diff --git a/platformer.py b/platformer.py
index 054ae8b..cba2ba1 100644
--- a/platformer.py
+++ b/platformer.py
@@ -15,6 +15,8 @@ COIN_SCALING = 0.5
 
 # Movement speed of player, in pixels per frame
 PLAYER_MOVEMENT_SPEED = 5
+GRAVITY = 1
+PLAYER_JUMP_SPEED = 20
 
 
 class MyGame(arcade.Window):
@@ -76,7 +78,9 @@ class MyGame(arcade.Window):
             self.wall_list.append(wall)
 
         # Create the 'physics engine'
-        self.physics_engine = arcade.PhysicsEngineSimple(self.player_sprite, self.wall_list)
+        self.physics_engine = arcade.PhysicsEnginePlatformer(self.player_sprite,
+                                                             self.wall_list,
+                                                             GRAVITY)
 
     def on_draw(self):
         """ Render the screen. """
@@ -93,9 +97,8 @@ class MyGame(arcade.Window):
         """Called whenever a key is pressed. """
 
         if key == arcade.key.UP or key == arcade.key.W:
-            self.player_sprite.change_y = PLAYER_MOVEMENT_SPEED
-        elif key == arcade.key.DOWN or key == arcade.key.S:
-            self.player_sprite.change_y = -PLAYER_MOVEMENT_SPEED
+            if self.physics_engine.can_jump():
+                self.player_sprite.change_y = PLAYER_JUMP_SPEED
         elif key == arcade.key.LEFT or key == arcade.key.A:
             self.player_sprite.change_x = -PLAYER_MOVEMENT_SPEED
         elif key == arcade.key.RIGHT or key == arcade.key.D:
@@ -104,11 +107,7 @@ class MyGame(arcade.Window):
     def on_key_release(self, key, modifiers):
         """Called when the user releases a key. """
 
-        if key == arcade.key.UP or key == arcade.key.W:
-            self.player_sprite.change_y = 0
-        elif key == arcade.key.DOWN or key == arcade.key.S:
-            self.player_sprite.change_y = 0
-        elif key == arcade.key.LEFT or key == arcade.key.A:
+        if key == arcade.key.LEFT or key == arcade.key.A:
             self.player_sprite.change_x = 0
         elif key == arcade.key.RIGHT or key == arcade.key.D:
             self.player_sprite.change_x = 0