Units are extremely important in science and engineering. It’s one thing that you’ll find professors stressing over and over again in the early engineering classes of aerospace engineering. And for good reason. When I TAed Intro to Aerospace Engineering, it’s something I found students consistently messing up. A solid understanding of units can get you really far in engineering and science.

It’s important to introduce the two types of units seen in American engineering: English units and metric units. You might here metric units also referred to as SI units, which comes from the French for “the international system”. Metric units are generally loved and adored my engineers and scientists, but unfortunately, most American groups operate in English units. English units can be very difficult to work with. Lucky for me, the space industry works mostly in metric. Woohoo!

So in the table below I’ll list a parameter like time, length, force, velocity, etc, and then list the appropriate unit for the two different unit systems. Also, you may say “wait! But length can be measured in feet, inches, miles, and so many more!” True, but I’m listing the generally accepted base unit. Sometimes the “base” unit is harder to determine for English units, but for metric they’re accepted for the most part to be seconds, meters, and kilograms. You can make any other unit from those units. It’s actually really amazing.

This list doesn’t even come close to being comprehensive. I’ll add to it as we discuss more.

Parameter English Metric (SI)
time seconds (s) seconds (s)
length feet (ft) meters (m)
mass pound-mass (lbm) or slugs kilograms (kg)
force pound-force (lbf) Newton (N)
velocity feet per second (ft/s) meters per second (m/s)
acceleration feet per second squared (ft/s2) meters per second squared (m/s2)

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