Musings about science, technology, philosophy, religion, education.
Friday, November 12, 2010
Faster Than The Wind
I was wrong. A year ago, my future son-in-law asked me if a sailboat could travel faster than the wind. I said no. If the sailboat were travelling faster than the wind, then, to a person on the boat, the wind would seem to be coming from the opposite direction. This applies to downwind sailing, not to tacking against the wind. My mistake was going with my intuition, not my analysis.
I have studied many websites explaining how a sailboat can go (at an upwind angle) faster than the wind. Most explanations are flawed. Many quote Bernoulli’s principle, which isn’t an explanation. In the same way, physicists have stopped using Bernoulli’s principle to explain why planes can fly. (Otherwise, how could they fly upside down?)
Some websites contain text or comments from readers linking the claim that a wind-propelled craft, on land or water, can travel faster than the wind to a claim of perpetual motion. This, of course, is faulty thinking. Such a vehicle is getting its energy from the wind, and the wind is losing energy to the craft. No wind, no motion. Nothing magic about that.
But, for those still worried about what pushes a boat faster than the wind, here’s a simple explanation. First, what pushes a tacking sailboat forward against the wind? The answer is, the water. The wind pushes the sail, which is attached to the boat. The sail pushes the boat, which includes the keel. The keel pushes the water back (at a slight angle) and the water pushes the boat forward [Newton's 3rd, action and reaction.] Remove the keel (e.g.. raise the centerboard on a tiny sailboat) and the wind shoves the boat back, no matter which direction the boat is facing.
The faster a tacking sailboat travels, the greater the force of the wind on the sail, the greater the force of the keel on the water, the greater the forward force of the water on the boat. The limiting factor is not the speed of the wind but the friction of the water on the hull.
Going downwind faster than the wind (DWFTTW) is a little more anti-intuitive. A great blog entry with videos that demonstrates that an object can move faster than the object (and wind is millions of “objects”, air molecules) that propels it is http://dwfttw.blogspot.com/.
On Remembrance Day yesterday, someone I love and trust sent me a wonderful email about the origin of the bugle call Taps. It was beautiful, and inspiring, but fiction portrayed as fact. The PowerPoint presentation provided an alternate description of the composition of Taps and the tradition of playing it at military funerals and remembrance ceremonies.
The trouble is that the facts, and the real composer, got lost in the shuffle.
I find the prevalence of phony facts a big issue. Today, what is taken as fact is what one receives in one’s email. How long will it be before the real composer of Taps gets replaced in the history books?
One of my relatives forwards inspirational stuff to me regularly. It’s filled with ridiculous accounts of miracles, reports of events that never happened, stuff that can be easily verified as phony (like a reference to a non-existent doctor in a non-existent hospital in Boston.)
But if I point that out I am a party-pooper, I am negative, I am destroying her honest attempts to make other people’s lives better. (Other people = the hundred on her forward list.)
I suppose this isn’t different from 50 years ago when people would say, “I heard at the water cooler today that….” and pass on phony gossip. Yet, somehow, it is different. The water cooler is now as wide as the entire Earth. And we get the “news” from people we love and trust.
As an educator, and as a parent, I think it’s important that we instil in our students/children a healthy skepticism for what they read, even for what they see on the news. (For example, on 9-12, US radio stations carried the phony report that 9-11 attackers crossed into the US from Canada. The 9-11 Commission found that none did. Yet Homeland Security Secretary Janet Napolitano repeated it the claim in 2009, then corrected herself. And Sharron Angle, a Tea Party-backed candidate in Nevada, made that claim anew.) The trouble is, receiving the stuff in email from a person you trust is different from seeing it on the front page of the National Inquirer at the supermarket checkout.
I try to keep passing on the other-side-of-the-issue to people who send me preposterous reports. But should I use Reply or Reply All?. I sent a counterargument to a report of a miraculous treatment for some serious ailment that a sister-in-law sent to fifty people. I got roasted for the action by a person on the list worried that I had embarrassed her. After all, she was only trying to be helpful. Same thing when I sent a “don’t worry — it’s a hoax” about a phony virus notification forwarded by a relative to the dozen people on his list. Apparently, it’s better to let everyone worry about something untrue than correct the fact.
So, should I reply to the sender of the Taps email? If I did would I be “making a mountain out of a mole hill”, or “taking the joy out of a nice story?”
Well, I did send evidence of the more widely accepted credit for the origin of Taps to her alone and received an “I knew you would say that” rejoinder.