction pair.
3. A cat rubs up against a tree and the tree pushes against the cat: The cat exerts a force (action) on the tree, and the tree exerts an equal and opposite force (reaction) on the cat. The forces act on different objects (cat and tree), so this is an action - reaction pair.
4. A student pushes another student standing in a line, and that student falls into the next student: The first student's push on the second student is an action, but the second student falling into the third is a result of the second student's motion, not a direct reaction force to the first push (the reaction to the first student's push is the second student pushing back on the first, which is not described here as a push back but as a fall into the next). So this is not an action - reaction pair in the context of Newton's Third Law (the forces here are not equal and opposite in the way the law describes, as the second student's fall is due to inertia and a subsequent contact force, not a direct reaction to the first push).
5. A boy pushes on a door and the door swings open: The boy exerts a force (action) on the door, but the door swinging open is due to the net force on the door (the boy's push and the door's hinges' forces, etc.). The reaction force to the boy's push is the door pushing back on the boy, but this is not described as a push back (just the door swinging), so this is not an action - reaction pair in the sense of equal and opposite forces acting on different objects as the main event here is the door's motion, not the reaction force.
6. A soccer player kicks a ball and then another soccer player kicks the same ball: The first kick is an action on the ball, but the second kick is a separate action by a different object on the ball. There is no reaction force to the first kick described here as a reaction (the reaction to the first kick is the ball pushing back on the first player, not the second player kicking the ball). So this is not an action - reaction pair.

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.