一定の角加速度による回転 - I

Rotational kinematic equations mirror linear motion equations by substituting rotational variables for linear ones. Angular velocity replaces linear velocity, angular acceleration replaces linear acceleration, and angular displacement replaces linear displacement. This parallel structure allows the same mathematical framework to describe both types of motion under constant acceleration.

The first rotational kinematic equation states that angular velocity at any time equals initial angular velocity plus the product of angular acceleration and time: ωz = ω0z + αz·t. This equation is derived by rearranging the definition of constant angular acceleration as the change in angular velocity over time.

Under constant angular acceleration, average angular velocity equals half the sum of initial and final angular velocities. This relationship holds because angular velocity increases linearly with time. This simplified calculation is central to deriving the second rotational kinematic equation relating angular position, velocity, and time.

The second equation describes angular position at any time as the sum of initial angular position, displacement under initial angular velocity, and additional displacement from changing angular velocity. Mathematically, it combines the initial state, constant-velocity motion, and acceleration effects to predict the object's rotational position throughout its motion.

When angular acceleration aligns with the angular velocity vector, angular velocity increases with time. Conversely, when angular acceleration opposes the angular velocity vector, angular velocity decreases. The relative directions determine whether the object's rotational speed increases or decreases, affecting both velocity and angular displacement.

Constant angular acceleration equations simplify analysis of rotating systems like flywheels and machinery. These equations provide a consistent mathematical framework to predict how angular displacement, angular velocity, and time relate under constant acceleration, enabling engineers to design and analyze rotational systems efficiently.

Kinematics of rotational motion is the method of analyzing how rotational quantities—angular displacement, angular velocity, and angular acceleration—relate to each other and to time. Under constant angular acceleration, this approach uses simplified kinematic equations to describe and predict the behavior of rotating objects in physics and engineering applications.