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Last updated: August 11, 2015

About this site

Who writes this stuff?

All the articles on Explain that Stuff are written by Chris Woodford, a British science writer with over 25 years of experience in explaining science and technology.

Is this site safe for children?

This is an educational website that I hope is safe and suitable for all family users, though it's mainly intended for ages 10+. We take our responsibility to young readers very seriously:

If you discover anything that you think may be inappropriate for young readers, please alert me straight away and I will try to put it right immediately.

External links

Please be aware that virtually all articles on this site contain links to carefully researched external sites for further reading (and they usually open in a new window so you can tell you're leaving this site). When I say "carefully researched external sites," I mean ones I have spent a lot of time looking for, which I hope will build on the information I've provided in my articles—books you might find useful, topical news articles, carefully vetted YouTube videos that demonstrate things right before your eyes, or whatever. I do not mean sneaky attempts to sell you garbage you don't want. There are absolutely no clandestine links of this kind, product placements, or paid links provided by manufacturers anywhere on this site. There are a few places where I link to manufacturers' websites for information about products because I've judged those to be the best sources of information; for balance, I try to include a number of different manufacturers wherever possible. The recommended book links generally take you to Google Books, not Amazon, because in my opinion that site provides the best catalog of the world's books currently available. These book links earn me no money; they're there because they're helpful, not because I am trying to sell you stuff. I go to great lengths only to include links to useful and reputable sites, and I do recheck links periodically, but—by the very nature of the Web—I have no control over, or responsibility for the content of, external sites. Again, if you find anything problematic, please do let me know.

Why explain stuff that way?

Here's a word or two about my pedagogical approach, for parents, home-schoolers, teachers and anyone else who's interested.

Our survey says...

Most people think science and technology is fascinating, fun, and incredibly important, yet they don't really understand it, even when they've studied it for years in school. How do I know this? Well... consider the findings of two recent surveys:

So people actually do like science and they do find it interesting, but they don't really understand it and they don't feel properly informed about it: somehow it just flies straight over their heads. That may be why so many children convince themselves science is hateful or boring in school... only to discover years later, as adults, that they actually quite like it! Whose fault is all this? I'm not sure—but my mission is to help put things right.

What I try to do is present often quite complex stuff in a way ordinary people can get a handle on. You'll find my articles are a bit different from the ones you get on other websites or in science books: I try to give you a good, clear, simple understanding of a subject rather than drown you in facts, details, and nit-picky trivia. Generally, my approach is to talk you gently around a subject, building on familiar stuff you're likely to understand already, a bit like a decent teacher would do.

Why simplest is best

After studying science for about 35 years, and writing about it for over 25, I firmly believe that it's better to completely understand a small amount about something—the essence of how something works or the science behind it—than to know vast amounts of non-essential details that don't fit together in your mind and don't make sense. In my book (and some people will strongly disagree with this), it's even okay to have a slightly wrong or oversimplified understanding of something than a totally correct misunderstanding. So, for example, I think it's much better if children have a firm, oversimplified understanding that electrons "whiz around" atoms that they can explain to a friend than some sort of fuzzy, confused (but scientifically more accurate) idea about orbitals and probability that they barely understand and could never explain to anyone else. This is not an excuse for dumbing down: it's an argument for teaching with sensitivity—understanding your audience and what they need to know. You can always build on a firm, simplified understanding (or correct, tweak, or qualify it) later on; you can never build on confusion. And if you turn people off too soon, you may well lose them forever. What good is that?

Learning lessons from other websites

This website is not supposed to be anything remotely like Wikipedia—and for a good reason. I value Wikipedia very highly and I think it's an absolutely superb contribution to collective knowledge. But it has serious shortcomings as an educational tool because it fails to take account of a simple fact that is blindingly obvious to any teacher: readers of different ages and abilities have very different levels of understanding and need very different kinds of information. Many Wikipedia articles (especially the scientific and technical ones) are now written by self-professed "experts," for themselves and their friends—people who take too little time to consider how to explain things clearly to general readers (or young students). As time rolls on, simple outline articles ("stubs") become longer and more complete, but they often become more complex and convoluted and harder to understand at the same time. (One of my favorite examples is Wikipedia: Entropy, an article so impenetrable to general readers that it has now spawned an offspring called Wikipedia: Introduction to Entropy, which, in my opinion, now merits its own "Wikipedia: Introduction to Introduction to Entropy" that ordinary people (and students under the age of 18) might just have a hope of understanding. I say this as someone who studied thermodynamics to degree level. That's just one random example. Take a look at Wikipedia: Refractive Index for another example. Lots of great information, if you happen to have a degree in physics, but most of it entirely unsuitable for most of the readers who will look at it—typically, I would guess, younger teenagers seeking homework help.) In short, Wikipedia's problem is that its writers start off from what they're burning to say rather than from what people want and need to know; a good teacher or educator will always start from the audience.

