Difference between a Parabola and Catenary?

I'm taking a math class online and I have to discuss Parabola's in real life. I want to talk about Telescopes and the Electromagnetic Spectrum but I want to make sure this is a parabola and not a catenary (like the St. Louis Arch). If this isn't a parabola, could you please explain to me how to tell the difference so I can choose correctly.Difference between a Parabola and Catenary?
This exact question was answered at web page below.

I know what you mean. they look very similar but they have different equations

and as you can see, the catenary is slightly flatter near the vertex.



http://mathforum.org/library/drmath/view鈥?/a>

Also, look at

http://en.wikipedia.org/wiki/Catenary



Discussing parabolas in real life suggests the subjects of gravity and projectiles.

Telescopes headlamps and torches - parabolic reflectors relate parallel beam to focus.

I think St. Louis Arch IS a parabola but GOOGLE it to check



How does the Electromagnetic Spectrum come into it ? Is it rainbows ?



Good luck.

Regards - Ian