Using Price Elasticity of Demand : Should America Tax Soda?

So, I thought to myself - "I want a real life example of how we can apply economics."  Of course, given that economics explains everything, that was a task which proved far too hard.

I've narrowed it down to this:

Write an essay "Explain how price elasticity of demand can be used in deciding how to tax demerit goods"

There is an excellent article here.  Within it are other links, so please be warned: the research part of this homework is going to take you some time.