THE FORCE OF WIND – A GREAT SURPRISE FOR MOST PEOPLE

Moving along under a light breeze - working upwind with sails sheeted in close.

Please left-click this image for enlargement.

In order to changes gears for a moment, I’ve inserted a photo of a form of travel, recreation, and sport that utilizes the wind.  The image above is of my little sloop, Nature’s Way.  It was taken by my wife from a position onshore.  The craft has a fixed shoal draft keel that accounts for one-third of the weight (displacement) of the craft (1,100 pounds).  In spite of the keel, she is very easy to launch from the trailer and also easy to retrieve – pretty much a one-person job.  I wish for everyone that they could experience such peace as is provided by sailing in fair weather.  However, experienced sailors know that when the wind picks up, the force from it increases exponentially.  If they don’t know that fact and the wind velocity increases more quickly than they anticipate they are likely to some day find themselves in a position where they have waited too long to reduce the sail area.  Then they will have their hands full – especially if sailing solo.

This image shows the craft moving 45° “off the wind.”  In other words, under skillful hands the boat is being “pulled” as well as pushed by the wind in a general upwind direction.  Most sailboats with this type of rig can sail 45° off the wind but no closer than that.  However, by zig-zagging from one tack point to the other, the boat can reach an upwind objective.  It reminds me of working upslope on a mountain trail by taking a switchback route, rather than climbing directly upward.  SO, DON’T THINK THAT SAILBOATS ONLY SAIL IN THE GENERAL DIRECTION OF THE WIND – THEY CAN ALSO SAIL IN A GENERAL UPWIND DIRECTION AS IS BEING DONE IN THIS IMAGE (though there is about a 90° degree arc – 45° degrees on either side of the wind-line that they can’t sail effectively).  To be thorough I must add that some extremely well-designed boats with well-cut sails can get closer to the wind with a skillful skipper.

A sailboat can also sail nicely broadside to the wind.  That position is called a beam reach.  In time, for those of you who are interested, I will probably post a little tutorial on the points of sailing.  For now, I hope the image below with some elaborations will whet your appetite.  To reach it you must click the enticement to read on when you reach it at the end of the next paragraph.  Now – LET’S DISCUSS THE POWER OF A STORM’S WIND OR ANY OTHER WIND ACCORDING TO ITS VELOCITY:

There are some widespread misconceptions about the relationship between the wind’s velocity and the force it is able to exert.  Doubling the wind velocity quadruples the air’s potential force upon a surface that it strikes at right angles.  Early on in my teaching career it because quite apparent to me that most people assume that doubling the velocity simply doubles the force.  But that is far from true.  For example, a 110 mph wind has 4 times the potential force of a 55 mph wind!

Let’s compare 140 mph winds to 100 mph winds.  Those who have not learned the physics of the relationship between velocity and force generally deduce that an increase from 100 to 140 would be an increase of 40% not only in the wind velocity but also the potential force of the wind.  The former would be true but the latter is not true- not even close.  This is because the square of the velocity is proportional to the force (V2 = F).  A constant must be inserted into the equation in order to express an actual unit of force but that is not necessary in this discussion.  If you square 100 you will get 10,000.  If you square 140 you will get 19,600.  So the force upon a surface that the wind is striking at right angles will increase from 10,000 “units of force” to 19,600 “units of force.”  THAT IS A 96% INCREASE IN FORCE! (derived from 9,600 – the increase – divided by 10,000 the beginning force).  In other words, if a 100 mph wind increases by 40% its potential force almost DOUBLES!

Believe me, as one who experienced the aftermath of hurricane Andrew (our house in Homestead was a total loss) you do not want to be sharing space with a 140 mph hurricane.  It definitely won’t be a party!

Please, if you are located where Ike might visit – think in terms of protecting what you are able to protect in the short time remaining – then evacuation.

Please visit the rest of this web-log at https://cloudman23.wordpress.com/.  If you are interested in weather, there are some tutorials scattered about and more will be added in time.  At the end of this page there is a cue to click to the previous page or the next page.

3 comments so far

  1. Antoinette on

    That really does look a beautiful boat….does she have a name?

  2. Tonie on

    Yes Antoinette – thanks for asking. In 1981 my paternal grandmother died. When I was consoling my grandfather, a hard-working farmer, he responded, “Well, son, that’s just Nature’s Way.” 8 years later, when I purchased this boat, I gave it that name, “Nature’s Way.” My being in the geosciences gave the name even more appeal because, after all, I’ve spend a great deal of time studying Nature’s way. Also, I’m mindful, as I’m plying relatively quietly through the water, that I’m using the wind which Nature has provided. I rarely have to fire up that little outboard kicker so I get great mileage. LOL

    Incidentally, with the bowsprit the boat length is about 17′. It’s a shoal draft sloop with a ballasted keel – easy to launch and retrieve. It draws only 18 inches – hard to believe, I know. It helps me to hold on to that one remaining thread of sanity that remains – the loss of the rest attributed to so many years living in populous South Florida.


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