How is it "julia felt good..."? felt is a verb and good is an adjective; adjectives don't modify verbs--adverbs do.
Adjectives can modify verbs, and only linking verbs. Linking verbs don't express action; instead, they link an adjective (which is called the subject complement) to the subject. The most common linking verb is be<a href="%5Bi%5Dam%5B/i%5D,%20%5Bi%5Dis%5B/i%5D,%20%5Bi%5Dare%5B/i%5D">/i</a>: I am good. Another linking verb is *turn: The chameleon turned green. Obviously "good" and "green" cannot describe their respective verbs since they are not adverbs. But we know that "I" is "good" and "the chameleon" is "green."</p>
<p>Similarly, "well," which is an adverb, describes the action of feeling in the clause "she feels well," which makes no sense because it is not the subject's ability to feel that is good; it is the subject herself that is good. Hence, "she feels good" describes what the subject feels (in emotion); "She feels well" describes how the subject feels (e.g., how good her sense of touch is). Feel can be either a linking verb or an action verb, so its object can be either an adjective or an adverb.</p>
<p>The difference between adjectives and adverbs is tested on the SAT pretty frequently. I am not so sure that this specific topic is tested. It should be a simple concept to grasp, however.</p>