Example 2.  Find the equation of the parabola that goes through the origin and the point [Graphics:Images/CatenaryMod_gr_129.gif].  Compare the parabola solution with the catenary solution.
Solution 2.

[Graphics:../Images/CatenaryMod_gr_130.gif]



[Graphics:../Images/CatenaryMod_gr_131.gif]

[Graphics:../Images/CatenaryMod_gr_132.gif]

[Graphics:../Images/CatenaryMod_gr_133.gif]

[Graphics:../Images/CatenaryMod_gr_134.gif]

[Graphics:../Images/CatenaryMod_gr_135.gif]

[Graphics:../Images/CatenaryMod_gr_136.gif]


Plot the parabola solution.

[Graphics:../Images/CatenaryMod_gr_137.gif]


[Graphics:../Images/CatenaryMod_gr_138.gif]

[Graphics:../Images/CatenaryMod_gr_139.gif]

[Graphics:../Images/CatenaryMod_gr_140.gif]

[Graphics:../Images/CatenaryMod_gr_141.gif]


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

[Graphics:../Images/CatenaryMod_gr_142.gif]

[Graphics:../Images/CatenaryMod_gr_143.gif]



[Graphics:../Images/CatenaryMod_gr_144.gif]

[Graphics:../Images/CatenaryMod_gr_145.gif]

[Graphics:../Images/CatenaryMod_gr_146.gif]


The length of the parabola is easily computed using Mathematica's built in [Graphics:../Images/CatenaryMod_gr_147.gif] subroutine.

[Graphics:../Images/CatenaryMod_gr_148.gif]



[Graphics:../Images/CatenaryMod_gr_149.gif]

[Graphics:../Images/CatenaryMod_gr_150.gif]


The length of the parabola could be computed analytically.

[Graphics:../Images/CatenaryMod_gr_151.gif]



[Graphics:../Images/CatenaryMod_gr_152.gif]

[Graphics:../Images/CatenaryMod_gr_153.gif]

[Graphics:../Images/CatenaryMod_gr_154.gif]

[Graphics:../Images/CatenaryMod_gr_155.gif]

[Graphics:../Images/CatenaryMod_gr_156.gif]

[Graphics:../Images/CatenaryMod_gr_157.gif]

[Graphics:../Images/CatenaryMod_gr_158.gif]

[Graphics:../Images/CatenaryMod_gr_159.gif]

[Graphics:../Images/CatenaryMod_gr_160.gif]


Notice that there is a difference between the length of the catenary and the length of the parabola.

[Graphics:../Images/CatenaryMod_gr_161.gif]


[Graphics:../Images/CatenaryMod_gr_162.gif]

[Graphics:../Images/CatenaryMod_gr_163.gif]



[Graphics:../Images/CatenaryMod_gr_164.gif]


[Graphics:../Images/CatenaryMod_gr_165.gif]

[Graphics:../Images/CatenaryMod_gr_166.gif]

[Graphics:../Images/CatenaryMod_gr_167.gif]


We could plot the difference.  This is just for fun!

[Graphics:../Images/CatenaryMod_gr_168.gif]


[Graphics:../Images/CatenaryMod_gr_169.gif]

[Graphics:../Images/CatenaryMod_gr_170.gif]

What is the maximum difference in the height of the catenary and parabola?

[Graphics:../Images/CatenaryMod_gr_171.gif]


[Graphics:../Images/CatenaryMod_gr_172.gif]

[Graphics:../Images/CatenaryMod_gr_173.gif]

If the unit of length was feet, what is the maximum difference in the height of the catenary and parabola in inches?

 

[Graphics:../Images/CatenaryMod_gr_174.gif]

[Graphics:../Images/CatenaryMod_gr_175.gif]

In your home if the error made in construction was  1.7 inches  off in  6 feet  of height, would you have a concern ?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(c) John H. Mathews 2004