The Letter R as a Fulcrum
By itself the "fulcrum" r sound-- whether used alone or in the form "er " (cf. the letter "r" in the bioenergetic alphabet) -- is, in a tactile and affective sense, "teetertotter" neutral.
Our images of the children's playground apparatus and physical memories of how it works are analogous here to the way the isolated r sound hangs suspended in our intonation and breath, and then, depending on the sounds of the letters that proceed and/or follow it when used in combination with it, the way it can either be pulled back down and in – breath-wise – or pushed out, and thereafter either up or down.
For example, take the sound "grr," which is laden, affectively, with a sense of potential threat; but as yet unfulfilled. Just as the r sound hangs suspended, so the lion, tiger, or bear might attack, but on the other hand might not. This could explain why, subliminally, engaging this sound in fact or fiction (cf. The Hungerrr Games) so often carries with it the idea that, all else being equal, we might just as easily escape an impending attack as not. In fact, the threatened attack may not even be carried out.
In the case of the word "power," however, that usually directionally neutral "er" sound, pushed forward by the preceding "p-ow" sound, is propelled smartly out of one's mouth by the end of the articulation, thereby conveying a subtle but undeniable, subliminal sense that whatever was [tip:threatened= perhaps as retaliation for some past injury or prevention against some perceived future one] has indeed occurred, and that an attack or some other forceful result indeed taken place.