Example 1.  Find the catenary that goes through the origin and also passes through the two points  with  a = 10  and b = 6.

Solution 1.

[Graphics:../Images/CatenaryMod_gr_91.gif]

[Graphics:../Images/CatenaryMod_gr_92.gif]

 

 

Enter the formula for the catenary and determine the constant [Graphics:../Images/CatenaryMod_gr_93.gif].  

[Graphics:../Images/CatenaryMod_gr_94.gif]



[Graphics:../Images/CatenaryMod_gr_95.gif]

[Graphics:../Images/CatenaryMod_gr_96.gif]

[Graphics:../Images/CatenaryMod_gr_97.gif]

[Graphics:../Images/CatenaryMod_gr_98.gif]

[Graphics:../Images/CatenaryMod_gr_99.gif]

[Graphics:../Images/CatenaryMod_gr_100.gif]

[Graphics:../Images/CatenaryMod_gr_101.gif]

[Graphics:../Images/CatenaryMod_gr_102.gif]

[Graphics:../Images/CatenaryMod_gr_103.gif]

[Graphics:../Images/CatenaryMod_gr_104.gif]


Plot this solution.

[Graphics:../Images/CatenaryMod_gr_105.gif]


[Graphics:../Images/CatenaryMod_gr_106.gif]

[Graphics:../Images/CatenaryMod_gr_107.gif]

[Graphics:../Images/CatenaryMod_gr_108.gif]

[Graphics:../Images/CatenaryMod_gr_109.gif]


The length of the catenary can be approximated numerically by using Simpson's rule.

[Graphics:../Images/CatenaryMod_gr_110.gif]
[Graphics:../Images/CatenaryMod_gr_111.gif]



[Graphics:../Images/CatenaryMod_gr_112.gif]

[Graphics:../Images/CatenaryMod_gr_113.gif]

[Graphics:../Images/CatenaryMod_gr_114.gif]


The length of the catenary is easily computed using Mathematica's built in [Graphics:../Images/CatenaryMod_gr_115.gif] subroutine.

[Graphics:../Images/CatenaryMod_gr_116.gif]


[Graphics:../Images/CatenaryMod_gr_117.gif]

[Graphics:../Images/CatenaryMod_gr_118.gif]

Remark. This could also be computed analytically.  Recall that

    [Graphics:../Images/CatenaryMod_gr_119.gif][Graphics:../Images/CatenaryMod_gr_120.gif][Graphics:../Images/CatenaryMod_gr_121.gif][Graphics:../Images/CatenaryMod_gr_122.gif].
    
Caution.  If you use [Graphics:../Images/CatenaryMod_gr_123.gif] then Mathematica will go into it's "special function" mode of operation and you will get Elliptic functions.

The formula Mathematica produces for [Graphics:../Images/CatenaryMod_gr_124.gif] will involve functions studied in first year calculus.

The following definite integral works.

 

[Graphics:../Images/CatenaryMod_gr_125.gif]

[Graphics:../Images/CatenaryMod_gr_126.gif]

Or you could use the formula

 

[Graphics:../Images/CatenaryMod_gr_127.gif]

[Graphics:../Images/CatenaryMod_gr_128.gif]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(c) John H. Mathews 2004