The pully ratio is defined as the ratio of which of the following?

The pulley ratio is defined as the ratio of the pitch diameter of the driven pulley to the pitch diameter of the driver pulley. This ratio is crucial because it directly influences the operational characteristics of a pulley system, such as speed and torque transmission.

When calculating the pulley ratio using the pitch diameters, it helps in determining how changes in the size of the pulleys affect the speeds of each pulley. For instance, if the driven pulley has a larger pitch diameter compared to the driver pulley, the driven pulley will rotate slower while receiving more torque, effectively allowing for a mechanical advantage. Conversely, if the driver pulley is larger, the driven pulley rotates faster but with lower torque. This foundational principle allows engineers and designers to strategically select pulley sizes for desired performance outcomes in mechanical systems.

The other choices do not accurately represent what the pulley ratio is. While factors like speed, force, and torque are important in the overall context of mechanical systems, they do not define the fundamental ratio that relates specifically to the diameters of the pulleys in a drive system.