diff --git a/sources/reactphysics3d/engine/CollisionWorld.cpp b/sources/reactphysics3d/engine/CollisionWorld.cpp
index f6d917e6..eddcd5f9 100644
--- a/sources/reactphysics3d/engine/CollisionWorld.cpp
+++ b/sources/reactphysics3d/engine/CollisionWorld.cpp
@@ -19,6 +19,7 @@
 
 // Libraries
 #include "CollisionWorld.h"
+#include "../constraint/Contact.h"
 
 // We want to use the ReactPhysics3D namespace
 using namespace reactphysics3d;
@@ -31,7 +32,10 @@ CollisionWorld::CollisionWorld(const Vector3D& gravity)
 
 // Destructor
 CollisionWorld::~CollisionWorld() {
-
+    // Delete all the constraint
+    for (std::vector<Constraint*>::iterator it = constraintList.begin(); it != constraintList.end(); ) {
+        delete (*it);
+    }
 }
 
 // Add a constraint
@@ -43,3 +47,23 @@ void CollisionWorld::addConstraint(Constraint* constraint) throw(std::invalid_ar
 void CollisionWorld::removeConstraint(Constraint* constraint) throw(std::invalid_argument) {
     // TODO : Implement this method
 }
+
+ // Remove all collision contacts constraints
+void CollisionWorld::removeAllContactConstraints() {
+    // For all constraints
+    for (std::vector<Constraint*>::iterator it = constraintList.begin(); it != constraintList.end(); ) {
+
+        // Try a downcasting
+        Contact* contact = dynamic_cast<Contact*>(*it);
+
+        // If the constraint is a contact
+        if (contact != 0) {
+            // Delete the  contact
+            delete (*it);
+            it = constraintList.erase(it);
+        }
+        else {
+            ++it;
+        }
+    }
+}
diff --git a/sources/reactphysics3d/engine/CollisionWorld.h b/sources/reactphysics3d/engine/CollisionWorld.h
index 7e4dc4e5..fce56dd2 100644
--- a/sources/reactphysics3d/engine/CollisionWorld.h
+++ b/sources/reactphysics3d/engine/CollisionWorld.h
@@ -47,6 +47,7 @@ class CollisionWorld : public DynamicWorld {
 
         void addConstraint(Constraint* constraint) throw(std::invalid_argument);            // Add a constraint
         void removeConstraint(Constraint* constraint) throw(std::invalid_argument);         // Remove a constraint
+        void removeAllContactConstraints();                                                 // Remove all collision contacts constraints
         std::vector<Constraint*>::const_iterator getConstraintListStartIterator() const;    // Return a start iterator on the constraint list
         std::vector<Constraint*>::const_iterator getConstraintListEndIterator() const;      // Return a end iterator on the constraint list
 };
diff --git a/sources/reactphysics3d/engine/DynamicEngine.cpp b/sources/reactphysics3d/engine/DynamicEngine.cpp
index 16848350..e829c6a4 100644
--- a/sources/reactphysics3d/engine/DynamicEngine.cpp
+++ b/sources/reactphysics3d/engine/DynamicEngine.cpp
@@ -51,7 +51,7 @@ DynamicEngine::~DynamicEngine() {
 }
 
 // Update the state of a rigid body
-void DynamicEngine::updateBodyState(RigidBody* const rigidBody) {
+void DynamicEngine::updateBodyState(RigidBody* const rigidBody, const Time& timeStep) {
 
     // If the gravity force is on
     if(world->getIsGravityOn()) {
@@ -63,12 +63,15 @@ void DynamicEngine::updateBodyState(RigidBody* const rigidBody) {
     rigidBody->updatePreviousBodyState();
 
     // Integrate the current body state at time t to get the next state at time t + dt
-    integrationAlgorithm->integrate(rigidBody->getCurrentBodyState(), timer.getTime(), timer.getTimeStep());
+    integrationAlgorithm->integrate(rigidBody->getCurrentBodyState(), timer.getTime(), timeStep);
+
+    // If the body state has changed, we have to update some informations in the rigid body
+    rigidBody->update();
+
 }
 
 // Update the physics simulation
 void DynamicEngine::update() {
-
     // Check if the physics simulation is running
     if (timer.getIsRunning()) {
         // While the time accumulator is not empty
@@ -79,7 +82,7 @@ void DynamicEngine::update() {
                 RigidBody* rigidBody = dynamic_cast<RigidBody*>(*it);
                 if (rigidBody && rigidBody->getIsMotionEnabled()) {
                     // Update the state of the rigid body
-                    updateBodyState(rigidBody);
+                    updateBodyState(rigidBody, timer.getTimeStep());
                 }
             }
 
diff --git a/sources/reactphysics3d/engine/DynamicEngine.h b/sources/reactphysics3d/engine/DynamicEngine.h
index 8744498c..92886e6e 100644
--- a/sources/reactphysics3d/engine/DynamicEngine.h
+++ b/sources/reactphysics3d/engine/DynamicEngine.h
@@ -43,14 +43,14 @@ class DynamicEngine : public PhysicsEngine {
     protected :
         IntegrationAlgorithm* integrationAlgorithm;        // Integration algorithm used to solve differential equations of movement
 
-        void updateBodyState(RigidBody* const rigidBody);                                                           // Update the state of a rigid body
+        void updateBodyState(RigidBody* const rigidBody, const Time& timeStep);                                                           // Update the state of a rigid body
 
     public :
         DynamicEngine(DynamicWorld* world, const Time& timeStep);       // Constructor
         DynamicEngine(const DynamicEngine& engine);                     // Copy-constructor
         virtual ~DynamicEngine();                                       // Destructor
 
-        void update();                                  // Update the physics simulation
+        virtual void update();                                          // Update the physics simulation
 };
 
 }
diff --git a/sources/reactphysics3d/engine/PhysicsEngine.h b/sources/reactphysics3d/engine/PhysicsEngine.h
index 9cdddf22..550b969f 100644
--- a/sources/reactphysics3d/engine/PhysicsEngine.h
+++ b/sources/reactphysics3d/engine/PhysicsEngine.h
@@ -58,7 +58,7 @@ inline void PhysicsEngine::start() {
 }
 
 inline void PhysicsEngine::stop() {
-    // TODO : Implement this method
+    timer.setIsRunning(false);
 }
 
 // Initialize the display time
diff --git a/sources/reactphysics3d/engine/Timer.h b/sources/reactphysics3d/engine/Timer.h
index 04f8221b..8c61fe36 100644
--- a/sources/reactphysics3d/engine/Timer.h
+++ b/sources/reactphysics3d/engine/Timer.h
@@ -112,11 +112,14 @@ inline void Timer::setCurrentDisplayTime(const Time& currentDisplayTime) {
 
 // Update the timer
 inline void Timer::update() {
-    // Update the current time of the physics engine
-    time.setValue(time.getValue() + timeStep.getValue());
+    // Check if the timer is running
+    if (isRunning) {
+        // Update the current time of the physics engine
+        time.setValue(time.getValue() + timeStep.getValue());
 
-    // Update the accumulator value
-    accumulator -= timeStep.getValue();
+        // Update the accumulator value
+        accumulator -= timeStep.getValue();
+    }
 }
 
 // Compute and return the interpolation factor between two body states