diff --git a/interface/src/Application.cpp b/interface/src/Application.cpp
index 58b28fcef9..f2663829e4 100644
--- a/interface/src/Application.cpp
+++ b/interface/src/Application.cpp
@@ -441,6 +441,7 @@ void Application::aboutToQuit() {
 }
 
 Application::~Application() {
+    _entities.getTree()->setSimulation(NULL);
     qInstallMessageHandler(NULL);
     
     saveSettings();
@@ -1968,7 +1969,9 @@ void Application::init() {
     _entities.init();
     _entities.setViewFrustum(getViewFrustum());
 
-    _entityCollisionSystem.init(&_entityEditSender, _entities.getTree(), _voxels.getTree(), &_audio, &_avatarManager);
+    EntityTree* entityTree = _entities.getTree();
+    _entityCollisionSystem.init(&_entityEditSender, entityTree, _voxels.getTree(), &_audio, &_avatarManager);
+    entityTree->setSimulation(&_entityCollisionSystem);
 
     // connect the _entityCollisionSystem to our script engine's EntityScriptingInterface
     connect(&_entityCollisionSystem, &EntityCollisionSystem::entityCollisionWithVoxel,
@@ -2319,11 +2322,12 @@ void Application::update(float deltaTime) {
 
     if (!_aboutToQuit) {
         PerformanceTimer perfTimer("entities");
+        // NOTE: the _entities.update() call below will wait for lock 
+        // and will simulate entity motion (the EntityTree has been given an EntitySimulation).  
         _entities.update(); // update the models...
-        {
-            PerformanceTimer perfTimer("collisions");
-            _entityCollisionSystem.update(); // collide the entities...
-        }
+        // The _entityCollisionSystem.updateCollisions() call below merely tries for lock,
+        // and on failure it skips collision detection.
+        _entityCollisionSystem.updateCollisions(); // collide the entities...
     }
 
     {
diff --git a/interface/src/Application.h b/interface/src/Application.h
index c75202d96f..1c49e871e7 100644
--- a/interface/src/Application.h
+++ b/interface/src/Application.h
@@ -31,7 +31,6 @@
 #include <QSystemTrayIcon>
 
 #include <EntityEditPacketSender.h>
-#include <EntityCollisionSystem.h>
 #include <NetworkPacket.h>
 #include <NodeList.h>
 #include <PacketHeaders.h>
@@ -60,6 +59,7 @@
 #include "devices/SixenseManager.h"
 #include "devices/Visage.h"
 #include "devices/DdeFaceTracker.h"
+#include "entities/EntityCollisionSystem.h"
 #include "entities/EntityTreeRenderer.h"
 #include "renderer/AmbientOcclusionEffect.h"
 #include "renderer/DeferredLightingEffect.h"
diff --git a/interface/src/entities/EntityCollisionSystem.cpp b/interface/src/entities/EntityCollisionSystem.cpp
index b080212479..1760d63157 100644
--- a/interface/src/entities/EntityCollisionSystem.cpp
+++ b/interface/src/entities/EntityCollisionSystem.cpp
@@ -16,27 +16,33 @@
 #include <CollisionInfo.h>
 #include <HeadData.h>
 #include <HandData.h>
+#include <PerfStat.h>
 #include <SphereShape.h>
 
-#include "EntityItem.h"
+#include <EntityItem.h>
+#include <EntityEditPacketSender.h>
+#include <EntityTree.h>
+#include <EntityTreeElement.h>
+
 #include "EntityCollisionSystem.h"
-#include "EntityEditPacketSender.h"
-#include "EntityTree.h"
-#include "EntityTreeElement.h"
 
 const int MAX_COLLISIONS_PER_Entity = 16;
 
-EntityCollisionSystem::EntityCollisionSystem(EntityEditPacketSender* packetSender,
-    EntityTree* Entities, VoxelTree* voxels, AbstractAudioInterface* audio,
-    AvatarHashMap* avatars) : _collisions(MAX_COLLISIONS_PER_Entity) {
-    init(packetSender, Entities, voxels, audio, avatars);
+EntityCollisionSystem::EntityCollisionSystem()
+    :   SimpleEntitySimulation(), 
+        _packetSender(NULL),
+        _voxels(NULL),
+        _audio(NULL),
+        _avatars(NULL),
+        _collisions(MAX_COLLISIONS_PER_Entity) {
 }
 
 void EntityCollisionSystem::init(EntityEditPacketSender* packetSender,
-    EntityTree* Entities, VoxelTree* voxels, AbstractAudioInterface* audio,
-    AvatarHashMap* avatars) {
+        EntityTree* entities, VoxelTree* voxels, AbstractAudioInterface* audio,
+        AvatarHashMap* avatars) {
+    assert(entities);
+    setEntityTree(entities);
     _packetSender = packetSender;
-    _entities = Entities;
     _voxels = voxels;
     _audio = audio;
     _avatars = avatars;
@@ -45,14 +51,15 @@ void EntityCollisionSystem::init(EntityEditPacketSender* packetSender,
 EntityCollisionSystem::~EntityCollisionSystem() {
 }
 
