diff --git a/Ball.cpp b/Ball.cpp
index 390fa56..0201912 100644
--- a/Ball.cpp
+++ b/Ball.cpp
@@ -41,24 +41,27 @@ void Ball::_compute_U_n() {
     U *= 0.5;
 }
 
-void Ball::_compute_v_x() {
-    v_x *= 0.5;
+void Ball::_compute_v_x(Point normal) {
+    double factor = normal.x / (4*(normal.x + normal.y));
+    v_x *= (0.5 + factor);
 }
 
-void Ball::_compute_v_y() {
-    v_y *= 0.5;
+void Ball::_compute_v_y(Point normal) {
+    double factor = normal.x / (4*(normal.x + normal.y));
+    v_y *= (0.5 + factor);
 }
 
 void Ball::update_pos(double dt) {
     crt_time += dt;
     if (crt_time >= T) {
+        Point normal = surface.getNormalVector();
         bounce_number += 1;
         _compute_U_n();
         _compute_A_n();
         _compute_B_n();
         _compute_T_n();
-        _compute_v_x();
-        _compute_v_y();
+        _compute_v_x(normal);
+        _compute_v_y(normal);
         std::cout << "New bounce :";
         std::cout << "U:" << U << ":";
         std::cout << "A:" << A << ":";
diff --git a/Ball.hpp b/Ball.hpp
index a9ed49f..9f2d90e 100644
--- a/Ball.hpp
+++ b/Ball.hpp
@@ -26,8 +26,8 @@ class Ball {
         double A, B, U, T; // Coefficients for the physical model.
         double v_x, v_y;
         void _compute_pos(double dt);
-        void _compute_v_x();
-        void _compute_v_y();
+        void _compute_v_x(Point normal);
+        void _compute_v_y(Point normal);
         void _compute_A_n();
         void _compute_B_n();
         void _compute_U_n();