A recent post by Rhett Allain of Dot.Physics fame has drawn a number of negative comments and I wanted to address the concerns that came up. The post is titled Does the Slope of a Pyramid Really Matter? and the question asked is what is the maximum height for a pyramid based on the strength of the rock used to build the pyramids. The back of the envelope calculations showed the maximum height could be over a kilometer high so the compressive strength of rock is not a limiting factor and wouldn’t explain why the Bent Pyramid is bent.

Several of the commenters were very negative about the fact that the post didn’t explain why the Bent Pyramid is bent. Some felt that ” [i]f you just start making stuff up along the way (“compressive strength of limestone=60MPa so let’s call it 80MPa”) your analysis looses all credibility.” I understand their point, but I think the commenters are not familiar with the blog in question.

Here is what I have to say in defense of the post on Dot.Physics (and as an explanation of my philosophy for my own blog): The primary goal of this blog post is to show how a scientist might break an otherwise fairly complex problem down into something that is easy to understand. It’s goal is not to create new knowledge, or to definitively prove or disprove something, merely to show how you might approach it. To put it another way, the primary goal is to act as a mental scaffold for students of physics. You don’t need a PhD in physics to complete any of these calculations, only an introductory course in physics and curiosity.

Back-of-the-envelope calculations are one of the most used tools in a physicists tool box. During my entire graduate education I can probably count the number of times I broke out differential equations to solve a problem. More often than not I could rely on a quick chicken-scratch equation to tell me what I needed to know. I really only needed to bring out the big guns when I needed to publish something.

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