--- a/src/proto2/Physics.hh	Wed Nov 12 13:59:01 2008 +0000
+++ b/src/proto2/Physics.hh	Thu Nov 13 16:00:08 2008 +0000
@@ -6,6 +6,7 @@
 const uint16_t PHYSICS_TICK_MS = 50;
 const uint16_t PHYSICS_WORLD_WIDTH = 800;
 const uint16_t PHYSICS_WORLD_HEIGHT = 600;
+const Vector GRAVITY_FORCE(0,-1); 
 
 class PhysicsWorld {
     protected: