The importance of wheels
http://www.mocomi.com presents: Why is the wheel so important to us? REQUIREMENTS A Book Straws A Table WHAT TO DO Push the book on the table with your hands. Bring the book back to position and place a few straws in it way and then push the book over it. WHAT HAPPENS When you push the books with your hands, you find that some amount of force needs to be exerted in order for the books to move. This is not the case when the books move over the straws and the effort required is a lot lesser. WHY THIS HAPPENS Since the surface of the table is not smooth enough, it causes friction, and therefore the force needed to move the book is alot more. When the book moves over the wheels, the surface is smoothened, and the friction is alot lesser. This is why the book moves better on wheels made of straw!