Which of the following is a primary use of a gearbox in machinery?

A gearbox is primarily used in machinery to reduce rotational speed. This function is essential in various applications where high-speed motor output needs to be converted into lower-speed output that can deliver greater torque. By using gears of different sizes, the gearbox changes the input speed, allowing for more controlled and effective operation of the machinery that connects to the output shaft.

For instance, if an electric motor spins at a high speed, a gearbox can lower this speed while increasing the torque, making it suitable for applications such as driving wheels or other mechanisms that require more force to operate effectively. This reduction in speed is crucial for ensuring that machinery operates within safe limits and can handle the load efficiently.

While it is true that gearboxes can also be used to change the direction of motion or even to facilitate certain torque measurements through design, their primary design and function focus on converting high-speed input into manageable, lower-speed, high-torque output.