Today, we’re going to talk about time. Not time in the metaphysical sense, but the measurement of time. In most of the modern world, we use a number of common units of duration such as seconds, minutes, hours, days, months and years. Most of us have an intuitive feel for these units and are comfortable using them everyday to do things like setting alarm clocks, booking flights, paying for parking, remembering birth days etc. We even think of the system as a reasonably logical one – 60 seconds in a minute, 60 minutes in an hour, 24 hours in a days 365 days a year etc. Here, we shall take a look at how these intuitive models ignore some of the more bizarre aspects of time keeping. If not understood correctly, these mistakes creep into unexpected places, affecting everything from software systems, medical and aeronautical system to financial and legal frameworks.
I was flying last month to attend a graduation and it occurred to me that I was, in fact, flying in a large metal tub with metal flappy bits bolted on. How do airplanes fly? Well, they have wings. Duh! But why do wings fly? What makes a wing a wing? Can any flat sheet of metal be used? Why do planes only fly when moving? This is quite an interesting question indeed. The answer is quite subtle – subtler than you may think. It is in fact confusing enough that a lot of high school text books and a good chunk of introductory university physics textbooks explain it incorrectly. You may have been taught the answer in high school and you have just accepted it without thinking too hard about it. Read on if you wish to check if you were indeed taught correctly.
Last weekend, I put up a couple of ads on Craigslist for some of my old furniture and appliances – amongst them, a big rug. For those of you who have never heard of such a thing, Craigslist is an online, unsecured, unverified market place. You put up your ad for free and prospective buyers can contact you over email. You then haggle, arrange a rendezvous and exchange your wares. This is all well and good in theory, but in practice, things get a bit more…. interesting. Consider this reply that I received with respect to the rug that I put up for sale.
still available for sale? please let me know..
This is how most Craigslist conversations start. Very informal. Not much detail revealed besides an email address (and perhaps, a name).
It is for sale! You can reach me at XXX-XXX-XXXX. Let me know when you want to come pick it up.
So far so good.
Hi, Thanks for your response. I'm going on a vacation to London but I will instruct my assistant to prepare and mail your payment which I'm sure you will get in about 4 - 6 business days. I'll add $20 extra for the delay. I'll pay by M O or cashier check so send me your info (i.e full name, mailing address and your phone number) so payment can be mailed out immediately. I will also make arrangement for pick-up which will be after you must have received and cashed the payment.Awaiting your info.Thanks Frank
Now things are getting a little more interesting. How many of you think that this is reasonably innocent?
This is the last post in our series of posts on nuclear energy. Here, I shall describe the basic principles behind the design and continued operation of a nuclear reactor. In our last post, we looked at the techniques responsible for making fissile matter release energy as quickly as possible (in a nuclear explosion). Today, we will instead look at techniques to control nuclear fission reactions and usefully harness the resultant energy. Since there are a variety of various nuclear reactor designs and fuels, I shall stick to talking about a reasonably common (although a bit aged) design known as the pressurized-water reactor using U-235 fuel.
For those of you who are here from Skepchick (and the rest of you too), HI! Here is a little plug for other places you can follow Emma. Being a school teacher and applying to grad school, she has a number of compartmentalized blogging personas. This is where she explains interesting phenomena in science to lay non-scientists. She also rants about her life and her activism at http://sigstarskeptic.wordpress.com/ (which is quite new at the moment) and blogs about high-level chemistry (paper summaries for grad school and research) at http://blog.curiouschemist.net/. You can follow her at https://twitter.com/#!/sigmastarstate.
You’ve heard it all before, we need to find a new, sustainable, clean source of energy, and fast. People are looking to wind, solar, nuclear, and biofuels. But what do these things mean, really?
Today, I will discuss solar.
The sun is the main source of energy for this entire planet. We get much of our energy from coal and oil which is made of millions-of-years-old plant and animal matter. Animals get their energy from plants, which get their energy from the sun. The wind blowing your hair in your face and turning the wind turbines? That’s from the difference in temperature in different locations (due to the sun) and the rotation of the earth. Hydroelectric power like that made at the Hoover Dam? That’s from rainwater filling up a high altitude river source. What causes rain? The evaporation of water by heat from the sun, of course. As you can see, there are few sources of energy (nuclear and geothermal being the primary exceptions) which are not directly related to energy recently emitted from the sun. The problem with all of these forms of energy is that there is a “middle man” between the sun’s energy and usable electricity. Solar cells, which have been around since the mid-1950’s, attempt to dispose of the middle man allowing us to directly harness the power of the sun.