Difference between gravity and wind in simulation So this is more of a conceptual question for simulations.
I have gravity in my simulation that is going to the side: $g=(0,10)$.
I know that gravity is acceleration.
But is wind acceleration (another type of gravity in a different direction) or is it velocity?
Assume that wind and gravity are constant in the simulation.
EDIT: I am using Box2D for the simulation, a physics engine, so I am not actually doing the computations - I am just setting the gravity and letting it run.  But since I want to add wind, should I just modify the gravity or should I have some routine that adds to the velocity of each object?
EDIT 2: Could I basically think of wind as constant gravity to the side?
 A: Wind is not an acceleration, but the drag due to the wind is a force applied to the body.  This results in an acceleration according to Newton's second law.  All the forces or accelerations need to be added as vectors to find the magnitude and direction of the total force or acceleration.
Let $\hat{y}$ be the upward direction and $\hat{x}$ be the rightward direction. Then gravity is a downward acceleration $-g\,\hat{y}$ where $g=10\,m/s^2$.
The drag force on a body is $$\vec{F}_d=C_d A \frac{1}{2}\rho v^2\hat{v}$$ where $A$ is the relevant cross-sectional area, $\rho$ is the density of the air, $v$ is the velocity of the air relative to the body, and $\hat{v}$ is the unit vector in the direction of the relative wind (not necessarily the direction of the wind as seen from the ground).  $C_d$ is the drag coefficient, which is a unitless empirically determined fudge factor which is different for different shapes.  You could just set $C_d=1$ if this is a very rough simulation.
If your wind is blowing to the side with velocity $\vec{v}_{wind}=v_{wind} \hat{x}$, and your body is currently moving with velocity $\vec{v}_{body}=v_x\hat{x}+v_y\hat{y}$, then the relative velocity to use in the drag equation is $\vec{v}_{wind}-\vec{v}_{body}=(v_{wind}-v_x)\hat{x}-v_y\hat{y}$, the magnitude of the relative wind is $v=\sqrt{(v_{wind}-v_x)^2+v_y^2}$, the direction of the relative wind is $\hat{v}=\frac{v_{wind}-v_x}{v}\hat{x}-\frac{v_y}{v}\hat{y}$ and the drag is $\vec{F}_d=C_d A\frac{1}{2}\rho v^2\hat{v}=C_d A\frac{1}{2}\rho \sqrt{(v_{wind}-v_x)^2+v_y^2}((v_{wind}-v_x)\hat{x}-v_y\hat{y})$.
According to Newton's 2nd law, the total force is $\sum \vec{F}=m \vec{a}$.  The force due to the gravitational acceleration is $\vec{F}_g=-mg\hat{y}$.  So doing a vector summation of the gravitational and drag forces, we get $$\sum \vec{F}=\vec{F_g}+\vec{F_d}\\=C_d A\frac{1}{2}\rho \sqrt{(v_{wind}-v_x)^2+v_y^2}(v_{wind}-v_x)\hat{x}+(-mg-C_d A\frac{1}{2} \rho \sqrt{(v_{wind}-v_x)^2+v_y^2}v_y)\hat{y}$$  Then from Newton's 2nd law the total acceleration of the body is $$\vec{a}=C_d A\frac{1}{2}\frac{\rho}{m} \sqrt{(v_{wind}-v_x)^2+v_y^2}(v_{wind}-v_x)\hat{x}+(-g-C_d A\frac{1}{2}\frac{\rho}{m} \sqrt{(v_{wind}-v_x)^2+v_y^2}v_y)\hat{y}$$
Your simulator will then integrate this total acceleration.
