Air Resistance in Box2D

I've seen many questions asking how to implement air resistance (drag) in box2d, and the most common solution is to use body.setLinearDamping.  After just a little bit of research, I discovered that calculating air resistance is not that difficult.  Here is an example in Java using box2d.
Note: this is not a full simulation of aerodynamics, it only affects linear velocity.
After reading the source, check out the algorithm in action in this video.

	float dragForce;
	Vector2 appliedDrag = new Vector2();
	float dragAngle;
	float p, A, Cd, v; // elements of the formula see wikipedia entry for Drag (physics)
	/*
	ρ is the density of the fluid,
	v is the speed of the object relative to the fluid,
	A is the cross-sectional area
	Cd is the drag coefficient – a dimensionless number.
	sample drag co-efficients (http://en.wikipedia.org/wiki/Drag_coefficient)
	cube = 1.05
	sphere = 0.47
	streamlined-body (smooth wing shape) = 0.04
	*/
	// it's not necessary to calculate fluid density as I have, try 1.0 and change it until it looks nice
	p = FLUID_DENSITY_OF_AIR * getAtmosphericDensity(ent.getAltitude()); // density of the fluid
	// we can just leave this, cross-sections are beyond the scope of what we want to simulate
	A = 1.0f;
	// a very sleek object
	Cd = 0.05f;
	v = (float) Math.pow(ent.getSpeed(), 2); // speed squared
	dragForce = 0.5f * p * v * Cd * A;
	// we need the angle of the body's current velocity to know which angle we should set the drag force
	dragAngle = ent.body.getLinearVelocity().angle();
	// create a vector based on our dragForce
	appliedDrag.set(dragForce, 0);
	// align the drag to the same angle as our velocity
	appliedDrag.setAngle(dragAngle);
	// drag should slow down velocity when added to current velocity, so we make it negative
	appliedDrag.scl(-1);
	ent.body.applyForceToCenter(appliedDrag, true);

view raw box2d_air_resistance.java hosted with ❤ by GitHub