Final answer:
The analogy between a person walking and stopping in a room and light traveling through glass highlights how interactions can lead to reduced average speeds. Light's apparent slowdown in glass is due to absorption and re-emission, contrasting with actual stops made by the walker. Time perception can also differ between observers based on relative motion, as illustrated by relativity.
Step-by-step explanation:
The example of a person walking across a room and stopping to greet others is analogous to light passing through glass. Light moves at a constant velocity in a vacuum, but when it enters a medium like glass, it interacts with the atoms and molecules within the material, which slows down the light's average speed in a way similar to the walker's reduced average speed due to pauses. However, unlike the person who stops and interacts, light does not actually pause; it is absorbed and re-emitted by atoms, a process that takes time and gives the appearance of slowing down.
As far as the dissimilarities are concerned, the pedestrian's reduction in average speed is due to actual stops, while light's reduction in average velocity does not involve any cessation of motion; the light is continuously in the process of absorption and re-emission by atoms.
Relativity provides another context where elapsed time can be different depending on the observer. For instance, an astronaut moving at near-light speeds experiences time differently compared to an observer on Earth. However, within the astronaut's frame of reference, all clocks indicate the same passage of time due to zero relative velocity. Motion and the passage of time are relative, not absolute.