Gyroscopic precession causes an applied force to be manifested 90 degrees in which direction?

• A. In the direction opposite rotation
• B. In the direction of rotation
• C. 45 degrees to the right
• D. Parallel to gravity

Answer: (B)

When a spinning rotor is subjected to a torque, its angular momentum tends to change in the direction of that torque. The change in angular momentum is what drives the observable motion, but because L is large and the axis is constrained, the axis doesn’t tilt the way you push it. Instead, the rotor precesses: the axis moves perpendicular to both the spin axis and the applied torque. The relation Ω × L = τ describes this, so the precession direction is determined by the cross product of the rotation and the torque.

In practical terms, that means the effect of the applied force shows up 90 degrees away from the force, and in the same sense as the wheel’s rotation. That is why the precession is described as occurring in the direction of rotation.