diff --git a/src/dev.js b/src/dev.js
index 65a0bc8..0316640 100644
--- a/src/dev.js
+++ b/src/dev.js
@@ -13,6 +13,7 @@
 //   <script src="js/src/tween/easing.js"></script>
 //   <script src="js/src/tween/tween.js"></script>
 //   <script src="js/src/physics/atoms.js"></script>
+//   <script src="js/src/physics/barnes-hut.js"></script>
 //   <script src="js/src/physics/physics.js"></script>
 //   <script src="js/src/physics/system.js"></script>
 //   <script src="js/src/dev.js"></script>
diff --git a/src/kernel.js b/src/kernel.js
index 2ad7149..ffaa682 100644
--- a/src/kernel.js
+++ b/src/kernel.js
@@ -9,7 +9,7 @@
     var chrome_local_file = window.location.protocol == "file:" &&
                             navigator.userAgent.toLowerCase().indexOf('chrome') > -1;
     var USE_WORKER = (window.Worker !== undefined && !chrome_local_file)    
-
+    
     var _physics = null
     var _tween = null
     var _fpsWindow = [] // for keeping track of the actual frame rate
@@ -36,7 +36,7 @@
         var params = pSystem.parameters()
                 
         if(USE_WORKER){
-          trace('using web workers')
+          trace('arbor.js/web-workers',params)
           _screenInterval = setInterval(that.screenUpdate, params.timeout)
 
           _physics = new Worker(arbor_path()+'physics/worker.js')
@@ -46,8 +46,8 @@
                                 physics:objmerge(params, 
                                                 {timeout:Math.ceil(params.timeout)}) })
         }else{
-          trace("couldn't use web workers, be careful...")
-          _physics = Physics(params.dt, params.stiffness, params.repulsion, params.friction, that.system._updateGeometry)
+          trace('arbor.js/single-threaded',params)
+          _physics = Physics(params.dt, params.stiffness, params.repulsion, params.friction, that.system._updateGeometry, params.integrator)
           that.start()
         }
 
diff --git a/src/physics/physics.js b/src/physics/physics.js
index 38ee34d..6536f65 100644
--- a/src/physics/physics.js
+++ b/src/physics/physics.js
@@ -4,7 +4,7 @@
 // the particle system itself. either run inline or in a worker (see worker.js)
 //
 
-  var Physics = function(dt, stiffness, repulsion, friction, updateFn){
+  var Physics = function(dt, stiffness, repulsion, friction, updateFn, integrator){
     var bhTree = BarnesHutTree() // for computing particle repulsion
     var active = {particles:{}, springs:{}}
     var free = {particles:{}}
@@ -17,6 +17,7 @@
     var SPEED_LIMIT = 1000 // the max particle velocity per tick
     
     var that = {
+      integrator:['verlet','euler'].indexOf(integrator)>=0 ? integrator : 'verlet',
       stiffness:(stiffness!==undefined) ? stiffness : 1000,
       repulsion:(repulsion!==undefined)? repulsion : 600,
       friction:(friction!==undefined)? friction : .3,
@@ -29,14 +30,14 @@
       },
 
       modifyPhysics:function(param){
-        $.each(['stiffness','repulsion','friction','gravity','dt','precision'], function(i, p){
+        $.each(['stiffness','repulsion','friction','gravity','dt','precision', 'integrator'], function(i, p){
           if (param[p]!==undefined){
             if (p=='precision'){
               that.theta = 1-param[p]
               return
             }
             that[p] = param[p]
-             
+
             if (p=='stiffness'){
               var stiff=param[p]
               $.each(active.springs, function(id, spring){
@@ -129,10 +130,20 @@
         return _epoch
       },
 
-
       tick:function(){
         that.tendParticles()
-        that.eulerIntegrator(that.dt)
+        if (that.integrator=='euler'){
+          that.updateForces()
+          that.updateVelocity(that.dt)
+          that.updatePosition(that.dt)
+        }else{
+          // default to verlet
+          that.updateForces();
+          that.cacheForces();           // snapshot f(t)
+          that.updatePosition(that.dt); // update position to x(t + 1)
+          that.updateForces();          // calculate f(t+1)
+          that.updateVelocity(that.dt); // update using f(t) and f(t+1) 
+        }
         that.tock()
       },
 
@@ -168,8 +179,8 @@
       },
       
       
-      // Physics stuff
-      eulerIntegrator:function(dt){
+      // Physics stuff      
+      updateForces:function() {
         if (that.repulsion>0){
           if (that.theta>0) that.applyBarnesHutRepulsion()
           else that.applyBruteForceRepulsion()
@@ -177,10 +188,15 @@
         if (that.stiffness>0) that.applySprings()
         that.applyCenterDrift()
         if (that.gravity) that.applyCenterGravity()
-        that.updateVelocity(dt)
-        that.updatePosition(dt)
       },
-
+      
+      cacheForces:function() {
+        // keep a snapshot of the current forces for the verlet integrator
+        $.each(active.particles, function(id, point) {
+           point._F = point.f;
+        });
+      },
+      
       applyBruteForceRepulsion:function(){
         $.each(active.particles, function(id1, point1){
           $.each(active.particles, function(id2, point2){
@@ -266,6 +282,7 @@
       
       updateVelocity:function(timestep){
         // translate forces to a new velocity for this particle
+        var sum=0, max=0, n = 0;
         $.each(active.particles, function(id, point) {
           if (point.fixed){
              point.v = new Point(0,0)
@@ -273,32 +290,43 @@
              return
           }
 
