Select the correct answer.
What is the sum of the forces in an action reaction pair?
A. always less than zero
B. always greater than zero
C. always equal to zero
D. sometimes less than zero
Answer (1)
Action-reaction forces are equal in magnitude and opposite in direction.
Express the relationship as F 1 = − F 2 .
Calculate the sum of the forces: F s u m = F 1 + F 2 = 0 .
The sum of the forces in an action-reaction pair is always zero: 0 .
Explanation
Understanding Action-Reaction Pairs Let's analyze the forces in an action-reaction pair. According to Newton's third law, for every action, there is an equal and opposite reaction. This means that the forces in an action-reaction pair have the same magnitude but act in opposite directions.
Expressing the Relationship Mathematically Let F 1 be the force of action and F 2 be the force of reaction. Since the forces are equal in magnitude and opposite in direction, we can write this relationship as: F 1 = − F 2
Calculating the Sum of the Forces Now, let's find the sum of these forces: F s u m = F 1 + F 2 Substitute F 1 = − F 2 into the equation: F s u m = − F 2 + F 2 = 0
Conclusion Therefore, the sum of the forces in an action-reaction pair is always equal to zero.
Examples
Consider a book resting on a table. The book exerts a downward force (action) on the table due to its weight. The table, in turn, exerts an equal and opposite upward force (reaction) on the book, preventing it from falling through the table. The sum of these forces is zero, which is why the book remains at rest. This concept is crucial in understanding how objects interact and remain in equilibrium.
