PHY.5:2 - Problem

A detailed account can obscure the mechanism that determines a response. A convenient coarse account can erase the same mechanism. The relevant distinction depends on the question: a description may preserve a mean displacement while losing its spread, or preserve slow motion while losing an initial torque.

A comparison of isolated time scales also misses how parts interact. A rapidly adjusting part can exert a sustained force. Unresolved molecular motion can produce both drag and continuing fluctuations. A small length can become consequential when the imposed variation approaches that length.

The task is to retain the physical influence required by the intended result, while choosing how much of its underlying process to describe.