diff --git a/Day01-15/10.图形用户界面和游戏开发.md b/Day01-15/10.图形用户界面和游戏开发.md
index ae65624..05d4bc6 100644
--- a/Day01-15/10.图形用户界面和游戏开发.md
+++ b/Day01-15/10.图形用户界面和游戏开发.md
@@ -249,12 +249,14 @@ class Ball(object):
         """移动"""
         self.x += self.sx
         self.y += self.sy
-        if self.x - self.radius <= 0 or \
-                self.x + self.radius >= screen.get_width():
-            self.sx = -self.sx
-        if self.y - self.radius <= 0 or \
-                self.y + self.radius >= screen.get_height():
-            self.sy = -self.sy
+        if self.x - self.radius <= 0:
+            self.sx = abs(self.sx)
+        if self.x + self.radius >= screen.get_width():
+            self.sx = -abs(self.sx)
+        if self.y - self.radius <= 0:
+            self.sy = abs(self.sy)
+        if self.y + self.radius >= screen.get_height():
+            self.sy = -abs(self.sy)
 
     def eat(self, other):
         """吃其他球"""