The follower of which linkage moves in an arc?

The crank rocker linkage is the correct answer because, in this mechanism, the follower moves in a circular arc as the crank rotates. This is primarily because the crank transforms rotary motion into the oscillating motion of the rocker arm. Specifically, the crank is attached to the driving link (the arm that rotates), while the follower is connected to the rocker, which allows the follower to pivot around its pivot point, resulting in a movement that describes an arc.

In contrast, the other linkages do not produce a similar arc of motion for the follower. For example, the double rocker linkage typically has two rockers that move back and forth but not in an arc, while the slider crank mechanism features the follower sliding along a straight path rather than moving in an arc. The four-bar linkage often provides a variety of motions depending on the configuration, but generally does not guarantee that the follower will move in an arc as defined in this context. Understanding this difference is crucial in differentiating between the types of linkages and their corresponding motion paths.