They act on objects that may have different masses.
Explanation
According to Newton's Third Law of Motion, action and reaction forces are always equal in magnitude and opposite in direction. However, the resulting motion of the objects involved is determined by Newton's Second Law of Motion, which relates force, mass, and acceleration through the equation $F = ma$.
Detailed Analysis
While the forces acting on the two interacting bodies are identical in magnitude ($F$), they act on different objects which may possess different masses ($m$).
- Newton's Second Law: Acceleration is defined as $a = \frac{F}{m}$. Since $F$ is constant for both bodies (due to the action-reaction pair), the acceleration is inversely proportional to the mass of the object.
- Effect of Mass: If the two objects have different masses, the lighter object will experience a greater acceleration, while the heavier object will experience a smaller acceleration.
- They act in opposite directions.: The opposite direction of forces explains the vector nature of the interaction but does not account for the difference in the magnitude of acceleration.
- They do not act simultaneously.: Action and reaction forces act simultaneously; there is no time lag between them.
- One force is cancelled by friction.: Action and reaction forces act on different bodies, so they cannot cancel each other out. Friction is an external force and not the primary reason for the difference in acceleration in this context.
Key Takeaway: Action and reaction forces are equal in magnitude, but because they act on different bodies, the resulting accelerations differ if the masses of the bodies are different ($a \propto \frac{1}{m}$).