WHAT IS STRESS?

Stress, as a sound phenomenon, can be studied from two points of view: production and perception. 

The production of stressed syllables is said to imply a greater muscular energy than the production of unstressed syllables. From the perceptive point of view, stressed syllables are prominent. 

Prominence is the sum of different factors such as loudness, length, pitch and quality. 

There are three possibilities of stress in a word:

a primary stress: characterised by prominence and, basically, by a rise-fall tone; 

a secondary stress, weaker than the primary stress but stronger than that of the unstressed 

syllables (,photo’graphic); 

and unstressed syllables, defined by the absence of any prominence, becoming then the background against the prominent stressed syllables appear. 

Unstressed syllables normally have the short closed vowels /i/ or /u/ and the schwa

Trujillo, F. English Phonetics and Phonology Stress . Lecture conducted from Roach, Peter. 1991. English Phonetics and Phonology. Cambridge: Cambridge University Press., .