Pressure supports the weight above it
Hydrostatic equilibrium gives dp/dz = −ρg. With a constant temperature and an ideal gas, this integrates to an exponentially decreasing pressure, not a uniform-pressure layer against a solid roof. Temperature varies with height, so an actual atmospheric profile has several regimes.
Density belongs in a force equation
Molecules move thermally while gravity changes their potential energy with height. The atmosphere becomes progressively thinner. Density and buoyancy describe parts of its mechanical response, but neither removes gravity from the balance.
Leaving the ground preserves velocity
A vehicle and the nearby air already have eastward motion. Lifting vertically does not reset that velocity to zero. Winds and flight controls can change the motion; rotation effects are acceleration terms in a rotating reference frame, rather than a stationary Earth racing underneath every hovering craft.
Level flight follows a changing local vertical
Constant-height flight follows a curved height surface; “level” is local to the aircraft. On a 6,371 km sphere, a 250 m/s path changes local vertical by v/R, about 0.00225° per second or 0.135° per minute. The corresponding inward acceleration is about 0.0098 m/s². This is a geometric example, not a requirement for pilots to make a separate visible downward control input each second.
An aircraft altimeter responds to pressure. An altimeter setting connects its indication with a sea-level reference; pressure altitude uses the standard setting. Temperature and pressure departures affect true height, so an indicated constant altitude is not an exact surveyed circle. Gravity, lift and aircraft controls determine the trajectory in that local reference frame.