What is the significant difference between pastas? Possible Duplicate:
  Why are there so many different pasta shapes?
  What makes a pasta shape pair with a sauce?  




When getting ingredients for a soup recipe, I couldn't find the type of pasta the recipe called, so I just bought a spiral type pasta. It seemed to work fine in the recipe, but it got me thinking about pasta. Forgive my ignorance, but it seems like most pastas taste the same. 

The only thing that seems to make them unique is there size and shape;


Is there any reason I should use one pasta over another if it is relatively the same size as the type of pasta a recipe calls for? 
Do certain pastas cook better in soups, and others require to be drained from liquid? 


I realize I am asking a bunch of questions, but they are mostly to support expanding answers to my main question: What is the significant difference between pastas?
Pasta as you know is a simple egg and flour mixture.  You can add flavouring to it to give it a different spin or even a colour but at it's root it's just an egg dough.

The different type of shapes are "meant" for different types of sauces in a traditional sense.  I don't want to imply that you MUST use one type of pasta with one type of sauce.  What I'm saying is that a particular style of noodle shape just lends itself better to certain suace types.  I.E. penne, rigatoni, macaroni work really well with a sauce that needs a place to sit and hide so that each mouth full gives you the right amount of sauce to noodle ratio.  Mac &amp; Cheese is a great example of this.  

In a soup or salad the type of pasta you choose is probably going to reflect the need of the guest and how you plan to serve the dish.  

With a soup you want to have a spoon that will carry the right proportions of broth, vegetables, pasta in each bite.  Because of that you select a small pasta shape like orzo.  However, as cooking is all about using what you have on hand, if you don't have orzo but you have fetticini then use that but break it up first so it will work the same way.

Hope that helps.