Why does light slow down in mediums like water?

[A.I.]

I understand that the speed of light in different mediums (like water) is slower than that of light in a vaccume. I've also read about some expiriments done in which light had been slowed down to a quite imaginable speed, like 70 Km/h. What causes light to slow down in such instances? Is it just bouncing around a lot, or do the photons actually change speed? If the photons chance speed, WHY?!

 

[ZapperZ]

You may want to start by reading an entry in the FAQ in the General Physics forum.

Zz.

 

[A.I.]

Ah! Sorry, I'll check that first next time.
Thank you for your help.

 

[Garth]

Nevertheless A.I. welcome to these Forums and keep asking the questions!

Garth