Physics Flashcards: Identify Action Reaction Force Pairs

What this deck covers

This deck focuses on Identify Action Reaction Force Pairs, giving you a quick way to review the definitions, rules, and examples that matter most for Physics.

How to use these flashcards

Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: Which requirement must be true for two forces to be an action-reaction pair: same object or different objects?

Answer: Different objects. Third law pairs always act on two separate objects, never the same one.

Flashcard 2: Which property must be true for an action-reaction pair: same object or different objects?

Answer: Different objects. Action-reaction pairs always involve two separate objects interacting.

Flashcard 3: Identify the reaction force to: A rope pulls a crate forward (tension on crate).

Answer: The crate pulls the rope backward (tension on rope). Tension forces are mutual; the crate pulls back on the rope equally.

Flashcard 4: What is Newton's third law statement used to identify action-reaction force pairs?

Answer: Forces occur in equal-magnitude, opposite-direction pairs on different objects. Newton's third law states every action has an equal and opposite reaction.

Flashcard 5: Identify the reaction force to: A car tire pushes the road backward.

Answer: The road pushes the tire forward. Cars move forward because tires push road backward, road pushes tire forward.

Flashcard 6: Identify the reaction force to: A table exerts a normal force on a book.

Answer: The book exerts a normal force on the table. Normal forces form action-reaction pairs between surfaces in contact.

Flashcard 7: Which option is the action-reaction pair for tension: rope pulls on a crate to the right?

Answer: Crate pulls on the rope to the left. Tension creates equal and opposite forces at each end of the rope.

Flashcard 8: Which pair is an action-reaction pair: weight and normal on a book, or book-on-table and table-on-book?

Answer: Book-on-table and table-on-book. Weight involves Earth; normal involves table. Book-table forces are paired.

Flashcard 9: Which condition must match for an action-reaction pair: same type of interaction or different types?

Answer: Same type of interaction (both contact, or both gravitational, etc.). Pairs must be same interaction type: both contact or both gravitational.

Flashcard 10: Identify the reaction force to: Earth pulls a ball downward by gravity.

Answer: The ball pulls Earth upward by gravity. By Newton's third law, the ball exerts equal gravitational force on Earth.

Flashcard 11: Identify the reaction force to: a bat exerts a force on a baseball during impact.

Answer: The baseball exerts a force on the bat. Contact forces during collision are always mutual between objects.

Flashcard 12: Identify the reaction force to: A rocket pushes exhaust gases downward.

Answer: The exhaust gases push the rocket upward. Rocket propulsion: gases push rocket up as rocket pushes gases down.

Flashcard 13: Identify the reaction force to: A charged rod exerts an electric force on a charged ball.

Answer: The charged ball exerts an electric force on the rod. Electric forces obey Newton's third law; both charges exert equal forces.

Flashcard 14: Identify the reaction force to: A hand pushes a wall to the right.

Answer: The wall pushes the hand to the left. The wall exerts equal force back, preventing the hand from moving through.

Flashcard 15: Identify the reaction force to: A person pushes the ground backward while walking.

Answer: The ground pushes the person forward. Walking involves pushing ground backward; ground pushes person forward.

Flashcard 16: Which statement is correct about action-reaction forces: do they cancel in a free-body diagram?

Answer: No; they act on different objects, so they are not on one free-body diagram. Action-reaction pairs act on different objects, never appear together in FBD.

Flashcard 17: Identify the reaction force to: Earth pulls a falling apple downward (gravity).

Answer: The apple pulls Earth upward (gravity). By Newton's third law, gravitational forces are mutual between objects.

Flashcard 18: Identify whether these two forces are a third-law pair: weight on a book and normal on the book.

Answer: No; both forces act on the book, so they are not a third-law pair. Third law requires different objects; weight and normal both act on book.

Flashcard 19: If $A$ pushes $B$ with $10\,\text{N}$ to the east, what is the reaction force on $A$?

Answer: $10\,\text{N}$ to the west (force of $B$ on $A$). Equal magnitude, opposite direction: $10\,\text{N}$ east becomes $10\,\text{N}$ west.

Flashcard 20: Identify the reaction force to: the ground pushes up on a standing person (normal force).

Answer: The person pushes down on the ground. The normal force from ground has its reaction as person pushing down.

Flashcard 21: Identify the reaction force to: a rocket pushes exhaust gases backward.

Answer: The exhaust gases push the rocket forward. Rocket propulsion relies on action-reaction between rocket and gases.

Flashcard 22: Identify the reaction force to: Air exerts drag backward on a moving cyclist.

Answer: The cyclist exerts a forward force on the air. Air resistance has a reaction: the object pushes air in opposite direction.

Flashcard 23: Identify the reaction force to: the road exerts friction backward on a skidding tire.

Answer: The tire exerts friction forward on the road. During skidding, friction forces form an action-reaction pair.

Flashcard 24: What must be true about the directions of forces in an action-reaction pair?

Answer: They are opposite in direction. Action-reaction pairs point in opposite directions along the same line.

Flashcard 25: Identify the reaction force to: a magnet pulls a paperclip toward the magnet.

Answer: The paperclip pulls the magnet toward the paperclip. Magnetic forces are mutual - both objects pull on each other equally.

Flashcard 26: What must be true about the magnitudes of forces in an action-reaction pair?

Answer: They are equal in magnitude. Newton's third law requires forces in pairs to have identical magnitudes.

Flashcard 27: Identify the reaction force to: a tire pushes backward on the road during acceleration.

Answer: The road pushes forward on the tire. Friction pairs: tire pushes road backward, road pushes tire forward.

Flashcard 28: Find the action-reaction pair: air pushes upward on a parachute (drag force).

Answer: The parachute pushes downward on the air. Air resistance pairs: air pushes parachute up, parachute pushes air down.

Flashcard 29: Identify the reaction force to: a book pushes down on a table.

Answer: The table pushes up on the book. The table responds with an equal upward normal force on the book.

Flashcard 30: Identify the reaction force to: a hand pushes on a wall.

Answer: The wall pushes on the hand. By Newton's third law, the wall exerts an equal force back on the hand.

Flashcard 31: Identify the reaction force to: The ground exerts friction on a shoe forward.

Answer: The shoe exerts friction on the ground backward. Friction forces form action-reaction pairs between surfaces.

Flashcard 32: Identify the reaction force to: A magnet pulls a paperclip toward it.

Answer: The paperclip pulls the magnet toward it. Magnetic forces are mutual; both objects attract each other equally.

Flashcard 33: Identify the reaction force to: a person pulls upward on a rope in a tug system.

Answer: The rope pulls downward on the person. Tension forces in rope create equal and opposite pulls on both ends.

Flashcard 34: If object $A$ exerts force \vec{F}_{A\to B} on $B$, what is the reaction force notation?

Answer: $\vec{F}_{B\to A}$. Subscripts reverse for reaction force: $A$ on $B$ becomes $B$ on $A$.

Flashcard 35: Which statement is correct: action-reaction forces cancel on one object, or act on different objects?

Answer: They act on different objects, so they do not cancel on one object. Third law pairs can't cancel because they act on separate objects.

Flashcard 36: Identify the reaction force to: a hammer exerts a force on a nail.

Answer: The nail exerts a force on the hammer. Impact forces are mutual - the nail pushes back on the hammer.

Flashcard 37: Identify the reaction force to: a swimmer pushes water backward with their hands.

Answer: The water pushes the swimmer forward. By Newton's third law, water exerts equal force forward on swimmer.