When a plane is flying upside down, a pilot can still pour water from a bottle into a cup due to the effects of relative motion and centripetal force. Inside the aircraft, everything, including the bottle and cup, shares the same frame of reference. During an inverted flight, pilots usually maintain a maneuver that simulates normal gravitational pull through centripetal force. This keeps the water behaving as if it were in a regular gravity environment, allowing the pilot to pour it without diff