diff --git a/src/game-lib-game.js b/src/game-lib-game.js
index e8c5753..1c8a19c 100644
--- a/src/game-lib-game.js
+++ b/src/game-lib-game.js
@@ -12,14 +12,14 @@ GameLib.D3.Game.prototype.addScene = function(
 };
 
 GameLib.D3.Game.prototype.processPhysics = function (
-    timestep
+    dt
 ) {
     for(var s in this.scenes) {
         var scene = this.scenes[s];
 
         for(var w in scene.worlds) {
             var world = scene.worlds[w];
-            world.step(timestep);
+            world.step(dt);
         }
     }
 };
@@ -36,14 +36,15 @@ GameLib.D3.Game.prototype.render = function(
 };
 
 GameLib.D3.Game.prototype.update = function(
-    dt
+    dt,
+    fixedDt
 ) {
     for(var s in this.scenes) {
         var scene = this.scenes[s];
 
         for(var w in scene.worlds) {
             var world = scene.worlds[w];
-            world.step(dt);
+            world.step(fixedDt);
         }
 
         scene.update(dt);