Physics · SYSTEMS OF PARTICLES AND ROTATIONAL MOTION

An ideal rigid body is defined as a system of particles in which the distances between all pairs of particles do not change under the influence of forces. Which of the following best describes the real-world validity of this model?

1. No real body can ever be analyzed using the rigid body model because all solid bodies warp and twist appreciably under any force.
2. Real bodies deform under forces, but when deformations are negligible, treating them as rigid bodies is a valid and excellent approximation.
3. The rigid body model applies strictly only to macroscopic steel beams and wheels, but breaks down completely for sub-microscopic systems like molecules.
4. Planets and tops cannot be treated as rigid bodies because their self-gravitational forces cause permanent non-negligible deformation.