What creates the different gear ratios in an automatic transmission?

The correct answer highlights the importance of the planetary gearset in an automatic transmission, which is crucial for creating different gear ratios. A planetary gearset consists of a sun gear, a planet gear, and a ring gear. By varying which component is held stationary or driven, the transmission can achieve multiple gear ratios without the need for a manual shifting process. This allows for smooth transitions between gears during acceleration and deceleration, optimizing engine performance and fuel efficiency.

In automatic transmissions, changes in speed and torque output are achieved by manipulating the arrangement and engagement of the planetary gearsets, which can easily shift between high and low ratios as needed based on driving conditions. As the vehicle accelerates or encounters varying loads, the transmission can adjust seamlessly, ensuring optimal performance.

Other options do not accurately convey the primary mechanism responsible for creating gear ratios. While planetary hydraulics and bearings are components that support the functioning of transmission systems, they do not themselves create gear ratios. Similarly, while multiple gears may be involved in a transmission system, the specific arrangement and interaction of a planetary gearset are what enable the varied gear ratios that characterize automatic transmissions.