What are two different sized circular objects attached together and turning as one called?

The correct term for two different sized circular objects attached together and turning as one is a wheel and axle. This mechanical system consists of a large wheel attached to a smaller axle, and when one of these is turned, it causes the other to turn as well due to their connection.

In mechanics, the wheel and axle arrangement allows for the multiplication of force or speed, making it an essential component in various applications, from vehicles to machinery. The wheel allows for easier motion, while the axle provides stability and support. This combination is fundamental in engineering, serving as a basis for many machines and devices.

While other choices involve circular objects or mechanical parts, they do not accurately describe the specific relationship of two different sized circular objects rotating together as a single unit. For example, gears are toothed wheels that interlock to transfer motion and force but are not specifically about two different sizes turning as one. A rotating disc refers to a single flat circular object in motion rather than two attached components. A circular lever is not a standard mechanical term associated with size distinction in rotation.