Drag force depends on the density of the air, the air's viscosity and compressibility, the velocity of the apple, the size and shape of the apple and the angle between the apple and the air flow.
Funny enough, since Newton's law is m z̈ = ∑ F, the actual velocity of the apple (ż) depends on the mass of the apple after all.
For the approximate force due to gravity, you have m g where g is the acceleration due to the Earth's gravity on objects close to the surface of the Earth.
In total, m z̈ = C ρ A ż^2/2 - m g where C is the drag coefficient, A is the reference area of the apple and ρ is the density of the (assumed spherical) apple.
Funny enough, since Newton's law is m z̈ = ∑ F, the actual velocity of the apple (ż) depends on the mass of the apple after all.
For the approximate force due to gravity, you have m g where g is the acceleration due to the Earth's gravity on objects close to the surface of the Earth.
In total, m z̈ = C ρ A ż^2/2 - m g where C is the drag coefficient, A is the reference area of the apple and ρ is the density of the (assumed spherical) apple.