How to know which units to use?

A lot of formulas say stuff like Force=Mass(Acceleration^2). And usually they tell you that the force is measured in newtons, the mass in kilograms and the Acceleration in Meters per second. But a lot of times, they simply do not.

And you get a way different result if you say use grams instead of kilograms. Or kilometers/s instead of meters/s.

So is there like a list of which standardized units are used where? Is a formula always going to assume kilograms and meters? And even if so what about Moles, Candelas, Amperes and Hectares or whatever. Which suffixes are the right ones to use?

Also why are formulas always abbreviated to just the letters? I've often tried to look up how something is measured. Only to be hit with a bunch of variables but with no glossary explaining what those variables were.

Its like saying "Energy equals 'M' 'C' squared" but never explaining that 'M' is mass and 'C' is the speed of light.

 

units could be converted:
Converting between units can be done through the use of conversion factors or specific conversion formulas.

here is a good link (videos included) about units:

https://courses.lumenlearning.com/boundless-physics/chapter/units/

https://www.unitconverters.net/

 

Well, first, NO formula says "Force=Mass(Acceleration^2)"! Force= Mass(Acceleration) without the square. You probably mistakenly took the square from the fact that acceleration itself is "meters per second squared".

As MathLover1 said, you are free to use whatever units you want, as long as you are consistent. You can measure distance in meters, centimeters, kilometers, inches, feet, yards, or miles. Acceleration can be in "meters per second squared" or "miles per hour squared".

Force can be in "Newtons" or "dynes" or "pounds". In science we use the metric system because it is simpler- 100 cm in a meter, 1000 meters in a kilometer rather than 12 inches in a foot, 3 feet in a yard, 5280 feet (1760 yards) in a mile. And typically use the "MKS" (meters, kilograms, seconds) units rather than the "cgs"(centimeters, grams, seconds) system, because it fits what we are talking about better. (But might use "cgs" for a tabletop lab.)

The Newton, a unit of force, is defined as "one kilogram meter per second squared", again "mass(acceleration)", the force necessary to accelerate a one kilogram mass at one meter per second per second, while the dyne is defined as "one gram per second per second". Since a kilogram is 1000 grams (the prefix "kilo" is from the Latin for "1000") a Newton force is a thousand times as strong as a dyne force.

In addition to the confusing units, the English system, in every day, non-science talk uses the word "pound" for both force and mass (on the surface of the earth weight (a force) is proportional to mass). Scientists and Engineers have to specify "pound-mass" or sometimes the "slug" for mass.

 

Impressive.