which is an action/reaction force pair? check all that apply.
earth pulls on a book, and the book pushes against a shelf.
a hockey stick hits a puck, and the puck pushes against the stick.
a pencil pushes against a piece of paper, and the paper pushes against the desk
a finger pulls on a rubber band, and the rubber band pushes against the finger
a dog pulls on a leash, and the owner pulls back on the leash

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# Brief Explanations:
To identify action - reaction force pairs, we use Newton's Third Law, which states that for every action, there is an equal and opposite reaction, and the forces act on two different objects.
- For the option "Earth pulls on a book, and the book pushes against a shelf": The force of the Earth pulling the book is a gravitational force. The book pushing against the shelf is a normal force. These two forces do not act on two objects as a result of each other (the reaction to the Earth pulling the book should be the book pulling the Earth, not the book pushing the shelf), so this is not an action - reaction pair.
- For the option "A hockey stick hits a puck, and the puck pushes against the stick": When the hockey stick (object A) exerts a force on the puck (object B), according to Newton's Third Law, the puck (object B) will exert an equal and opposite force on the hockey stick (object A). So this is an action - reaction pair.
- For the option "A pencil pushes against a piece of paper, and the paper pushes against the desk": The pencil pushing the paper and the paper pushing the desk are two separate interactions. The reaction to the pencil pushing the paper should be the paper pushing the pencil, not the paper pushing the desk, so this is not an action - reaction pair.
- For the option "A finger pulls on a rubber band, and the rubber band pushes against the finger": When the finger (object A) pulls the rubber band (object B), the rubber band (object B) will pull the finger (object A) (action - reaction forces are equal and opposite, and here the description of the rubber band "pushing" is a bit of a misnomer, but the interaction is between the finger and the rubber band. However, more accurately, if the finger pulls the rubber band, the rubber band pulls the finger. But in terms of the force pair, this is an interaction between two objects. But let's check the last option too.
- For the option "A dog pulls on a leash, and the owner pulls back on the leash": Here, both the dog and the owner are pulling on the leash. The leash is a single object, and these two forces are acting on the same object (the leash), not on two different objects as required by Newton's Third Law (action - reaction forces act on two different objects). So this is not an action - reaction pair. Wait, actually, when the dog pulls the leash, the leash pulls the dog (action - reaction), and when the owner pulls the leash, the leash pulls the owner (action - reaction). But the forces between the dog and the leash, and the owner and the leash are action - reaction pairs. But the option says "A dog pulls on a leash, and the owner pulls back on the leash" – these two forces are both acting on the leash, so they are not an action - reaction pair. Going back to the "finger and rubber band" option: if the finger pulls the rubber band, the rubber band exerts a force on the finger (tension force). The description says the rubber band "pushes" against the finger, which might be a mistake in wording (it should be pulls), but the interaction is between the finger and the rubber band. However, the "hockey stick and puck" option is a clear example of two objects (stick and puck) exerting forces on each other as a result of their interaction. Also, the "finger and rubber band" option: when the finger pulls the rubber band (action), the rubber band pulls the finger (reaction). The option says the rubber band "pushes" against the finger, which is incorrect in terms of the type of force (it's a tension force, so pull), but the interaction is between two objects. But the "hockey stick - puck" interaction is a more straightforward example of an action - reaction pair (the stick hits the puck, so the stick exerts a force on the puck, and the puck exerts a force on the stick). Also, the "dog and leash" – no, because both forces are on the leash. The "pencil and paper" – the paper pushing the desk is a different interaction. The "Earth and book" – the book pushing the shelf is a different interaction. So the correct options are the one with the hockey stick and puck, and the finger and rubber band? Wait, no, let's re - evaluate. Newton's Third Law: $F_{AB}=-F_{BA}$, where $F_{AB}$ is the force exerted by object A on object B, and $F_{BA}$ is the force exerted by object B on object A.
- Hockey stick (A) and puck (B): $F_{stick - puck}=-F_{puck - stick}$ – this is an action - reaction pair.
- Finger (A) and rubber band (B): If the finger pulls the rubber band ($F_{finger - rubber band}$), the rubber band pulls the finger ($F_{rubber band - finger}=-F_{finger - rubber band}$). The description says the rubber band "pushes" against the finger, which is incorrect (it should be pulls), but the interaction is between two objects. However, the option "A dog pulls on a leash, and the owner pulls back on the leash" – both forces are on the leash, so not action - reaction. The "pencil and paper" – the paper pushing the desk is a different interaction. The "Earth and book" – the book pushing the shelf is a different interaction. So the correct options are the hockey stick - puck and the finger - rubber band? Wait, no, maybe I made a mistake. Let's re - check:
Action - reaction pairs must be forces that two objects exert on each other. So:
1. Hockey stick and puck: Stick exerts force on puck, puck exerts force on stick – action - reaction. Correct.
2. Finger and rubber band: Finger pulls rubber band, rubber band pulls finger (the option says "pushes" but it's a tension force, so the direction is opposite, but the interaction is between two objects). So this is also an action - reaction pair? Wait, the problem says "check all that apply". Let's see the original options again.
Wait, the option "A finger pulls on a rubber band, and the rubber band pushes against the finger" – maybe the wording is a bit off, but the key is that the finger and the rubber band are two objects interacting. When the finger pulls the rubber band, the rubber band exerts a force on the finger (which could be described as a pull, but maybe the question considers it as a push - pull pair). And the hockey stick and puck: when the stick hits the puck, the stick exerts a force on the puck, and the puck exerts a force on the stick. So these two options (the hockey stick - puck and the finger - rubber band) are action - reaction pairs? Wait, no, let's check the dog and leash: the dog pulls the leash, the leash pulls the dog (action - reaction), and the owner pulls the leash, the leash pulls the owner (action - reaction). But the forces between the dog and the owner on the leash are not action - reaction because they are on the same object. So the correct options are:
- B. A hockey stick hits a puck, and the puck pushes against the stick
- D. A finger pulls on a rubber band, and the rubber band pushes against the finger (assuming that the "push" is a misdescription and it's a pull, but the interaction is between two objects)
- E. A dog pulls on a leash, and the owner pulls back on the leash – no, because they are acting on the same object. Wait, I think I made a mistake earlier. Let's use the strict definition: action - reaction forces are equal in magnitude, opposite in direction, and act on two different objects.
- For "Earth pulls on a book, and the book pushes against a shelf": Earth (object 1) and book (object 2); book (object 2) and shelf (object 3). So two different interactions, not a pair.
- "A hockey stick hits a puck": stick (1) and puck (2). Stick exerts force on puck, puck exerts force on stick – action - reaction (two objects, equal and opposite forces). Correct.
- "A pencil pushes against a piece of paper, and the paper pushes against the desk": pencil (1) and paper (2); paper (2) and desk (3). Two interactions, not a pair.
- "A finger pulls on a rubber band, and the rubber band pushes against the finger": finger (1) and rubber band (2). Finger pulls rubber band (force from 1 to 2), rubber band pushes finger (force from 2 to 1) – equal and opposite, two objects. So this is an action - reaction pair (even if the "push" is a misnomer, the forces are between two objects).
- "A dog pulls on a leash, and the owner pulls back on the leash": dog (1) and leash (2); owner (3) and leash (2). The forces on the leash are from dog and owner, acting on the same object (leash), so not an action - reaction pair (action - reaction forces act on two different objects, so the reaction to dog pulling leash is leash pulling dog, and reaction to owner pulling leash is leash pulling owner).

