Posted: Jul 10, 2013 5:41 PM by Associated Press
Updated: Jul 10, 2013 9:12 PM
The plane that crashed at the San Francisco airport last Saturday was apparently going too slowly for a proper landing. It's airspeed was 103 knots but the minimum for a safe landing is 137 knots.
That brought up this question: How fast is a knot? Good Question.
Pilots and sailors use the term knot. It's a speed of 1 nautical mile per hour. That's equal to 1.15 standard miles an hour. So the plane was only going 118 land miles an hour but should have been at a minimum of 158 miles an hour.
The term "knot" dates from the 17th Century when sailors measured the speed of their ship using a line of rope with even-spaced knots tied in it. They lowered the rope off the back of the ship and let it pay out in the water while sailing onward.
After a specific time, the line was pulled up and the number of wet knots was counted to gauge speed.
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