Results 1 to 4 of 4
Thread: Joint Variation

20131002, 12:25 #1
 Join Date
 Jan 2001
 Location
 La Jolla, CA
 Posts
 1,243
 Thanks
 19
 Thanked 46 Times in 45 Posts
Joint Variation
This one puzzles me. I thought I knew how to do that, but my answer didn't agree with the provided answer (no explanation, however). I can't justify the "correct" answer.
Let's see what others think.

20131002, 14:42 #2
 Join Date
 Dec 2009
 Location
 StEustache,QC,Canada
 Posts
 239
 Thanks
 10
 Thanked 21 Times in 20 Posts
Well, if it varies as the square of the wind velocity and the wind velocity triples then the force should be 9 times (3 squared) or 405 pounds, since the sail area is constant.
Of course, to some of us 405 pounds might be the cost
What was the "correct" answer?

20131002, 16:51 #3
 Join Date
 Jan 2001
 Location
 La Jolla, CA
 Posts
 1,243
 Thanks
 19
 Thanked 46 Times in 45 Posts
I read it as varying as the AREA OF THE SAIL and the SQUARE OF THE VELOCITY. While I agree that the square is 9, as you pointed out, I thought the 9 should be multiplied by the area of the sail. Yes, your answer was the one they said was correct. But I don't understand why you wouldn't multiply the 9 times the 50 (area of the sail).

20131003, 22:09 #4
 Join Date
 Aug 2010
 Location
 Pa, USA
 Posts
 2,192
 Thanks
 95
 Thanked 511 Times in 466 Posts
KW,
I would have done the same calculation as Jockmullin. If the wind velocity increases by a factor of 3 then the pounds would increase by a factor of 3 squared. I believe that you might have made the assumption that: sail size x wind velocity= the pressure on the sail. It is probably some intense formula that involves many variables such as the angle of the wind to the sail, resistance, direction of current, etc., however, if all of these factors are constant, then pounds would be directly proportional to wind velocity.
I am just surprised that it was not measures in something like pounds per square foot.
Not a sailor, more a landlubber.Last edited by Maudibe; 20131004 at 17:36.