rigidbody, forces and collision testing

PhysicsEngine/Physics/Forces/GravityForce.cs

@@ -0,0 +1,12 @@
+using System.Numerics;
+
+namespace PhysicsEngine
+{
+    public static class GravityForce
+    {
+        public static void Apply(Body body, float dt)
+        {
+            body.ApplyForce(Vector2.UnitY * 9.81f * body.Mass);
+        }
+    }
+}