* Refraction is the bending of light as it passes from one medium to another (like from air to glass). This bending happens because light travels at different speeds in different mediums.
* Glass is denser than air. This means light travels slower through glass than it does through air.
* When light enters the denser medium (glass), it slows down and bends towards the normal (an imaginary line perpendicular to the surface of the glass). When it exits the glass and returns to the air, it speeds up again and bends away from the normal.
This bending of light is what causes things to appear distorted when viewed through glass, like a straw in a glass of water.
