The bending of light as it passes from one medium to another, like from air to glass or water, is called refraction. It happens because of the change in the speed of light as it travels through different materials.

Here's a more detailed explanation:

1. Light travels at different speeds in different mediums: Light travels fastest in a vacuum (like space). When light enters a denser medium, like glass or water, it slows down. This is because the light interacts with the atoms in the material, causing it to change direction and speed.

2. The angle of incidence and angle of refraction: When light strikes the surface of a medium at an angle, it doesn't just slow down, but it also changes direction. The angle at which the light hits the surface is called the angle of incidence, and the angle at which it bends as it enters the new medium is called the angle of refraction.

3. Snell's Law: The relationship between the angle of incidence, angle of refraction, and the speed of light in each medium is described by Snell's Law. It states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is equal to the ratio of the speeds of light in the two mediums.

Why does this bending happen?

Imagine light as a car driving on a smooth road. Now imagine the car suddenly enters a field with soft sand. The car will slow down and its path will slightly bend due to the change in the surface.

Similarly, when light enters a denser medium, it encounters a denser "environment" with more particles. The light interacts with these particles, causing it to slow down and bend.

Here's a visual summary:

* Air: Less dense, light travels faster

* Glass/Water: Denser, light travels slower

When light travels from air to glass/water, it slows down and bends towards the normal (a line perpendicular to the surface). This is because the speed of light is slower in the denser medium.