Rigid Body (剛體): an object that does not change in size and shape under applied forces.
Center of Mass (質心): the average position of all the mass in a system; a unique point of an object that the resultant force acts on it.
Moment of Inertia (慣性矩): diagonal elements of inertia tensor; a measure of an object's resistance to rotation.
Parallel-axis Theorem (平行軸定理): a theorem relating the moment of inertia about an axis to the moment of inertia about a parallel axis through the center of mass.
Homogeneous (均勻的): uniform composition throughout.
Physical Pendulum (物理擺): a planar rigid body that oscillates about a fixed axis.
Angular Displacement (角位移): the angle through which an object has rotated.