FCeng84;
All objects with mass are acted upon by gravity such that they would experience a uniform acceleration in the absence of other forces. The concept of weight comes from the force needed to resist the acceleration that gravity would impart if left unchecked. In order for a mass to remain in an unaccelerated state relative to an earth based reference frame a force must be applied to that mass to oppose gravity. Remove that force and the mass will accelerate toward the earth at approximately 9.8 meters per second^2.
Force is measured between objects. In the case of an airplane and cargo, between the body of the aircraft and its contents. Because both the airplane and the cargo are subject to the same gravity field, the force between the two does not represent gravity. There cannot be any force between the airplane and its cargo without some external force acting on the airplane (and here gravity is not a force). On the ground at rest, the external force comes from the gear. In the air the external force comes from the engines and aerodynamic forces. In the air, the forces felt within an airplane have nothing to do with pitch or roll attitude. They are entirely dependent on thrust and the combination of angle of attack, sideslip angle, control surface positions, dynamic pressure (i.e., airspeed), and Mach number.
and,
The reason that the cabin crew has to push the beverage carts when moving forward during a climb is that the thrust is up, not because of pitch attitude. With thrust set for climb, the force needed to push the carts up the aisle would the same whether climbing at the flight path angle that maintains constant speed (i.e., the normal climb condition), flying level with increasing airspeed, or at some extremely high pitch attitude with airspeed decreasing.
The bottom line is that gravity acts on the airplane and its contents equally so it does not generate forces between the two. In the air, only thrust and aerodynamics generate forces that are sensed by the contents and occupants of the airplane.
I'm missing something here and am prepared to learn if the physics makes sense.
It is true and I agree with you that gravity acts on the airplane and contents equally and that as such gravity is not a "force" per se, except when acting upon something that cannot resist gravity's force with an equal-and-opposite force, (such as a galley trolley on wheels in an airplane in stable, level, non-accelerating flight). Gravity's effects could be measured by strain gauges on the bolts that fasten things to the airframe like engines, seats, gear etc, but nothing moves of course, because it is all fastened together. But not things with wheels for example, which are normally intended to move.
Without massive hydraulic system, the gear can't be raised, not because Nz is so high and remaining so but because the gear weighs a lot, and that is gravity's acceleration rate at work.
So, as an interested student of these things who is by no means an engineer but a mere (ret'd) pilot of these aircraft, I need to ask you what causes an increased effort to push something uphill, (in an airplane or anywhere else there is a gravity field), and further, should such force not also affect anything that is not resisting that same force?
Unless I have missed something about aerodynamic forces, your statement, above, is incorrect, isn't it?