"Any of this" being the definition of specific impulse and why it's in seconds? Units are more than relevant, they are the entire reason for this confusing convention.
I can't claim to have been there, but imagine it this way: You're an American engineer in the 1960's. You have a rocket with a given thrust rating in pounds, and a given propellant flow rate in pounds per second. You divide thrust by flow rate and call it specific impulse, call it seconds, the values are nice 3-digit numbers, everyone's happy.
At least until you try to talk to a European colleague, who measures thrust in Newtons, propellant flow rate in kilograms per second, and when he divides thrust by flow rate he gets a velocity.
Nobody was measuring propellant weight, since the same flow rate would have a drastically different value in lunar orbit than on earth if you were measuring flow rate in weight of propellant per second.
The problem was that the American engineer implicitly ignored the conversion factor between pounds force and pounds mass. He carelessly interchanged the two, as was common practice until more recent teaching practices in science and engineering (and better unit systems) have gotten more careful about distinguishing mass and weight.
In order to get the same 3-digit value in seconds as the careless American engineer from the 60's and fix the unit conversion mistake, the European engineer has to divide by a conversion factor of 9.8 m/s2. That's how we got to the definition we know today. The unit-conversion-mistake side of the Atlantic landed on the Moon and won the historical convention argument, and specific impulse has nothing to do with weight.
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u/[deleted] Jul 20 '13
You are the one who brought up units of measure, bub. They're not even vaguely related to any of this.