okay, this may have to do with science. shampoo has "charges" in it, like soap. soap has lots of charges, so that's whay its used to "attract" dirt away from your hands, dishes, etc. so, the same concept is used in your hair. the shampoo "gathers" the dirt from your hair and is rinsed down the drain.
however, you sound like you need conditioner. if your hair is dry, then it is lacking mouister because the shampoo or other stuff may have taken the softness out of it (harsh chemicals-bleah). so, the conditioner should make it soft again.
good luck with your hair!
science classes, yay!