This Topic was moved here from Exhibition by PhiLho.
As asked at the start of my JBox2D with BoxWrap2D Tutorial thread, I prefer to keep dialog out of this thread...
But I appreciate your interest.

My tutorials use only the physics = new Physics(this, width, height); constructor, but there is another constructor, with more parameters: Physics(PApplet parent, float screenW, float screenH,
   float gravX, float gravY,
   float screenAABBWidth, float screenAABBHeight,
   float borderBoxWidth, float borderBoxHeight,
   float pixelsPerMeter)
As you can see, you can set there a vector defining the gravity (gravX, gravY) in terms of direction and strength.
The simpler constructor calls this one with some default parameters:
this(
   parent,  //parent PApplet
   screenW, screenH,
   0.0f,-10.0f,  //gravity vector
   2*screenW,2*screenH,  //AABB (px)
   screenW,screenH,  //hard border (px)
   10.0f);  //scaling factor, pixels per meter