Of course there are plenty of websites besides Wikipedia, but quite a lot of them merely describe gadgets and technologies without explaining them or putting them into a broader context. That's sometimes because the people who write them don't have a rich enough scientific understanding. But it's also because many websites contain vast numbers of bitty articles written by separate authors and, unlike in book publishing, there's no editor to give the whole thing an overall structure and ensure all the articles work together as a coherent whole. My approach is much more book-like. The emphasis here is on gently building knowledge and understanding, not filling people's heads with undigested confusion. Apart from explaining how things work, I try to get across the fundamental scientific principles behind things so you can make the connections, see the patterns, and figure out how everything links together. So while I have (for example) articles about toasters, loudspeakers, and refrigerators, they're also quietly teaching you the science of heat, electromagnetism, and thermodynamics. Learn the basic science behind a few things and you can figure out the technology of quite a lot of other things. This website is book-like in another important way too: I write everything on the site, so I know exactly how all the articles work together. Over a number of years, I've figured out which articles I need to add to make a very comprehensive collection that works as a coherent whole, in much the same way as a printed book. In one important way, the website is very unlike a book: it's being continually revised and improved to take account of new information and feedback from readers. Every article clearly states at the start when it was last updated.

Learning from history

Tech websites have a very unfortunate obsession with newness and fads; Twitter (for all its good points) encourages a tendency to recycle ("share") items of current science news, often making matters worse. How many people who fell over themselves to "retweet" stories about neutrinos breaking the speed of light had the slightest idea why the probability of that scientific finding being correct was so incredibly slim? In sciences such as physics, chemistry, and biology, the core, bedrock stuff you need to learn is years, decades, or even hundreds of years old and much of it will never change. (That's a measure of how excellent the work done by people like Newton, Maxwell, and Einstein really was.) In a subject like physics, the stuff people learned in schools and colleges 50 years ago is still the essence of what children need to understand properly today before they surf the flotsam and jetsam of the new. That's why we can (and should) still read and admire lectures delivered in the 1960s by such great scientist-educators as Richard Feynman; they are just as relevant today. You can't properly grasp any invention, machine, or cutting-edge technology if you don't properly understand concepts like electricity, magnetism, heat, atomic structure, the laws of motion, the kinetic theory, the conservation of energy... and so on. Those are the sort of topics that I drum home on this website, carefully disguising them as articles about interesting everyday things!

Even for cutting-edge science and technology, historical background is really important. That's why there's a full timeline on this site, indexing most of the inventions and discoveries chronologically. Over the last couple of years, I've also come to the conclusion that inventions can be explained more richly by referring to original patent drawings, particularly if they're color-coded and annotated simply. If you want to understand an invention like the laser printer, you can do it by looking at the components inside and seeing how they form a logical sequence. But you can also do it by going back to Gary Starkweather's (the inventor's) original patent and noticing that he invented the laser printer by bolting a laser scanner on top of a conventional photocopier. That explains why laser printers and photocopiers have so much in common. A lot of my articles now contain details of patents to give readers a richer understanding of how things worked and why inventors solved problems a particular way.

Anyway, that's where I'm coming from—and it's quite enough pedagogy for now! In a nutshell: this site is dedicated to helping people learn useful things about everyday stuff in an interesting way. I've spent over six years (so far!) putting it together and I really do hope you enjoy it. If not, do please write and tell me. Good or bad, your feedback is always interesting to me and always welcome.

How does this website support curriculum learning and home-schooling?

You'll find detailed help in our teaching guide, which shows how our articles map to different parts of a typical science curriculum for students aged 10–18.

Why do you only write about science and technology?

I want the material on the website to be of a high standard, so I write about only the things I feel qualified or knowledgeable enough to write about: physical sciences, technology, engineering, environmental issues, and computing. To write a really good explanation, you have to understand something very well indeed; when people write about things they don't understand, it's very obvious—and it's not fair on readers. Unfortunately, I don't know enough about life sciences, economics, law, politics, and so on to write well about those other topics. Maybe at some time in the future I will come across someone who can do those things for me!

Why do you use metric units? Why do you spell SI units "meter" and "liter"?

This is a scientific website so we follow the convention of using metric and SI units (such as meters and kilograms), though we generally give Imperial conversions in brackets. Like many US science publications and textbooks, we have decided to follow the US National Institute of Standards and Technology convention, based on Webster's (US English), rather than the Oxford (UK English) convention:

"(i) The spelling of English words is in accordance with the United States Government Printing Office Style Manual, which follows Webster's Third New International Dictionary rather than the Oxford Dictionary. Thus the spellings "meter," "liter," and "deka" are used rather than "metre," "litre," and "deca" as in the original BIPM English text".

