Remembering to Use the Right Units

Over the weekend I have been tutoring Astronomy. It is a topic that is quite a passion for me. While working on some formulas for calculating the escape velocity of various planets I came across a basic mistake that can easy throw off your answer. The mistake was not using the right units. Surprisingly this mistake is more common than you might think. NASA actually lost a Mars probe once because an engineer used inches instead centimeters. I thought this needed some attention seeing that I even initially did not notice the mistake.

Most of the time distance will be measured in either Miles or Kilometers. These two measurements are from different systems. Kilometers is part of the metric system, which you will probably only encounter in your science class (or while traveling). Luckily it is really easy to change one type of measurement to the other.

In order to change miles to Kilometers you multiply the amount of Miles by 1.6.

In order to change Kilometers to Miles you multiply the amount of Kilometers by 0.8.

Another very common conversion is Kilometers to Meters. This one is really easy to remember.

In order to change Kilometers to Meters you multiply the amount of Kilometers by 1,000.

In order to change meters to Kilometers you divide the amount of Meters by 1,000.

Keep in mind what units you are using and you’ll be trouble free.


Your point about keeping track of units is very important! I have also seen teachers/professor grade down if the unit is not declared when the number is recorded (e.g., If one answers 1 mile + 1 mile = 2, not 2 miles), and when charts use a measurement unit that is not labeled (e.g., not labeling the y axis "Number of Miles" and just having the reader assume the units). As you pointed out, not only could a person get a poor grade, but s/he could even lose a Mars probe!


Ivan N.

Public Speaking, Math and Social Sciences

50+ hours
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