Q:

How to explain refraction (and reflection) to kids?

My son of 14 is now in his first course of physics in high school. I just helped him by explaining how to trace a light ray refracting as it passes from air to another medium as he didn't get it right from his teacher. That was OK.
But how do I explain why light refracts without talking about momentum and phase?
Thanks in advance!

A:

To think about it simply, I've found it to be easiest to think about the cause of refraction in terms of the change in speed of light through different materials. Different kinds of materials have different permitivitties, therefore EM radiation will travel at different velocities through each material. Due to this effect, and depending on the incident angle, the light will bend accordingly. 
If it helps, I found this nice little analogy:
"Imagine a marching band as it marches at an oblique angle from a pavement (a fast medium) into mud (a slower medium). The marchers on the side that runs into the mud first will slow down first. This causes the whole band to pivot slightly toward the normal (make a smaller angle from the normal)."

