I whirl a ball around me (in outer space) in a horizontal circle by holding onto a string attached to the ball. The rope, therefore, provides the centripetal force (call it T, for tension) for the ball. The equal and opposite force to T (in the sense of Newton's third law) is ...

Question

BlackTom AI · Accepted Answer

Tension T is the force exerted by the rope on the ball; Newton’s third law says the partner force is the force the ball exerts on the rope (equal in magnitude, opposite in direction).

1) Relevant knowledge points and concepts
- Newton’s third law: for every force exerted by object A on object B, there is an equal and opposite force exerted by B on A.  
- Action–reaction pairs act on different objects (they do not cancel each other on the same object).  
- Centrifugal force is a fictitious force that appears only in a rotating (non-inertial) frame; it is not the third-law partner of a real contact force.

2) Step-by-step reasoning
- Identify the force T: the rope exerts an inward (centripetal) tension T on the ball. That is the “action” in this pair.  
- Apply Newton’s third law: the reaction must be a force of the ball on the rope, equal in magnitude to T and directed outward along the rope.  
- That reaction force is what the rope (and ultimately your hand through the rope) feels; it is transmitted along the rope to your hand.

3) Intermediate steps / no numeric calculation
- Action: Rope → Ball = T (inward).  
- Reaction: Ball → Rope = −T (outward).  
- These two forces act on different bodies (ball vs rope), satisfying third-law pairing.

4) Why the correct answer is correct
- Option c, “the force of the ball on the rope,” precisely names the reaction force partner to the rope’s force on the ball. It is equal and opposite to T by Newton’s third law.

5) Why the other options are incorrect
- a (unable to be determined): incorrect because third-law pairing is definite and identifiable.  
- b (the force of the ball on my hand): not the immediate reaction; the ball exerts force on the rope, and the rope transmits that force to your hand—so the ball-on-hand is indirect, not the direct pair.  
- d (centrifugal force on the ball): centrifugal force is a fictitious force in a rotating frame, not the physical reaction to tension.

6) Conclusion
The equal and opposite force to T is the force of the ball on the rope, confirming answer c.

I whirl a ball around me (in outer space) in a horizontal circle by holding onto a string attached to the ball. The rope, therefore, provides the centripetal force (call it T, for tension) for the ball. The equal and opposite force to T (in the sense of Newton's third law) is ...单项选择题

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