Catenary
Lesson notes
Overview
A hanging chain forms a cosh curve, not a parabola. Arches use the same shape upside down. This topic is rated beginner and is number 41 of 245 in Mathematics. Core ideas and first intuitions. No prior knowledge needed.
What you are seeing
The panel above shows a graph of the function. Each slider changes one parameter, so you can see exactly how the curve bends, shifts or stretches. The animation is drawn live from the model, so everything you see responds to the sliders. Press Space to pause, use Restart to replay from the start, and change the speed to slow down quick events.
In depth
The catenary is the shape taken by a flexible chain or cable hanging under its own weight from two supports. It looks like a parabola but is actually y = a·cosh(x/a), and Galileo’s belief that it was a parabola was disproved in the 17th century. Turned upside down it gives an ideal arch, because every part of it is in pure compression, which is why the Gateway Arch in St. Louis is shaped like a catenary.
The key idea, step by step
1. A hanging chain forms a cosh curve, not a parabola. 2. Arches use the same shape upside down.
Reading the relationship
The expression "y = a·cosh(x/a)" is a compact summary of the idea. It uses the symbols y, a, c, o, s, h; name what each one stands for before you start. Notice that it contains a ratio, so increasing the denominator makes the result smaller, and a trigonometric function, so the result repeats as the angle goes round. Then use the sliders to see how changing one quantity changes the others.
A guided exploration
1. Set every slider to its middle value and note the shape of the curve. 2. Move one slider at a time and describe whether the curve shifts, stretches or turns. 3. Find the value where the behaviour changes sharply, then connect it to the formula.
Try this
Start by only moving one slider at a time. Say aloud what you expect, then check.
Common pitfalls
A frequent slip is memorising the rule without the picture. If a result surprises you, sketch the graph or test a simple number by hand before trusting the algebra.
How it connects
It builds on “Spirograph Curves”, the topic before it in Mathematics. Once you are comfortable, continue with “Lissajous Knots”.
Why it matters
Mathematical ideas like this one are the language that physics, engineering, computing and statistics are written in.
Where you might use it
- Revising “Catenary” before a class, exam or certification
- Checking working on homework and exam questions by watching the graph respond
- Modelling growth, change and uncertainty in finance, data science and statistics
- Building the reasoning behind the algorithms and engineering tools people use every day
Frequently asked questions
What is Catenary?
A hanging chain forms a cosh curve, not a parabola. Arches use the same shape upside down. It is a beginner topic in Mathematics.
How do I use the Catenary simulation?
The panel at the top shows a graph of the function. Each slider changes one parameter, so you can see exactly how the curve bends, shifts or stretches. Move the sliders one at a time, then press Space to pause the animation and look closer.
What does the formula mean?
The expression y = a·cosh(x/a) packs the idea into symbols. Name each symbol first, then change one quantity with the sliders and see which others respond.
Who is this topic for?
Core ideas and first intuitions. No prior knowledge needed. If the quiz feels hard, reread the lesson notes and try the previous topic first.
What should I learn before this?
Start with “Spirograph Curves”, the previous topic in Mathematics. Each topic in a subject builds on the ones before it.
How do I track my progress?
Press “Mark as learned” on this page. Progress is stored only in this browser and is never sent anywhere. The Browse page can show topics you have learned or still need to learn.