Why does light bend when it goes from one medium to another? I know it happens due to "refraction" but it's a observation. Why doesn't light just travel from one medium to another just straight with a change in velocity?
 A: Here's a decent analogy...
Imagine a straight line chain of people holding hands such that each person is holding the hand of two other people.  Now imagine they are all walking forward down a road which has tall grass on either side of it.  
Now imagine the chain of people is not perpendicular to the side of the road, but tilted in a way that if they all keep walking forward, one end of the chain is going to start walking into the tall grass, which is going to slow them down compared to the other people in the chain.  As everyone keeps walking, more people will end up in the grass since that's what they are heading toward eventually.  If you look at the whole chain, the section of the chain of people who have to walk slower through the grass will appear to be "bent" with respect to the people who are still walking on the road.  Eventually, when everyone's in the grass, the line of people will be straight again, but moving in a new direction different from the original.
The walking chain of people is like a single wave cycle out of many cycles of a classical light "wave"
