# A sphere, a simple object?

In this video, the woman says that a sphere is a pretty simple object. What intrigues me is the use of a sphere for such a calculation. First of all, the sphere wouldn't be perfect as a perfect sphere doesn't exist in nature (first source of imprecision). Second, one will have to use π for calculating the volume. As π is irrational, one will have to use an approximation for it (second source imprecision). So why not using a simple cube? The shape would be closer to a cube due it's harder to make a sphere and it's volume would be calculated more precisely. Why they choose to do this calculation using a sphere?

• Making a perfect right angle is harder than making a perfect circle. Apr 14, 2013 at 18:17
• Really? I always thought that a perfect circle was the most difficult shape to make. Apr 14, 2013 at 18:28
• Also, you're right that truly perfect spheres don't exist in nature. But, what's a greater source of error/imprecision in measurements of the figure of the Earth: using an approximation of Pi accurate only to 40 significant figures, or modeling the Earth as a simple cube? Apr 14, 2013 at 18:28
• π is not really a source of imprecision. It can be calculated to any arbitrary procision. A million digits for example. Apr 14, 2013 at 18:31
• Apr 14, 2013 at 18:31

You're right that $\pi$ can only be approximated. Still, we can use the maximum approximations as possible and we would - because, it's gonna be defined under the SI.