Gravitational Acceleration $g$ How to determine sign of $g$?   It is said that we take  it negative if any body is in upward motion. So why we don't take it positive when we observe downward motion.It is very confusing.
Sign of the vector (especially $g$) while calculating I'm a high school student and I'm studying Newton's second Law. While my teacher is calculating a net force of an object he always treat all vectors as positive numbers. I think what he meant is the magnitude of the vector which is always positive, but the problem is that he didn't use the magnitude symbol, for example like $||Fg||$. He said the acceleration due to gravity , g, is positive, but shouldn't it be negative since it is pointing down. This also cause a problem: every time when I calculate the net force I can't add all forces together, instead I need to choose to use minus sign when the vector is pointing down. So in general which way is correct?
How is double negation interpreted in English? In my native language, double negations "cancel out". I have been trying to learn English using movies and such things, but double negation confuses me. I see instances when double negation cancels out, and some when they do not.  For example, "I haven't got no money" is interpreted as "I have no money." "There wasn't anyone who didn't enjoy the party" is interpreted as "Everyone enjoyed the party."  Is this context dependent? If so, how does one decide which interpretation is correct?