Throughout history, people have used many methods to clean their teeth. Some ancient people chewed on frayed twigs. Others rubbed their teeth with cloth or swabbed them in vinegar. The Egyptians may have been the first people to use toothpaste when they mixed powdered pumice (a porous rock formed in volcanic eruptions) with vinegar and applied it to their teeth in the 100's B.C. Some toothpastes still contain pumice, but science has since supplied other toothpaste ingredients that the ancient Egyptians never dreamed existed.
Pi is an extremely interesting number that is important to all sorts of mathematical calculations. Did you know it can be calculated without the use of circles? Find out how you can calculate it yourself.
Iran has announced its activation of a second set of uranium centrifuges. These machines are at the core of the uranium-enrichment process. Find out where the centrifuge fits into the equation.