why do my results change?

[Dragonusthei]

why is it that typeing the exact same thing in the exact same search engines some times brings my site up number 1 then later on that day its like number 14 and seems to constantly change......

[Rincewind]

Because the other web sites on that results page (serp) have changed thier page contents so the relative positions of your sites change even though your page remains the same all the time.