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Bench Talk for Design Engineers

Bench Talk

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Bench Talk for Design Engineers | The Official Blog of Mouser Electronics


Unique Units and Brilliant Reductions Caroline Storm Westenhover

I love units of measurement: how you can multiply and divide unit Y by unit X and get unit J or W. If you know the units you want, you can look at the information you have and figure out how to get the answer you want just by cancelling units or introducing new ones. Clearly, this is limited to the realm where I am given enough information to solve a problem without experimentation. Still, the wonderful fact remains that if someone asks me a simple physics question, I can often answer it based solely upon the units involved and the basic units those break down into. Or conversely, I can do a quick error check by making sure the units equal each other. Obviously there are limits to this, or Maxwell’s equations would not be so impressive.

 

The other day someone asked me how much energy it would take to push a kilogram. This is an impossible question to answer without some additional information. A kilogram of what against what surface? How far do you plan to push it? I was able to explain these problems to a first semester physics student by sitting down and explaining that a joule is equal to a kilogram meter squared per second squared (Kg-m2/s2) or a Newton meter (N-m). Therefore, if you knew the frictional force between the two, the result is Newtons and if you knew the distance, the result is the Newton meter or the joule.

 

Figure 1: The U.S. national prototype kilogram (K20) stored at the US National Institute of Standards and Technology. (Image source: en.wikipedia.org)

Units paired with basic mathematical concepts let you solve problems that are different from the examples presented in class. You are not stuck to the block sliding down a ramp. Those problems are stepping stones to solving any number of problems using those same concepts. This is why I find the kilogram project, the attempt to get the kilogram paired with a law of nature, so important. Having such a fundamental unit based on an actual object takes something that is amazing in the abstract and makes it boringly concrete. How much better to explain a unit of mass versus force by explaining that a kilogram is based on a certain number of atoms, or that it is based on a certain number of quantum seconds per cubic meter? Granted, the second definition is non-intuitive, but it remains unchanging across the years with respect to other constants in nature. Instead of ending at the international prototype kilogram, which can be lost to the ages, it relates back to unchanging physical properties. It weaves our scientific progress into the very fabric of nature. Rather than standing out in relief against it, our knowledge is inseparable from the physical laws and constants that define our world.



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My name is Caroline Storm Westenhover. I am a Senior Electrical Engineering student at the University of Texas at Arlington. I am the third of seven children. I enjoy collecting ideas and theories and most enjoy when they come together to present a bigger picture as a whole. Perhaps that is why I like physics and engineering.  My biggest dream is to become an astronaut.


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