diff --git a/Ball.cpp b/Ball.cpp
index 93bb674..b85d6fb 100644
--- a/Ball.cpp
+++ b/Ball.cpp
@@ -25,20 +25,22 @@ Ball::Ball(const Point& _center, const Ground* _ground, double _min_height,
 }
 
 void Ball::_compute_pos(double dt) {
+    double height = (*ground)(Center.x, Center.z);
     if (bouncing) {
         Center.y = fmax(
-            min_height,
-            A + B * crt_time - (G_CTE / 2) * crt_time * crt_time + min_height
+            min_height + height,
+            A + B * crt_time - (G_CTE / 2) * crt_time * crt_time + min_height + height
         );
     } else {
         double n_time = crt_time - stop_bouncing;
         double min_rad = radius - min_height;
-        Center.y = min_height + ((min_rad * (1.0 - exp(-n_time)) + min_rad )/2.) +
-            (min_rad - ((min_rad* (1- exp(-n_time)) + min_rad)/2.)) * sin(5. *
-                    n_time);
         v_x *= 0.8;
         v_z *= 0.8;
+        Center.y = height + min_height + ((min_rad * (1.0 - exp(-n_time)) + min_rad )/2.) +
+            (min_rad - ((min_rad* (1- exp(-n_time)) + min_rad)/2.)) * sin(5. *
+                    n_time);
     }
+    std::cout << (*this) << "\n";
     Center.x += dt * v_x;
     Center.z += dt * v_z;
     surface.update_center_pos(Center);
@@ -72,11 +74,12 @@ void Ball::_compute_v_z(Point normal) {
 }
 
 void Ball::update_pos(double dt) {
+    //double height = (*ground)(Center.x, Center.z);
     crt_time += dt;
     if ((bouncing) && (crt_time >= T)) {
         double old_t = T;
         double max_t;
-        Point normal = surface.getNormalVector();
+        Point normal = (*ground).get_normal(Center.x, Center.z);
         bounce_number += 1;
         _compute_U_n();
         _compute_A_n();
diff --git a/FlatGround.cpp b/FlatGround.cpp
index b3bf243..782f232 100644
--- a/FlatGround.cpp
+++ b/FlatGround.cpp
@@ -4,3 +4,7 @@
 double FlatGround::operator() (double, double) const {
     return 0. ;
 }
+
+Point FlatGround::get_normal(double, double) const {
+    return Point(0, 1, 0);
+}
diff --git a/FlatGround.hpp b/FlatGround.hpp
index e2ee420..74cd6e2 100644
--- a/FlatGround.hpp
+++ b/FlatGround.hpp
@@ -2,5 +2,7 @@
 #include "Ground.hpp"
 
 class FlatGround : public Ground {
-    double operator() (double, double) const;
+    public:
+        double operator() (double, double) const;
+        Point get_normal(double x, double y) const;
 };
diff --git a/Ground.hpp b/Ground.hpp
index c03f06a..66d8c98 100644
--- a/Ground.hpp
+++ b/Ground.hpp
@@ -5,4 +5,5 @@
 class Ground {
     public:
         virtual double operator() (double, double) const = 0;
+        virtual Point get_normal(double x, double y) const = 0;
 };
diff --git a/MarchingCubes.cpp b/MarchingCubes.cpp
index 48c4774..90d93a0 100644
--- a/MarchingCubes.cpp
+++ b/MarchingCubes.cpp
@@ -5,6 +5,8 @@
 
 #include "GL/gl.h"
 
+#include "GL/gl.h"
+
 MarchingCubes::MarchingCubes(
         const ImplicitSurface& surface,
         const Cuboid& box,
diff --git a/PerlinGround.cpp b/PerlinGround.cpp
index 081a46b..338bdc1 100644
--- a/PerlinGround.cpp
+++ b/PerlinGround.cpp
@@ -7,3 +7,8 @@ double PerlinGround::operator() (double x, double z) const {
     return surface.noise(x, z);
 }
 
+
+Point PerlinGround::get_normal(double x, double z) const {
+    const Point pt(x, surface.noise(x, z), z);
+    return surface.normal_at(pt);
+}
diff --git a/PerlinGround.hpp b/PerlinGround.hpp
index df2add7..597624c 100644
--- a/PerlinGround.hpp
+++ b/PerlinGround.hpp
@@ -7,6 +7,7 @@ class PerlinGround : public Ground {
         PerlinGround();
         PerlinGround(unsigned int seed);
         double operator() (double, double) const;
+        Point get_normal(double x, double y) const;
     private:
         PerlinNoise surface;
 };
diff --git a/main_bounce.cpp b/main_bounce.cpp
index 9f0aa65..b1849e8 100644
--- a/main_bounce.cpp
+++ b/main_bounce.cpp
@@ -11,7 +11,7 @@
 
 int main(int argc, char** argv) {
 
-    FlatGround* flat = new FlatGround();
+    PerlinGround* flat = new PerlinGround();
     GlutRender& render = GlutRender::get_instance();
     render.init(&argc, argv, 640, 480, "Bouncing stuff");
 
diff --git a/spheroid.cpp b/spheroid.cpp
index 4fc09b4..03cab7c 100644
--- a/spheroid.cpp
+++ b/spheroid.cpp
@@ -6,7 +6,7 @@
 #include <iostream>
 
 Spheroid::Spheroid(const Point& _center, double _min_p, double _p, double _q) :
-    ImplicitSurface(_center), normal_vector(Point(0,0,1)), min_p(_min_p),
+    ImplicitSurface(_center), min_p(_min_p),
     init_p(_p), p(_p), q(_q), stiffness(0)
 {
     _compute_volume();
@@ -44,15 +44,6 @@ Cuboid Spheroid::max_bounding_box() const {
     return Cuboid(_bd1, _bd2);
 }
 
-void Spheroid::check_perlin_collision(PerlinNoise perlin) {
-    double height = perlin.noise(center.x, center.z);
-    if ((center.y - p) <= height) {
-        p = fmin(init_p, center.z- height );
-        normal_vector = perlin.normal_vector(center.x, center.z);
-        update_radius();
-    }
-}
-
 
 double Spheroid::operator() (double _x, double _y, double _z) const {
             return (pow(_x, 2) / pow(q, 2)
diff --git a/spheroid.hpp b/spheroid.hpp
index b9549fe..5ca21e0 100644
--- a/spheroid.hpp
+++ b/spheroid.hpp
@@ -21,7 +21,6 @@ class Spheroid : public ImplicitSurface {
         void check_ground_collision(const Ground* ground);
         Cuboid max_bounding_box() const;
         void check_perlin_collision(PerlinNoise perlin);
-        Point getNormalVector() const { return normal_vector;}
         double operator() (double _x, double _y, double _z) const;
 
         virtual Point location_hint() const;
@@ -32,7 +31,6 @@ class Spheroid : public ImplicitSurface {
          * V is the volume. Extremely useful to have a constant volume in the
          * ball
         **/
-        Point normal_vector;
         double min_p, init_p, p, q;
         size_t stiffness;
         double V;