Conditioned air will stop. This air will now be used to run the engine starters. WIDE BODY aircraft have to be pushed off the gate by ground tugs. Flight attendant or a movie safety demonstration of emergency procedures.
Acceleration pushes body back into seat cushion.
Engine power reduced at some airports to meet noise abatement restrictions of the local area. An increase in speed is felt. Airplanes are restricted to 250 knots when below 10,000 feet. Usually the airplane will BANK and TURN to align with its flight path. Having experienced an unexpected turbulence and wind shear conditions, I highly recommend, if not insist, that you wear your SEAT BELT at all times during the flight.