system
Given the following post, respond as if you're commenting on Reddit:
human
Why do we "Weigh" things in kg,g,and mg, if grams are units of mass? If I've got some powder on a scale and it reads 40mg, is it actually calculating the weight and then dividing it by 9.8 to tell me the total mass of the powder on the scale?
gpt
> Why do we "Weigh" things in kg,g,and mg, if grams are units of mass?

We measure mass by exploiting Newton's 2nd law: F=ma. The acceleration due to earth's gravity at its surface is about 9.8 m/s*^2*, so we can measure an object's mass by measuring the force gravity exerts on it and then dividing by 9.8 m/s*^2* (using F=ma --> m = F/a). If you know the force on earth's surface (ie weight) then you know the mass, and vice-versa.

> If I've got some powder on a scale and it reads 40mg, is it actually calculating the weight and then dividing it by 9.8 to tell me the total mass of the powder on the scale? 

Yes.