According to Newton’s third law of motion, forces always occur in pairs called action and reaction. These forces are equal in magnitude, opposite in direction and act on different bodies.
Action and reaction forces do not cancel each other because they act on different bodies.
Action: Person pushes the ground backward.
Reaction: Ground pushes the person forward.
Action: Swimmer pushes water backward.
Reaction: Water pushes swimmer forward.
Action: Bullet moves forward.
Reaction: Gun moves backward.
Action: Hot gases are expelled backward.
Reaction: Rocket moves forward.
Action: Person jumps forward.
Reaction: Boat moves backward.
Action: Person pushes the wall.
Reaction: Wall pushes the person back.
Action: Book pushes the table downward.
Reaction: Table pushes the book upward.
Q1. Action and reaction forces act on: A) Same body B) Different bodies C) Same direction D) Same surface Answer: B Q2. Action and reaction forces are: A) Unequal and opposite B) Equal and same direction C) Equal and opposite D) Unequal and same direction Answer: C Q3. Why do action and reaction forces not cancel each other? A) They are unequal B) They act on same body C) They act on different bodies D) They act at different times Answer: C Q4. Which of the following is an action–reaction pair? A) Weight and normal on same body B) Push of man on wall and wall on man C) Gravity and friction D) Force and acceleration Answer: B Q5. While walking, the reaction force is applied by: A) Air B) Ground C) Legs D) Gravity Answer: B Q6. Recoil of a gun occurs because: A) Bullet has more mass B) Gun is heavy C) Action–reaction forces D) Inertia of rest Answer: C Q7. Rocket moves forward because: A) Air pushes it B) Gravity pulls it C) Gases push backward D) No force acts Answer: C Q8. Book resting on a table is an example of: A) Balanced force only B) Action–reaction pair C) Inertia of motion D) Momentum conservation Answer: B
For every action, there is an equal and opposite reaction.
MCQs are frequently asked on identification of correct action–reaction pairs.
