The suffixes <ic> and <ical> affect the stress pattern of the words to which they are attached. If necessary, the main stress is attracted to the syllable immediately before the suffix. Here are some examples:
magnet = ˈmæɡnət
maɡnetic = məɡˈnetɪkmoron = ˈmɔːrɒn
moronic = məˈrɒnɪkphotograph = ˈfəʊtəɡrɑːf
photographic = ˌfəʊtəˈɡræfɪk
cylinder = ˈsɪlɪndə
cylindrical = sɪˈlɪndrɪklpsychology = saɪˈkɒlədʒi
psychological = ˌsaɪkəˈlɒdʒɪkl
Notice the vowel quality changes in most of the words the words above.
DWhitecloud comments that there are some nouns ending in <ic> that do not follow this pattern: arithmetic, lunatic (noun or adjective), heretic, for instance, all have stress two syllables before the suffix. It has just occurred to me that politic is also an exception of this sort.