Demonstration of Centripetal Force

Because i often go to the internet for cool things to show my students, i thought i would go ahead and add this one that i discovered on my own to the information jungle... (I will try to come back and post pictures once I can again.) Non-science teachers will get a real kick out of this too, if you have access to the materials necessary.

Get a bag of marbles and a 500 mL Erlenmeyer flask.
First put just one marble in the flask, and grip the neck with your hand upturned (thumb down).
Get the marble going around the base of the flask, then turn it over.
Discuss as you twirl the flask why the marble is not escaping due to gravity.
Then bring your other hand to the mouth of the flask and press it against your palm.
Allow the marble to slowly drain from the flask.
Now add another two or three marbles, and try the trick again.
I think even you will be shocked at the motion of the marbles, and your students will be delighted!