# Physics Skills Mini-Lessons: What are units?

The unit of measurement of a quantity always needs to be noted when taking measurements, performing calculations, and reporting answers. In physics class, we immediately start using the term "units" but what does it mean? Where did measurement systems originate? What system is used in your country? What if you need to convert between measurement systems? Why in the world doesn't the entire world use the same system? The two mini-lessons below will start to expose you to some of these answers.

The first mini-lesson focuses on the two main measurement systems used in the world - SystÃ¨me International (SI) or the Metric System and the US Customary System. The differences between these systems is mentioned, as well as how to convert from one system of measurement to another using dimensional analysis. If you live within the United States, you are more than likely going to need to switch between systems based on your area of study.
If you are like me and wondering why the United States has not converted to the metric system yet, while the rest of the world has, check out this __YouTube Video__ from the Today I Found Out channel. It thoroughly summarizes the history of measurement systems as well as listing pros and cons of the transition to the metric system for the United States. What to hear my opinion on the matter? Visit __The Finding Physics Podcast__ later this week where I challenge the US to make one more attempt at true metrication.

The second mini-lesson demonstrates how units balance on either side of an equation. This concept is helpful for many reasons. First, students can see that all common measurements (such as length) in a problem must all be in the same units to process calculations. This will often require a conversion prior to doing a calculation. Second, this introduces the concept of derived units being comprised of fundamental units. (Yes, I am only referencing the metric system now!) Third, analyzing the units in an equation could help you determine the units for a constant in the equation. Fourth, if you analyze the units, it may unveil that you wrote down the equation incorrectly! (The later happens more often than students like to admit!)

Want more practice converting between measurement systems using dimensional analysis or analyzing the units in an equation? Then sign up for the __Physics Skills Summer Series__ or other workshops including this content. Want one-on-one attention? Then sign up for a __tutoring session__ that focuses on units.