What is contained inside a gyro?

A gyro, specifically in the context of aviation instruments such as gyroscopic instruments, primarily contains flywheels. These flywheels are crucial for the operation of the gyro because they spin at high speeds, creating stability and resistance to any changes in orientation. This stability is essential for the accurate functioning of gyros, which are used for instruments like the artificial horizon or turn coordinator. The gyroscopic principle leads to the ability of these instruments to maintain a reference point in space, which is vital for navigating and controlling the aircraft during flight.

While motors, weight, and rotors could be components of mechanical systems in various contexts, they do not accurately represent the essential components of a gyro itself. Flywheels are specifically designed to provide angular momentum and serve the intended purpose of maintaining orientation, making them the correct answer in relation to the key function of a gyro in aviation.