Rigidity is described as

• A. The final adjustment and alignment of an aircraft and its flight control system that provides the proper aerodynamic characteristics.
• B. The characteristic of a gyroscope that prevents its axis from tilting as the Earth rotates.
• C. The wheel principle that a heavily weighted rim spinning rapidly stays fixed in the plane.
• D. The rough, milky, opaque ice formed by the instantaneous freezing of small supercooled water droplets.

Answer: (B)

Rigidity in a gyroscope is the tendency of its spinning axis to maintain its direction in space, resisting tilting as the surrounding frame moves. When a rotor spins rapidly, it has large angular momentum along its axis. Forces that try to tilt the axis don’t just topple it; instead, the gyroscope responds in a way that keeps the axis pointed where it’s already pointing in inertial space. On Earth, the surface beneath you is constantly rotating, so this property becomes noticeable: the axis tends to stay fixed relative to distant stars rather than following the rotating ground. That clear, space-fixed orientation is what is meant by rigidity.

The other description you might hear—an almost fixed plane of a spinning wheel—captures a similar idea in everyday terms, but the precise concept here emphasizes the axis resisting tilt relative to space as the planet turns.