Final answer:
Light refracts when traveling from air into glass due to a change in speed caused by differences in optical density. The process, governed by Snell's Law, results in the bending of light towards the normal line as it enters the denser medium.
Step-by-step explanation:
Light refracts when traveling from air into glass because light waves undergo a change in speed when they pass from one medium to another. This process is known as refraction. Refraction occurs because there is a change in light's propagation speed due to the difference in optical density between air and glass. When light rays propagate from air (less optically dense) into glass (more optically dense), they bend towards the normal line—a line perpendicular to the boundary between the two media. This bending happens according to Snell's Law, which relates the angle of incidence to the angle of refraction, taking into account the refractive indices of the two media.