Suspended Rope Trick

What is the shape of a suspended rope? Is there some function that describes it?

Answer: it’s the cosh curve!

Presentation Suggestions:
This may be seen quite dramatically by putting up a transparency of the catenary

y = cosh x

and suspending a rope in front of the transparency projection so that the rope shadow can be compared!

Now, someone may object and say that the curve of x2 will also give a good approximation. If they do this, you can talk about how the of cosh begins with a quadratic 1 + x2/2, so it is not surprising!

The Math Behind the Fact:
 and modeling are useful here: by breaking the rope into lots of little chunks, and modeling the forces on each chunk, one can obtain a differential equation whose solution is the cosh curve.

How to Cite this Page: 
Su, Francis E., et al. “Suspended Rope Trick.” Math Fun Facts. <>.

Fun Fact suggested by:
Michael Moody

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