diff --git a/doc/index.html b/doc/index.html
index 9e73382..d5e32ff 100644
--- a/doc/index.html
+++ b/doc/index.html
@@ -398,6 +398,7 @@ The default up vector is (0, 0, 1).
 <p><tt>ag.setGravity(gx, gy, gz)</tt></p>
 <p>
 This function sets the gravity vector to (gx, gy, gz).
+The default gravity vector is (0, 0, -9.81).
 </p>
 
 <a name="ag_startFrame" />
diff --git a/tests/bowling.lua b/tests/bowling.lua
index 246ab77..7cd2726 100644
--- a/tests/bowling.lua
+++ b/tests/bowling.lua
@@ -53,6 +53,10 @@ function key_down_event(key)
     elseif (key == "c") then
         local c = ag.loadModel("crate")
         c:setPosition(-3, -3, 5)
+    elseif (key == "g") then
+        ag.setGravity(0, 0, 2)
+    elseif (key == "r") then
+        ag.setGravity(0, 0, -9.81)
     end
 end