Using material from this website

Please note that different rights apply to the words and the pictures on this website. Briefly:

Here's a more detailed explanation if you need it...

Using our words

Can you copy and use articles from this website on your own website? We're very sorry, but we do not permit people to copy articles from onto other websites (including blogs, Facebook pages, and other personal sites) for any reason whatsoever.

Fair use ("fair dealing"), such as briefly quoting from our articles for purposes of commentary or discussion, is fine, providing you cite this website as the source of your quote. Fair use does not allow you to republish extensive or entire copies of our articles and use them as you wish on other websites, or elsewhere, even if you're doing so for noncommercial or educational purposes. Please note that we will generally regard copying anything more than about a couple of paragraphs and any unattributed quotation (passing our material off as your own) as copyright infringement. Please be aware that all the articles on this website are either registered at the US Copyright Office (or deposited there pending registration), which means deliberate copyright infringement can make you liable for severe financial and even criminal penalties. We routinely scan for unlawful copies of our articles and we take some kind of action in every case of copyright infringement we find. We take this matter extremely seriously and employ law firms in Europe and North America to help us deal with the problem.

The simplest way to avoid any kind of copyright problem or misunderstanding is to ask for permission. Please feel entirely free to contact us if you have any queries, you'd like to discuss reprinting or reusing our articles, or you'd like us to confirm whether some use you have in mind is "fair use" or otherwise okay. We are always happy to help—and generally we'll reply within a day or so.

Using our pictures

Can you copy and use our pictures? Broadly speaking, if you're not using them to make money, yes, with pleasure! But do read on.

The photos and artworks on this site fall into three different groups:

  1. Any images and photos used on this website are believed, in good faith, to be in the public domain if they are credited to US federal government agencies such as NASA, the US Department of Energy, or the US Military (US Army, US Air Force, US Navy, US Marines), or their employees. We have taken reasonable steps to check each image, but we cannot and do not guarantee its copyright status. If you want to reuse one of these photos, it's your responsibility to confirm the copyright status for yourself. In case you're wondering, we have sometimes "cropped," blurred, scrambled, or otherwise disguised people's faces in public domain photos to protect their right to privacy. It is our policy to give individual photographers full credit for their work whenever we possibly can and we would suggest you do the same.
  2. We also use a few photos from Flickr that are published under various Creative Commons licenses. Please note that these photos are still protected by copyright and their owners kindly grant us permission to use them, but only if we follow their conditions (the licence, in other words). If you wish to reuse these photos on your own website, please be sure to follow the licence exactly. Usually that means you have to credit the original photographer (which is only fair) and repeat the licence. If you're not sure, copy the exact words we've used to credit the photographer and the link to the Flickr and Creative Commons websites and you should be OK. (We return the favor to the Flickr community by offering our own photos for reuse on our Flickr page, all under a Creative Commons licence.)
  3. Creative Commons License Any other photos or artworks that are not attributed are ones we have created and you're welcome to use and reuse them for noncommercial purposes only under the terms of the Creative Commons NC-SA license. For the avoidance of doubt, please note that "noncommercial" means you may not charge a fee for the use of our work, use it in any for-profit publication (whether educational or not), use it to sell, endorse, or promote any product or service, or earn any money from it by advertising or any other means whatosever, irrespective of whether you make a profit. Hi-res versions of a few of our photos are available for commercial use, under license, on our Flickr page; other photos are available in high resolution on request. Please would you kindly attribute any images we've created by crediting and making a link to the page on our website where the original image appears. Some HTML along these lines would be just great, thanks:

    Image from <a href="">Explain that Stuff</A> published under a <a href="">Creative Commons License</a>.

Hotlinking to our pictures from your pages

Hotlink artwork

If you would like to use images from this site, you'll need to copy and upload them to your own server rather than linking directly to them ("hotlinking"). Please note that image hotlinks to are automatically blocked. If you link to our images directly from your own pages, you'll find a dummy placeholder image (right) appearing instead of the picture you actually want. Or you may find your images suddenly disappear without warning when we change the image addresses (as we do regularly). Worry not. To get the correct image, all you need to do is copy it to your own webspace: right click on the image you want, save it to your hard disk, and then upload it to your own web server as though it were a file you created yourself. If you have problems, send us an email and we'll try to help.

Would you like to license our photos or artworks for commercial use?

Privacy policy

You'll find the full privacy policy for this website on our privacy policy page.

Permission to reprint in books

Since this website is all about science education, we're happy to discuss requests for limited reuse of material from this website in educational books and other materials, but (as explained above) not on other websites or in any other material that appears online. Now all books are educational in some sense, but by "educational books" we mean very specifically textbooks, other books geared to school and college students, or those primarily produced by the author for educational reasons.

