Every equation tells the story of an experiment, but even the most enthused chemist would admit it’s no great yarn. Translate it into a computer simulation, however, and that dry string of characters becomes Dickens and Da Vinci rolled into one.

And it is not just equations that benefit from virtual experiments - any phenomenon that does not lend itself to a real-world investigation can be demonstrated by computer or manipulated to vary conditions or physical constants.

Schools with a Java-enabled browser, such as Explorer 4 and Navigator 4.2, will find a wealth of simulations on the World Wide Web. Java is the preferred programming language for these highly-interactive resources but it has its problems. Vernon Levy, head of science at Buttershaw Upper School, jokes that “you have to be a propeller head to understand it” and all simulations must be played online. In addition, the lack of a simple copy facility means you can’t save work and results must be noted manually. On the bright side, this simply means you take part in the simulation and for students that is a lot of fun.

Quality can be a problem and much of what is available on the Internet is US-orientated since teachers in the UK have authored little material. Numeracy-based subjects, where the answers are absolute, tend to make the most useful simulations.

One of the best collections is at the Virtual Laboratory of the University of Oregon. Simulations include that of a cannon, which lets you vary shooting angle, speed, wind and gravity pull to see how they affect a cannonball’s flight. The site also tackles thermodynamics and astrophysics. “Computer-based simulations can be useful for a trial run before students do the real thing,” says Levy.

The Virtual Laboratory also lets students collect data on variables and conditions they could never test - a simulation of gravity, for example, can be carried out on Earth, Mars or the Moon.

Students enjoy these pain-free practicals. “I wish I had known about this website before,” says 15-year-old Henry Procter, despairing of a potential energy experiment with a partner.

Another collection of simulations is the AnnenbergCPB Projects Exhibits website. Educators worked alongside a team of Web content experts, technical applications specialists and designers to provide an interactive, educational experience. Exhibits cover science, art, writing, literature, psychology and geology with a new exhibit added monthly.

The arrival of the Star Wars prequel makes topical the site’s “Lights Camera Action” exhibit, which asks: “What goes into the making of your favourite movies?” As well as writing dialogue for screen, the site lets you try your hand at being a producer. The challenge is to make a film about World War II. You have a set budget and must decide who is to direct the film, who will star in it, where the epic will be shot and how much will you spend on special effects. The simulation delivers its verdict on whether your movie was a financial and critical success or a flop. The activity works well with teams of three or four students, with the class later discussing the realities of the film industry; were the assumptions in the simulation valid; was it justified in rewarding you for selecting a big budget for special effects?

But not all subjects transfer well to simulation. Those involving human behaviour or interaction are generally less useful. For this reason history does not fare too well. Dave Martin, a history teacher who evaluates history links on the National Grid for Learning, sees a risk in simulations that allow you to change the course of history, for instance by boosting Harold’s arrow power so he wins the Battle of Hastings. “Students need to know the facts,” Martin says.

Simulations that represent three-dimensional worlds have their limitations, too - ecosystems, for example, can only be explored so far on a two-dimensional computer screen. The more successful sites overcome this problem by presenting visitors with a problem to solve. The Water Management Game, for example, empowers you as a lake manager to restore the quality of a lake and diversify its fauna and vegetation. Another site with an environmental theme is Recycle City; as town manager you must make the decisions that will clear the streets and parks of rubbish.

I found all the simulations mentioned by entering “java simulation” into metasearch engines at www.savvy.com and www.google.com. We also used Yahoo’s UK directory www.yahoo.co.uk. Java’s Developer site at www.developer.com is also worth checking; it has an education category that lists sites by subject and includes 60 links for primary schools.

But simulation is not restricted to the Internet. A host of CD-Roms use it and these may prove a more accessible source of simulations resources for primary schools. For example, Granada Learning’s Science Explorer I and Science Explorer II, for key stage 2, are collections of simulations. A host of simulation games are also available on CD-Rom. They tend to be more complicated than their website equivalents since they allow games to be saved and developed over time. The acclaimed Sim series by Eidos Interactive covers town management in Sim City and developing and managing tourist resources in Sim Safari.

No round-up would be complete without a nod to NASA. From the wealth of resources on its website, the Mars Lander game is a favourite. Or if that leaves you cold, visit its Wind Chill experiment, so you’ll know why you’re chilly on the beach this summer even though the sun is out. And while you’re in holiday mood, skip to one more site - a Java-simulated kite to fly.

* Websites

Virtual Laboratory jerser.uoregon.eduvlab

AnnenbergCPB Projects www.learner.orgexhibits

Water Management Game www.waterland.netrizawatmanframeindex.html

Dumptown www.epa.govrecyclecitymainmap.htm

NASA http:observe.ivv.nasa.govnasafunmarsmars.html

Stunt kite

www.best.combsteelejavakite.html

* CD-Roms

Science Explorer I and II from Granada Learning, pound;59 each for a five-user licence. Schools buying direct from www.granada-learning.com get a 15 per cent discount

Sim City 3000, pound;39.99, and Sim Safari, pound;14.99 (PC only), from Eidos Interactive, 01753 549 442. www.eidosinteractive.com