What is the primary function of an idler gear?

The primary function of an idler gear is to reverse motion. An idler gear is typically used in a mechanical system to change the direction of rotation without altering the speed or torque of the output. By inserting this gear into the system, it allows the drive gear's motion to be transferred to another gear in a manner that reverses the output rotation direction. This functionality is crucial in applications where a specific orientation of motion is needed, such as in the design of certain types of mechanical linkages or in machinery that requires a specific rotational direction for effective operation.

The other options do not accurately reflect the idler gear's function. While idler gears may indirectly contribute to other effects within a system, their primary purpose is specifically related to reversing motion.