diff --git a/Ball.hpp b/Ball.hpp
index 4ddad91..a9ed49f 100644
--- a/Ball.hpp
+++ b/Ball.hpp
@@ -27,6 +27,7 @@ class Ball {
         double v_x, v_y;
         void _compute_pos(double dt);
         void _compute_v_x();
+        void _compute_v_y();
         void _compute_A_n();
         void _compute_B_n();
         void _compute_U_n();