Yanked out the good old Websters Dictionary and here goes.
""ROLL"", 1. MOVES LIKE A BALL, OR AS IF ON WHEELS. 2. REVOLVE, TURN OVER AND OVER. 3. MOVE ON WHEELS.
""COAST"" 1. MOVE BY GRAVITY OR MOMEMTUM. 2. PERSON OR THING THAT COASTS.
Hope this clears up any confusion. (heh!heh!)