How do you replace a rectangular aluminum bar with an equivalent aluminum rectangular tube?

Answer 1

I assume you're referencing the mathematical problem of "squaring the circle." Engineers use increasingly precise values of pi (more digits) to estimate the volume/area required; as the requirement for precision increases, more digits are used.

For example, if an engineer needed to replace a rectangular pipe with a cylindrical one (and maintain the same volume), he would determine how precise the new fitting had to be to maintain functionality, and then use an appropriate value for pi.

(In a very loose comparison, perhaps the value 3.14 would be used for an outdoor water system, and 3.1415927 would be used for a life-support system on the International Space Station.)

(I'm a physics undergrad at the University of Utah.)