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Interesting web sites

International System of Units (SI)
The US Metric Association’s website has a thorough section of the International System of Units Metric in minutes: the comprehensive resource for learning the metric system (SI) by Dennis Brownridge. It covers base units, prefixes and has a handy section on correct and incorrect usage.

Basic maths

MCA online (Learning units)
Maths Connexions for Adults is a website for TAFE students seeking help in maths. It is hosted by Victoria University (TAFE Division)

AAA Math
This American site is for elementary school students and teachers but is a good refresher for those who aren’t confident of their skills. It provides interactive math exercises. Not all the exercises from the associated CD are available online but quite a number are accessible.


Ask Dr Math
The Math Forum at Drexel University in Philadelphia is useful for students from primary to university level. The site is easy to search and also has a frequently asked questions section.

Numbers from the very large to the very small
Using the ‘powers of 10’ is an easy way to express both very large and very small numbers. For example, the Milky Way is about 1 000000000000000000 kilometres across. Instead of using 18 zeros to express this distance, we can use 10 18 (10 to the power of 18; may also be written as 10 ^18) —each zero represents one power of 10 (or one order of magnitude).

To represent very small numbers, a minus sign is added before the number in the superset. For example, a human cell is 0.00000001 of a kilometre, or 10 -8, in diameter.

(Bagenal, Fran, ‘Power of 10: measurements and scales’, University of Colorado, viewed 26 October 2005, <>)


Secret worlds: the universe within
To see of the powers of 10 in action, take a look at Secret worlds: the universe within. The Java interactive tutorial begins in the Milky Way, 10 million light years from Earth. It then ‘travels’ towards Earth, reducing its perspective by powers of ten as it finally moves into the subatomic world of electrons and protons on Earth. It’s quite a trip!

The site is produced by Molecular Expressions of the National High Magnetic Field Laboratory and the Florida State University Research Foundation in the United States.


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