diff --git a/Ball.cpp b/Ball.cpp
index f5b8933..1e24fdc 100644
--- a/Ball.cpp
+++ b/Ball.cpp
@@ -5,20 +5,20 @@
 Ball::Ball(Point& _center, double _min_height, double _v_x, double _p, double _q) :
     Center(_center),
     surface(_center, min_height, _p, _q),
-    init_h(_center.z),
+    init_h(_center.y),
     min_height(_min_height),
     bounce_number(0.0),
     crt_time(0),
-    A(_center.z),
+    A(_center.y),
     B(0),
-    U(sqrt(2 * G_CTE * _center.z)),
-    T(sqrt(2.0 * _center.z / G_CTE)),
+    U(sqrt(2 * G_CTE * _center.y)),
+    T(sqrt(2.0 * _center.y / G_CTE)),
     v_x(_v_x)
 {
 }
 
 void Ball::_compute_pos(double dt) {
-    Center.z = fmax(0.0, A + B * crt_time - (G_CTE / 2) * crt_time * crt_time + min_height);
+    Center.y = fmax(0.0, A + B * crt_time - (G_CTE / 2) * crt_time * crt_time + min_height);
     Center.x += dt * v_x;
     surface.update_center_pos(Center);
 }
@@ -66,7 +66,7 @@ std::ostream& operator<< (std::ostream &out, Ball const& data) {
     out << "t:" << data.access_crt_time() << ":";
     out << "T:" << data.accessT() << ":";
     out << center.x << ':';
-    out << center.y << ':';
     out << center.z << ':';
+    out << center.y << ':';
     return out;
 }
diff --git a/main_ball.cpp b/main_ball.cpp
index 00fb7c4..14e6f58 100644
--- a/main_ball.cpp
+++ b/main_ball.cpp
@@ -10,7 +10,7 @@ using namespace std;
 
 int main(int argc, char** argv) {
     int i;
-    Point center(0,0,10);
+    Point center(0,10,0);
     Ball ball(center, 0, 0.25, 1, 1);
     for(i=0; i< 10000; i++) {
         ball.update_pos(0.001);
diff --git a/spheroid.cpp b/spheroid.cpp
index 7fb8673..1e5be43 100644
--- a/spheroid.cpp
+++ b/spheroid.cpp
@@ -29,8 +29,8 @@ void Spheroid::update_center_pos(Point& _center) {
 }
 
 void Spheroid::check_horizontal_plan_collision(double& height) {
-    if ((center.z - p) <= height) {
-        p = fmin(init_p, center.z-height);
+    if ((center.y - p) <= height) {
+        p = fmin(init_p, center.y-height);
         update_radius();
     }
 }