Ugly confession time: I frequently confuse the concepts of "mass" and "weight."To which came the reply -- On earth the two concepts are essentially identical.
I couldn't let that stand, despite common usage. I.E., erroneous common usage.
Just because we end up using the two terms, mass and weight, interchangeably and even have an illegal conversion formula, doesn't mean they are the same thing.
And being the teacher, I had to share this to a wider audience.
And await the derisive comments on Facebook. (grin)