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The FREE online science and technology book

CCD chip from a webcam.

Breathless by Chris Woodford paperback book cover rendered as dummy book.

Want to know why giant ships can float, how your earbuds make music, what graphene is, or how windows can clean themselves? You've come to the right place! Here you'll find simple explanations you can really understand—hurrah!

Hard stuff... made simple!

Explain that Stuff is an online book written by science writer Chris Woodford (author of many popular science books for adults and children). It includes over 400 easy-to-understand articles, richly illustrated with clear artworks and animations, covering how things work, cutting-edge science, cool gadgets, and computers. We take the "pain" from explain and the "tough" out of stuff! There's more information on this website than in your average expensive science book, it's continually updated, and it's completely free to use! Explain that Stuff also helps to support curriculum learning (conventional STEM education and home-schooling).

How to use this site

There are five simple ways to find what you want:

Icon for browsing A-Z.  A-Z index: Browse articles by name, from accelerometers to zeolites... via induction motors, LCDs, and regenerative brakes.

Icon for browsing by date  Timeline: Find inventions by date, from the prehistoric birth of solar energy to the development of quantum computers.

Icon for random article  Random: Discover something new. Keep hitting "random" till you find something you like.

Icon for search engine  Search: Use our safe, Google-powered search engine.

Icon for loving STEM  Teaching guide: Browse a typical school curriculum to match articles from this site to topics you want to study or teach.

What's hot in January 2022?

In the news now...

Gold mirror segment from the NASA James Webb space telescope


NASA's James Webb Telescope has blasted into space carrying some of the most sophisticated mirrors ever developed. How do mirrors do their shiny stuff... and do they really flip things side to side as the science books tell us?

How a solar cell works.

Solar power

Can the Sun save us? According to the US Energy Information Administration, solar made just 3 percent of US electricity in 2020, but that figure will reach 20 percent by 2050. Just in time... or too little too late?

Conceptual artwork of quantum computing.

Climate change

Last year was the sixth hottest on record, tied with 2018, but the hottest ever for almost a quarter of the world's people. If you find the whole subject of "global warming" baffling, try our ever-popular, simple introduction—completely updated for 2021.

A NASA Ames scientist demonstrates virtual reality headset and data gloves

Virtual reality

Facebook's having another go at moving us into its virtual dream-world; it's latest effort is called the "metaverse." But what is virtual reality... and where did the idea come from?

What's new for '22?

We have a few brand new articles on the site... and more to come in the next few months:

A computer with a brain on its screen, illustrating the concept of AI

Artificial intelligence

Can we imagine a world where computers are smart enough not to need us?

How gravity is seen as space-time curvature in Einstein's general theory of relativity


It's taken over two millenia for people to understand how gravity holds the universe together. What do we know so far about this most mysterious of forces?

Solar-powered airplane by NASA.

History of flight

How did humans soar to the sky... and why did it take us so long?

Giant pulley wheels in a large crane


The science behind cranes is easy to understand, but why are there so many different types? How much can they lift... and what stops them toppling over?

James Clerk Maxwell

History of electricity

Why did it take so long for people to harness electricity? We explore the sparky story of electric power.

Black laptop computer loading software from an open red DVD


Computers are wonderful machines you can reprogram to do almost anything. How does "software" make that work?

Cartoon art of a rat undergoing intracranial self stimulation, ICSS, in the Olds and Milner experiment.

Great psychology experiments

People are never quite what we seem—as these 10 fascinating experiments from psychological science clearly demonstrate!

A NASA Ames scientist sets up an experiment using sand and green lasers.

What is science—and why does it matter?

Why is science still our best hope for making sense of the world?

Gray plastic Hitachi transistor radio

History of communication

How did we get from the alphabet to the Internet in about three to four thousand years?

Most popular

Model of a steam turbine at Think Tank science museum, Birmingham, England.

These are some more of our classic, ever-popular articles:

  1. Water pollution: Rivers and seas take a long time to recover from the effects of careless human treatment. What causes pollution and what can we do to stop it?
  2. Electricity: The most versatile and useful form of energy in our world, electricity is going to become a whole lot more important in future.
  3. Nanotechnology: Can we build a brave new world just by shuffling atoms and molecules under a microscope?
  4. Magnetism: One of the first bits of science people studied, magnetism is still just as relevant today in everything from electric cars to body scans at the hospital.
  5. Gears: Wheels with teeth carved around them can make you go faster or bump up your power—and here's how.
  6. Batteries: We all need electricity, wherever we happen to be, so thank goodness for batteries—miniature power plants you can carry in your pocket.
  7. Electric motors: These amazing machines turn electricity and magnetism into movement, powering everything from handheld toothbrushes to bikes, cars, and trains.
  8. Cloud computing: Why buy yourself an expensive computer or programs to go with it when you can get access to something just as good over the Internet?
  9. Global warming: Is the planet really heating up? What can we do about it?

What else is on our site?

Optical mouse circuit board with red LED light shining through light guide.

The articles on our site are divided up into broad topical areas, listed below. We've also given you a rough idea of the kind of questions you're going to find answers to in each section:

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Our website serves advertisements to pay its running costs. The advertisers we work with use a technical mechanism called cookies (small files stored on your computer) to help them serve relevant and useful advertisements that they think are likely to appeal to you, but you can opt in or out of these cookies at any time. The web domain does not collect, store, sell, or share any personal information and has no plans ever to do so in the future. However, in line with the California Consumer Privacy Act (CCPA), you may still send us a "Do Not Sell My Personal Information" request if you'd like to. For more details, please see our privacy policy.

Please do NOT copy our articles onto blogs and other websites

Articles from this website are registered at the US Copyright Office. Copying or otherwise using registered works without permission, removing this or other copyright notices, and/or infringing related rights could make you liable to severe civil or criminal penalties.

Text on this website is copyright © Chris Woodford 2000, 2022. All rights reserved. Full copyright notice and terms of use.

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