The discussion centers on the concept of rigid bodies in classical mechanics, highlighting that a rigid body is an idealization that does not exist in reality due to the finite speed of force propagation through materials. When a torque is applied to a long rod, the far end does not move instantaneously because the forces are transmitted at the speed of sound, which is significantly slower than the speed of light. This leads to inaccuracies in calculations, particularly in molecular dynamics where centrifugal forces can stretch molecules, altering their moment of inertia. The conversation references key texts such as "A History of Strength of Materials" by Timoshenko for further understanding.
PREREQUISITESPhysics students, mechanical engineers, material scientists, and anyone interested in the limitations of classical mechanics and the behavior of materials under stress.
- that is not classical but relativistic physics: wrong forumAndrew Mason said:Well, the reason no force propagation can proceed at infinite speed is because it cannot exceed the speed of light. [..]
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Relativity is part of classical physics.harrylin said:- that is not classical but relativistic physics: wrong forum
I disagree. Infinite force is not what is required for a rigid body. Finite force acting instantaneously over a finite distance is what is required.- it completely misses the point, as already explained: infinite force and energy in a piece of matter is unphysical in classical mechanics.