Archive for the ‘Wind velocity relative to force’ Tag

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! Continue reading

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