Also, why can’t you get a suntan through a window?
“Welcome to Physics Interactives! This section of our website features a collection of HTML5 interactive pages that allow a user to explore a physics concept. Some Interactives are simulations that allow a user to manipulate an environment and observe the effect of changes in variables upon the simulation. Other Interactives are skill building exercises in which a user practices a skill that is crucial to learning some aspect of physics. And still other Interactives provide game-like environments that require the user to use a physics concept to meet a challenge. The Interactives are intended to be used by the individual student or learner who is attempting to further understand the concept or by a teacher-led classroom as part of a lesson or homework assignment. Most of the Interactives are accompanied by an activity sheet that suggests ways to use the Interactive.”
Hyperphysics is an extensive resource for many subfields of physics. Topics usually include a brief introduction and thorough description, the basic relevant formulas, and links to related topics.