Q. Pretend a person can walk only at a certain pace no faster, no slower. If you time her uninterrupted walk across a room of known length, you can compute her walking speed. If, however, she stops momentarily along the technique to greet others in the room, the extra time spent in her brief interactions gives an average speed across the room that is less than her walking speed. How is this like light passing throughout glass? In what way is it not? Explain.