Sigma, Epsilon, Desserts and Stiff Members

http://upload.wikimedia.org/wikipedia/commons/thumb/d/d5/Sigma_uc_lc.svg/800px-Sigma_uc_lc.svg.png

In engineering, stress is shown by the Greek letter sigma, the lower case “s”. Sigma looks a bit like a teapot. Stress is load (say, weight) divided by the area the load is applied to. Think of it as being like pressure. When subject to stress, materials respond by deforming a bit. Imagine applying a lot of weight to, say, a dessert ice cream bar standing on its end. You can see that given enough weight, the bar will scrunch down a bit. The length of the scrunching, the deformation, divided by the original length of the ice cream bar is called strain, which engineers show by the Greek letter epsilon, which looks like an “e”. I have no idea why strain is shown by the letter e, but I assume the letter “s” was already spoken for by sigma.

Generally, stress happens first, then strain. So when you say that you are feeling stressed, you are actually feeling the effects of stress; or you are strained. It is the strain that bends you out of shape on a bad day. By the way: the word “stressed” is “desserts” spelled backwards. (Thanks Carolyn K~ for that one!) Although you can do stress testing with ice cream bars if you want, engineers stress test metal, concrete, rock, soil, glass – just about everything but desserts. Well – maybe sweet engineers test desserts.

Stress is a big deal in engineering. Not only do we scribble teapot symbols on our notepads a lot, we have to work with it all the time. It is one of the main reasons that civil and structural engineers go to work: to work with stress. The folk who do the most work with stress are mechanical engineers and structural engineers. Civil engineers do a fair amount of work with stress too. (Electrical engineers don’t but they have their minds stressed with Imaginary Numbers). Structural engineers have to work out where the stress can be found in buildings and make sure that the various bits of the building like columns, and beams and the like, are up to the job. Engineers call those bits “members”. In buildings not all the members contribute: the highest stresses flow toward the members that can take the stress. We call those stiff members, because they do not deform/strain/scrunch too much. So: stiff members are very important.

We engineers work with stress so much it that it deforms us. Dr Chris H~, a dear colleague, just told me he was stressed. (That is why I am writing this post in the middle of my day. It is my gift to him.) Of course he is stressed: stress always flows to stiff members. He is a senior professional in the office. In my experience, work and worry always seems to flow, pile up on, load those folk who can, and have to, handle it -just like stiff members in a building. Without a few stiff members the rest of us would have to work harder.

Now he knows that, perhaps he should leave early for the day and go stess test an ice cream by eating it. (He’s a sweet guy…).

About Ed Medley

Ed Medley has been on a random walk for over 50 years. Many scribbles and snapshots at this site are from his vagabond transits; others are from his decades of international experience in geological and geotechnical engineering, academia, and mineral exploration prospecting.
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1 Response to Sigma, Epsilon, Desserts and Stiff Members

  1. Pingback: Good Soil, Bad Dirt | Ed Medley

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