Sorcha's comment about the Board of Education in Kansas stole my thunder, but as an approximation that is understood to be an approximation, I don't think it's a horrible horrible thing, after all, that equation won't deal realistically with a skydiver at all, whose situation is more determined by his/her position in the air stream as he/she reaches terminal velocity, which means acceleration is zero due to a balance between acceleration due to gravity and wind resistance.

Amos, making the 'g' constant of gravity equivalent to acceleration is a relatively recent development known as Einstein's general theory of relativity.