Three things they should have taught in Engineering 101, Part 1: Units count!

Darren Ashby -January 30, 2013

Note: The following is adapted from the book "Electrical Engineering 101, Third Edition" by Darren Ashby (Newnes).

Do you remember your engineering introductory course? At most, I’ll venture that you are not sure you even had a 101 course. It’s likely that you did and, like the course I had, it really didn’t amount to much. In fact, I don’t remember anything except that it was supposed to be an "introduction to engineering."

Much later in my senior year and shortly after I graduated, I learned some very useful general engineering methodologies. They are so beneficial that I sincerely wish they had taught these three things from the beginning of my coursework. In fact, it is my belief that this is basic, basic knowledge that any aspiring engineer should be required to know.

I promise that by using these in your day-to-day challenges you will be more successful and, besides that, everyone you work with will think you are a genius. If you are a student reading this, you will be amazed at how many problems you can solve with these skills. They are the fundamental building blocks for what is to come.

This is a skill that one of my favorite teachers drilled into me during my senior year. Until I understood unit math, I forced myself to memorize hundreds of equations just to pass tests. After applying this skill I found that, with just a few equations and a little algebra, you can solve nearly any problem.

This was definitely an "a-ha" moment for me. Suddenly the world made sense. Remember those dreaded story problems that you had to do in physics? Using unit math, those problems become a breeze; you can do them without even breaking a sweat.

Unit Math
With this process the units that the quantities are in become very important. You don’t just toss them aside because you can’t put them in your calculator. In fact, you figure out the units you want in your answer and then work the problem backward to figure out what you need to solve it. You do all this before you do anything with the numbers at all. This basic concept was taught way back in algebra class, but no one told you to do it with units. Let’s look at a very simple example.

When all the units that can be removed are gone, what you are left with is 60 mph, which is the correct answer. Now, you might be saying to yourself that was easy. You are right! That is the point after all - we want to make it easier. If you follow this basic format, most of the "story problems" you encounter every day will bow effortlessly to your machinations.

Another excellent place to use this technique is for solution verification. If the answer doesn’t come out in the right units, most likely something was wrong in your calculation. I always put units on the numbers and equations I use in MathCad (a tool no engineer should be without). That way when you see the correct units at the end of your work, it confirms that the equations are set up properly. (The nice thing is that MathCad automatically handles the conversions that are often needed.)

So, whenever you come upon a question that seems to have a whole pile of data and you have no idea where to begin, first figure out which units you want the answer in. Then shape that pile of data until the units match the units needed for the answer.

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