Introduction to rigid body
A rigid body is an object that has the same shape and size after being subjected to force and the relative position of the internal points. The absolute rigid body does not actually exist, it is just an ideal model, because any object is deformed more or less after the force is applied. If the degree of deformation is extremely small relative to the geometric size of the object itself, the object is studied. Deformation during exercise can be neglected. Considering many solids as rigid bodies, the results obtained are generally sufficiently accurate in engineering. However, to study stress and strain, deformation must be considered. Since the deformation is always small, the object can be regarded as a rigid body first, and the unknown force added to it can be obtained by theoretical mechanics, and then the deformation mechanics, including material mechanics, elastic mechanics, plastic mechanics, etc. Theory and method for research.
The position of the rigid body in space must be determined according to the spatial position of any point in the rigid body and the position of the rigid body when it is rotated around the point (see the normal motion of the rigid body), so the rigid body has six degrees of freedom in the space.