negative acceleration

21 LETTERS · STARTS WITH N

negative acceleration is a valid 21-letter word worth 28 points in Scrabble and 35 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS

N1E1G2A1T1I1V4E1A1C3C3E1L1E1R1A1T1I1O1N1

1 + 1 + 2 + 1 + 1 + 1 + 4 + 1 + 0 + 1 + 3 + 3 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 =28 PTS

DOUBLE WORD → 56TRIPLE WORD → 84

MEANING

What does negative acceleration mean?