Event.observe requires the Prototype JavaScript library loaded. If its not loaded and you try to use it you will get the error "Event is not an object"

You need to include that in your &lt;head&gt; as follows :

&lt;script src="/path/prototype.js" type="text/javascript"&gt;&lt;/script&gt;


How to access Event object inside javascript tag of Aspx page header content?
I've learned in that in this experiment:



...the skater will start rotating faster when she brings her arms in and there is no net torque acting on her. But what would happen to her angular momentum and rotation if she only brings one of her arms inwards with the other arm sticking outwards?

edit: will a net torque act on the body? What will this cause?
