All the Answers
English language
In a schoolbag heavily ballasted. by textbooks and exercise books, there's never room for a dictionary, which is why the first bookmark you should add to your online reference library is Chambers. It offers the power of its 21st Century Dictionary (considered by many crossword-solvers and Scrabble-players to be the best in the business), plus its Thesaurus and Biographical Dictionary.
Maths
If you can't quite remember how to calculate the area of a circle, or you're not sure what is the definition of a cosine, find out here. This excellent maths reference site from the Faculty of Education at the University of Cambridge even lists the various processes of logic, so if you're not sure what an a priori argument is, then take a look.
Physics
How many metres in 100ft? How many acres in a hectare? How many grams (or ounces) in a heaped tablespoon of flour7 How does an oven temperature of gas mark 5 translate into degrees centigrade? Can you get your size 8 feet into European size 40 shoes? If it has to do with measurements, the answer is here; and the site can also advise you on a few formulae, such as calculating the right amperage of fuse to put in the plug of a 40-watt electric light.
Chemistry
Emerald, it
appears, is a form of a mineral called beryl, which is a compound of the metal
beryllium with aluminium, silicon and oxygen. That's the sort of thing you learn
from this point-and-click periodic table created by Mark Winter of the
University of
Sheffield, However, if you would prefer to know what an element looks like and
what happens when you allow it to get involved in a violent reaction, see
periodictable.com, the website of science writer Theodore Gray, the sort of chap
who accidentally drops sodium, which burns explosively on contact with water,
into his kitchen sink.
Science projects
It's always good to get a concise, simple definition of something. For instance, to read that a yurt is "a circular lattice-walled tent" adds to your knowledge, before you discover why that lattice helps make yurts sturdy and warm. Such concision is typical of the award-winning writers at How Stuff Works, which explains complex things comprehensibly and is also adept at exploring the science behind the news. Equally worth keeping an eye on is the "Science/Nature" section of news.bbc.co.uk, which last week was reporting that cows prefer to stand in a north-south alignment.
Geography
It has
recently been discovered that many mammals, including humans, have the ability
to smell danger - or, to put it another way, fear. Also that kangaroos have a
digestive system that produces much less methane gas than those of sheep or
cows, which could make them the ideal way to farm meat without adding to global
warming.
These stories give a taste of the news section of National Geographic, but the
best thing about this website is that it explores the landscapes and cultures of
the world in a way that makes you want to explore them, too.