In physics, a **rigid body** is an idealization of a solid body of finite size in which deformation is neglected. In other words, the distance between any two given points of a rigid body remains constant in time regardless of external forces exerted on it. Even though such an object cannot physically exist due to relativity, objects can normally be assumed to be perfectly rigid if they are not moving near the speed of light.

In classical mechanics a rigid body is usually considered as a continuous mass distribution, while in quantum mechanics a rigid body is usually thought of as a collection of point masses. For instance, in quantum mechanics molecules (consisting of the point masses: electrons and nuclei) are often seen as rigid bodies (see classification of molecules as rigid rotors).

Read more about Rigid Body: Kinetics, Geometry, Configuration Space

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### Famous quotes containing the words body and/or rigid:

“Summer, this is our flesh,

The *body* you let mature;

If now while the *body* is fresh

You take it, shall we give

The heart....”

—Allen Tate (1899–1979)

“The loosening, for some people, of *rigid* role definitions for men and women has shown that dads can be great at calming babies—if they take the time and make the effort to learn how. It’s that time and effort that not only teaches the dad how to calm the babies, but also turns him into a parent, just as the time and effort the mother puts into the babies turns her into a parent.”

—Pamela Patrick Novotny (20th century)