Here, you can find links to all sorts of online demos and animations!
How a Rotary Engine works
How Stuff Works: A site with explanations and examples of all types of inventions
Inner Learning Online - Human Body Demo
Kid's guide to Human Body Systems (contributed by Dakota Lowe)
A Nurse's Guide to the Human Body (contributed by Katie Gold)
Bacteria and Viruses: How Are They Different? (contributed by Eva Harris)