A triangular peg in a circular hole

A friend recently asked me a puzzle.

The engineers at NASA needed to verify that a fuel storage unit had a circular cross-section. They measured the width of the cross-section in all directions and concluded that the cross-section is circular. Were the engineers correct.

I thought that they were. A 2D object with constant width in all directions ought to be a circle. Right? I was wrong and here is a simple counterexample.

Take an equilateral triangle, and from each corner draw an arc connecting the other two corners.


All widths are equals, but this is clearly not a circle. Maybe the NASA engineers should have also checked if the circumference equals πd


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s