The word gravitational is playable in Words With Friends™, no blanks required. Because it is longer than 7 letters, you would have to play off an existing word or do it in several moves.
Words With Friends™ Letter Score: 21
Highest Scoring Words With Friends™ Plays In The Letters
Seven Letter Word Alert: (29 words)
aviator, granola, ignitor, intagli, invitro, lairing, orating, ovarian, railing, rattail, ratting, ravioli, rioting, roiling, rotting, tailing, tilting, toiling, travail, trivial, vaginal, vagrant, valiant, variant, variola, vatting, vialing, violing, vitriol