回転の運動方程式

Kinematic equations for rotational motion with constant angular acceleration are established similarly to linear kinematics. For a rigid body rotating about a fixed axis, the mathematical framework parallels translational motion analysis. This relationship allows engineers to apply familiar kinematic principles to rotational systems, making complex rigid body motion more tractable and predictable.

The translational velocity of a point on a rotating rigid body is expressed as the vector product of angular velocity and the position vector. This velocity is always tangential to the circular path traced by the point. The magnitude depends on both the angular velocity and the distance from the rotation axis, with the direction perpendicular to the radius at every instant.

A point on a rotating rigid body experiences tangential acceleration, which changes the magnitude of velocity, and normal acceleration, which changes the direction of velocity. The tangential component represents the time rate of change of speed, while the normal component represents the time rate of change of direction. Together, these components fully describe the point's acceleration in circular motion.

The acceleration vector is derived by taking the time derivative of the translational velocity vector equation. The first term in this derivative yields tangential acceleration, while the second term provides the normal acceleration component. This vector formulation captures both the rate of speed change and the rate of direction change simultaneously.

The expression rAsinθ corresponds to the radius of the circular path followed by point A on the rotating rigid body. This radius is the perpendicular distance from the rotation axis to the point, determining the magnitude of the point's circular motion. It directly influences both the translational velocity and acceleration magnitudes.

Translational velocity is determined by taking the time derivatives of the displacement equation for a point on the rigid body. This derivative process yields the instantaneous rate of change of position. The resulting velocity vector is always tangential to the circular path, indicating the direction of motion at any given moment.

Tangential acceleration represents the time rate of change of the velocity's magnitude for a point on a rotating rigid body. It indicates how quickly the point's speed increases or decreases along its circular path. This component is essential for understanding how rotational motion changes when angular acceleration is present.