Question

Explain qualitatively why the combined point-particle/real system approach fails to correctly predict the change in the thermal energy of a system due to frictional forces.

Answer 1

Friction is a non-conservative force - work done against friction is path dependent. In the presence of friction, some kinetic energy is always transformed to thermal energy, so mechanical energy is not conserved.

Since from here it is concluded that total energy remains conserved but a particular form of energy doesn't remain conserved in the frictional analysis.

Also this is for a multi particle system because friction is arises when there is some collision or contact between the particles.

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