Inverse Kinematics

Kinematics is the study of the motion of objects. This is related to but distinguished from dynamics in that kinematics studies only the way in which objects move and not the cause of the objects' motion. In 3D computer graphics, the term kinematics describes how joints can be moved to animate objects and characters. There are two main types of kinematics: forward kinematics and inverse kinematics.

Forward kinematics refers to a situation in which each joint in the chain inherits the motion of its parent joint. So if you have four joints in a chain, when you rotate the root, the three child joints move based on the rotation of the root. When you rotate the second joint, the third and fourth joints inherit the motion of the second (see Figure 5.6).