Rigid Body Dynamics
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For analytical convenience, human body segments are considered as rigid bodies. A rigid body is similar to a system of particles in the sense that it is composed of particles. Therefore most of the equations for a system of particles are usable in the dynamics of a rigid body. The main difference is of course that the rigid body is rigid. There is no migration of mass within a rigid body. As a result, the relative positions among the particles composing a rigid body do not change. This will further simplify the equations obtained from a system of particles.

The main strategy in analyzing the motion of a rigid body is to split the motion into the linear motion of the CM and the angular motion of the body about its CM. This is because all particles composing the body show the same relative angular motion about the CM. In other words, one can describe the motion of the rigid body as a whole rather than those of the particles individually. The physical characteristics of a rigid body can be described by its inertial properties: mass and moment of inertia. For this reason, a major portion of discussion will be dedicated to the inertial properties of the rigid body: moment of inertia & inertia tensor.

The pages included in this section are:

Moment of Inertia
Calculation of the MOI
Inertia Tensor
Principal Axes
Transformation of the Inertia Tensor
Angular Momentum
Kinetic Energy

The rigid body dynamics will serve as the building blocks for a more complex type of motion later: motion of a system of rigid bodies.


Young-Hoo Kwon, 1998-