Please kindly send us details of your publication, intended audience, approximate print run, publisher, and anything else you think might be relevant, and specific details of the material you'd like to use, and we'll let you know what's possible (usually the same day). Please note that if your use is commercial (for profit), we will normally charge a licensing fee. If you're a nonprofit or charity educational publisher, we don't normally charge. Please see our licensing page for more details about licensing fees and commercial use.

How (and when) should I cite your articles?

When to cite

It's often a good idea to acknowledge the source of articles you use—and absolutely required by many schools, colleges, and other academic instutitions. If you're quoting verbatim from something, citing a source is the way to avoid problems of plagiarism; it's also generally a requirement if you're claiming "fair use" (fair dealing) of copyright material. The way to cite a web page varies according to the citation style you're using (if no-one has told you which style to use, it doesn't matter). Most of our articles have ready made cut-and-paste citations at the bottom of the page. A few articles may still be missing them. In that case, please use a citation like this in your bibliography, references, or footnotes:


For example:

When not to cite

Wikipedia users have become obsessed with finding sources and citations, which is generally a good thing—but only if you understand the difference between reliable and unreliable sources. I do not claim to be an expert on many things; I am an educator: my articles are general and educational and should not be cited as definitive sources of factual information (Beethoven's birthday, the population of Fiji, the melting point of iron).

I am a teacher. Can I print and use material from the site in class handouts?

If you are teacher or professional educator, you are most welcome to print and circulate up to 200 copies of any article as a handout (or other teaching material) for classes within your own school or college, providing you do so for free. You do not need to ask permission, but please kindly credit this website as your source. I consider this a perfectly fair use—and something I would warmly endorse and encourage. However, please kindly do not copy articles verbatim onto publicly accessible school or educational websites.

Copyright and legal information

You'll find this on our copyright and legal notice page.

Why is your website running intrusive advertisements that seize control of my computer?

As far as I know, it isn't! This website runs as little advertising as it possibly can (two relatively small ad squares) to help pay its costs. Occasionally, people contact us to say that they have seen very intrusive or distracting advertising while viewing one of our pages. We do not run intrusive advertising of this kind. We don't run any pop-up or pop-under ads, any ads that seize control of your browser, or any ads that redirect you to another site when you leave our pages. If you're seeing ads like this, it means your browser or computer has been hijacked by malware (malicious software). You need to run antivirus and anti-malware scanners immediately (such as Microsoft Security Essentials and the Windows Malicious Software Removal Tool). If you're running Windows, please check out Microsoft's guide to fixing a hijacked web browser.

Advertising on this website

Sorry, you cannot place direct advertisements on this website. We do not accept any direct advertising at the moment; all our advertising is coordinated through Google Adsense.

We do not sell links: you cannot pay to place text links anywhere on this site (even "nofollowed" ones). We do not, never have, and never will sell links and we will not reply to any emails we receive asking to buy links.

Would you like to switch your advertising to our network?

In a word, "no". Thank you for considering us, but we are very definitely not interested in using any other advertising providers at this time and we will not run trials of other ad networks. We're very sorry, but we will not reply to speculative emails from advertising providers.

Would Explain that Stuff like to join my affiliate scheme?

We're not interested in affiliate schemes, referrals, or any other similar programs; we've tried them, they don't work on this site, and we won't be trying any more of them. Thanks all the same.

Link policy

I'd like to buy this website/domain. Is it for sale?


Will you syndicate your articles to us to publish on our site?

We're very sorry, but we are not interested in syndicating articles to other websites. We do not allow our material to be copied or published by other websites for any reason and we will take action against unlawfully copied material whenever we find it.

Will you license your articles to us to use offline?

Please see our licensing page for more details.

How do I license a photo/artwork for commercial use?

Please see our licensing page for more details.

Do you accept articles or submissions written by other people?

Sorry, but we only publish our own material. There are absolutely no exceptions to this. Thanks for the thought, but we are not interested in publishing articles by anyone else, for any reason, even if they're supplied for "free."

Will you write something for me?

Please see my author page for more details.

Contacting us

We're very sorry, but we cannot provide extra information about any of the articles on this website or help students with projects, essays, or schoolwork. We're really sorry about that, but there just aren't enough hours in the day and school assignments are meant to test your abilities, not ours!

Found a mistake?

If you find any errors or inacccuracies in any of the articles, if something really confuses you and you think we should reword it, or if you'd like to suggest any other improvements, please do get in touch. We'd be very pleased and grateful to hear from you. We do our very best to fix mistakes immediately (usually the same day we hear about them).

You can send us a general email using the email form; to send feedback on an article, please use the feedback form.

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