So the correct options are B, D. Wait, but let's check again. The option "A dog pulls on a leash, and the owner pulls back on the leash" – the leash is in the middle. The force of the dog on the leash and the owner on the leash are two forces on the same object, so they are not an action - reaction pair. The action - reaction to the dog pulling the leash is the leash pulling the dog, and the action - reaction to the owner pulling the leash is the leash pulling the owner. So the correct options are B (hockey stick and puck) and D (finger and rubber band) and maybe E? No, E is on the same object. Wait, the option "A dog pulls on a leash, and the owner pulls back on the leash" – if we consider the leash as a massless string, then the force of the dog on the leash and the owner on the leash are equal and opposite, but they are acting on the same object, so they are not action - reaction forces (action - reaction forces act on two different objects). So the correct options are B and D.
# Answer:
B. A hockey stick hits a puck, and the puck pushes against the stick
D. A finger pulls on a rubber band, and the rubber band pushes against the finger
E. A dog pulls on a leash, and the owner pulls back on the leash (Wait, no, I think I was wrong about E. Let's use a better source. The correct action - reaction pairs are those where two objects exert forces on each other. So:

- B: Stick and puck – action - reaction. Correct.
- D: Finger and rubber band – finger pulls rubber band, rubber band pulls finger (the "push" is incorrect, but the interaction is between two objects). Correct.
- E: Dog and leash – dog pulls leash, leash pulls dog (action - reaction); owner pulls leash, leash pulls owner (action - reaction). But the forces between the dog and the owner on the leash are not an action - reaction pair because they are on the same object. So E is not correct. So the correct options are B and D.

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