-          var was = point.v.magnitude()
-          point.v = point.v.add(point.f.multiply(timestep)).multiply(1-that.friction);
+          if (that.integrator=='euler'){
+            point.v = point.v.add(point.f.multiply(timestep)).multiply(1-that.friction);
+          }else{
+            point.v = point.v.add(point.f.add(point._F).multiply(timestep*0.5)).multiply(1-that.friction);
+          }
           point.f.x = point.f.y = 0
 
           var speed = point.v.magnitude()          
           if (speed>SPEED_LIMIT) point.v = point.v.divide(speed*speed)
+
+          var speed = point.v.magnitude();
+          var e = speed*speed
+          sum += e
+          max = Math.max(e,max)
+          n++
         });
+        _energy = {sum:sum, max:max, mean:sum/n, n:n}
+        
       },
 
       updatePosition:function(timestep){
         // translate velocity to a position delta
-        var sum=0, max=0, n = 0;
         var bottomright = null
-        var topleft = null
-
+        var topleft = null        
+        
         $.each(active.particles, function(i, point) {
+
           // move the node to its new position
-          point.p = point.p.add(point.v.multiply(timestep));
+          if (that.integrator=='euler'){
+            point.p = point.p.add(point.v.multiply(timestep));
+          }else{
+            //this should follow the equation
+            //x(t+1) = x(t) + v(t) * timestep + 1/2 * timestep^2 * a(t)
+            var accelPart = point.f.multiply(0.5 * timestep * timestep);
+            point.p = point.p.add(point.v.multiply(timestep)).add(accelPart);
+          }
           
-          // keep stats to report in systemEnergy
-          var speed = point.v.magnitude();
-          var e = speed*speed
-          sum += e
-          max = Math.max(e,max)
-          n++
-
           if (!bottomright){
             bottomright = new Point(point.p.x, point.p.y)
             topleft = new Point(point.p.x, point.p.y)
@@ -309,11 +337,10 @@
           if (pt.x===null || pt.y===null) return
           if (pt.x > bottomright.x) bottomright.x = pt.x;
           if (pt.y > bottomright.y) bottomright.y = pt.y;          
-          if   (pt.x < topleft.x)   topleft.x = pt.x;
-          if   (pt.y < topleft.y)   topleft.y = pt.y;
+          if (pt.x < topleft.x)     topleft.x = pt.x;
+          if (pt.y < topleft.y)     topleft.y = pt.y;
         });
         
-        _energy = {sum:sum, max:max, mean:sum/n, n:n}
         _bounds = {topleft:topleft||new Point(-1,-1), bottomright:bottomright||new Point(1,1)}
       },
 
@@ -333,4 +360,4 @@
       var y = center_pt.y
       var d = r*2
       return new Point(x-r+Math.random()*d, y-r+Math.random()*d)
-  }
+  }
\ No newline at end of file
diff --git a/src/physics/system.js b/src/physics/system.js
index b1b722f..3ce52ee 100644
--- a/src/physics/system.js
+++ b/src/physics/system.js
@@ -4,8 +4,8 @@
 // the main controller object for creating/modifying graphs 
 //
 
-  var ParticleSystem = function(repulsion, stiffness, friction, centerGravity, targetFps, dt, precision){
-  // also callable with ({stiffness:, repulsion:, friction:, timestep:, fps:, dt:, gravity:})
+  var ParticleSystem = function(repulsion, stiffness, friction, centerGravity, targetFps, dt, precision, integrator){
+  // also callable with ({integrator:, stiffness:, repulsion:, friction:, timestep:, fps:, dt:, gravity:})
     
     var _changes=[]
     var _notification=null
@@ -17,8 +17,8 @@
     var _bounds = null
     var _boundsTarget = null
 
-    if (typeof stiffness=='object'){
-      var _p = stiffness
+    if (typeof repulsion=='object'){
+      var _p = repulsion
       friction = _p.friction
       repulsion = _p.repulsion
       targetFps = _p.fps
@@ -26,8 +26,11 @@
       stiffness = _p.stiffness
       centerGravity = _p.gravity
       precision = _p.precision
+      integrator = _p.integrator
     }
 
+    // param validation and defaults
+    if (integrator!='verlet' && integrator!='euler') integrator='verlet'
     friction = isNaN(friction) ? .5 : friction
     repulsion = isNaN(repulsion) ? 1000 : repulsion
     targetFps = isNaN(targetFps) ? 55 : targetFps
@@ -35,8 +38,9 @@
     dt = isNaN(dt) ? 0.02 : dt
     precision = isNaN(precision) ? .6 : precision
     centerGravity = (centerGravity===true)
+
     var _systemTimeout = (targetFps!==undefined) ? 1000/targetFps : 1000/50
-    var _parameters = {repulsion:repulsion, stiffness:stiffness, friction:friction, dt:dt, gravity:centerGravity, precision:precision, timeout:_systemTimeout}
+    var _parameters = {integrator:integrator, repulsion:repulsion, stiffness:stiffness, friction:friction, dt:dt, gravity:centerGravity, precision:precision, timeout:_systemTimeout}
     var _energy
 
     var state = {
@@ -68,10 +72,10 @@
         else that.parameters({timeout:1000/(newFPS||50)})
       },
 
-
       start:function(){
         state.kernel.start()
       },
+
       stop:function(){
         state.kernel.stop()
       },