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?