-void EntityCollisionSystem::update() {
+void EntityCollisionSystem::updateCollisions() {
+    PerformanceTimer perfTimer("collisions");
+    assert(_entityTree);
     // update all Entities
-    if (_entities->tryLockForRead()) {
-        QList<EntityItem*>& movingEntities = _entities->getMovingEntities();
-        foreach (EntityItem* entity, movingEntities) {
+    if (_entityTree->tryLockForRead()) {
+        foreach (EntityItem* entity, _movingEntities) {
             checkEntity(entity);
         }
-        _entities->unlock();
+        _entityTree->unlock();
     }
 }
 
@@ -127,9 +134,8 @@ void EntityCollisionSystem::updateCollisionWithEntities(EntityItem* entityA) {
     CollisionList collisions(MAX_COLLISIONS_PER_ENTITY);
     bool shapeCollisionsAccurate = false;
     
-    bool shapeCollisions = _entities->findShapeCollisions(&entityA->getCollisionShapeInMeters(), 
+    bool shapeCollisions = _entityTree->findShapeCollisions(&entityA->getCollisionShapeInMeters(), 
                                             collisions, Octree::NoLock, &shapeCollisionsAccurate);
-    
 
     if (shapeCollisions) {
         for(int i = 0; i < collisions.size(); i++) {
@@ -203,7 +209,7 @@ void EntityCollisionSystem::updateCollisionWithEntities(EntityItem* entityA) {
                     propertiesA.setPosition(newPositionA * (float)TREE_SCALE);
                     propertiesA.setLastEdited(now);
 
-                    _entities->updateEntity(idA, propertiesA);
+                    _entityTree->updateEntity(idA, propertiesA);
                     _packetSender->queueEditEntityMessage(PacketTypeEntityAddOrEdit, idA, propertiesA);
                 }            
 
@@ -220,7 +226,7 @@ void EntityCollisionSystem::updateCollisionWithEntities(EntityItem* entityA) {
                     propertiesB.setPosition(newPositionB * (float)TREE_SCALE);
                     propertiesB.setLastEdited(now);
 
-                    _entities->updateEntity(idB, propertiesB);
+                    _entityTree->updateEntity(idB, propertiesB);
                     _packetSender->queueEditEntityMessage(PacketTypeEntityAddOrEdit, idB, propertiesB);
                 }      
             }
@@ -326,6 +332,6 @@ void EntityCollisionSystem::applyHardCollision(EntityItem* entity, const Collisi
     properties.setVelocity(velocity * (float)TREE_SCALE);
     properties.setLastEdited(usecTimestampNow());
 
-    _entities->updateEntity(entityItemID, properties);
+    _entityTree->updateEntity(entityItemID, properties);
     _packetSender->queueEditEntityMessage(PacketTypeEntityAddOrEdit, entityItemID, properties);
 }
diff --git a/interface/src/entities/EntityCollisionSystem.h b/interface/src/entities/EntityCollisionSystem.h
index 4b483122fe..a1eb174756 100644
--- a/interface/src/entities/EntityCollisionSystem.h
+++ b/interface/src/entities/EntityCollisionSystem.h
@@ -20,31 +20,29 @@
 
 #include <AvatarHashMap.h>
 #include <CollisionInfo.h>
-#include <SharedUtil.h>
+#include <EntityItem.h>
 #include <OctreePacketData.h>
+#include <SharedUtil.h>
+#include <SimpleEntitySimulation.h>
 #include <VoxelDetail.h>
 
-#include "EntityItem.h"
-
 class AbstractAudioInterface;
 class AvatarData;
 class EntityEditPacketSender;
 class EntityTree;
 class VoxelTree;
 
-class EntityCollisionSystem : public QObject {
+class EntityCollisionSystem : public QObject, public SimpleEntitySimulation {
 Q_OBJECT
 public:
-    EntityCollisionSystem(EntityEditPacketSender* packetSender = NULL, EntityTree* Entitys = NULL, 
-                                VoxelTree* voxels = NULL, AbstractAudioInterface* audio = NULL, 
-                                AvatarHashMap* avatars = NULL);
+    EntityCollisionSystem();
 
-    void init(EntityEditPacketSender* packetSender, EntityTree* Entitys, VoxelTree* voxels, 
+    void init(EntityEditPacketSender* packetSender, EntityTree* entities, VoxelTree* voxels, 
                                 AbstractAudioInterface* audio = NULL, AvatarHashMap* _avatars = NULL);
                                 
     ~EntityCollisionSystem();
 
-    void update();
+    void updateCollisions();
 
     void checkEntity(EntityItem* Entity);
     void updateCollisionWithVoxels(EntityItem* Entity);
@@ -65,7 +63,6 @@ private:
     void emitGlobalEntityCollisionWithEntity(EntityItem* entityA, EntityItem* entityB, const CollisionInfo& penetration);
 
     EntityEditPacketSender* _packetSender;
-    EntityTree* _entities;
     VoxelTree* _voxels;
     AbstractAudioInterface* _audio;
     AvatarHashMap* _avatars;