Is the rotational KE of a rigid body considered as internal energy?

Thread starter etotheipi
Start date Mar 12, 2020
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Body Energy Internal Internal energy Rigid body Rotational

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The discussion centers on whether the rotational kinetic energy (RKE) of a rigid body should be considered part of its internal energy. Participants argue that while the total kinetic energy of a rigid body includes both translational and rotational components, RKE appears macroscopic and thus should not be classified as internal energy. The conversation touches on the distinction between classical mechanics and relativistic concepts, emphasizing that internal energy typically refers to microscopic contributions, which do not include RKE. The idea that rigid bodies have constant internal energy is also debated, with some suggesting that contributions from inter-particle potential energies exist but remain unchanged due to fixed relative positions. Ultimately, the consensus leans toward treating RKE separately from internal energy in rigid body mechanics.

Mar 14, 2020

Herman Trivilino

Science Advisor

Gold Member

etotheipi said:

I think this is helpful, differentiating between distinct dynamical models. It might be best to leave it as such until I've studied continuum & fluid mechanics, since at the moment it feels like I'm missing too many pieces in the jigsaw puzzle!

I think you are conflating the model with the thing being modeled. You will always be able to find shortcomings of any model because it will have limits of validity. There is no such thing as a perfect model. The issue is whether or not the model is good enough to describe the actual behavior.