, empirical?
, or that
?
or 
for
?
, why is the density of the medium associated with the quadratic drag coefficient 
, and the cross-sectional area of the object with the linear coefficient 
?
-axis as increasing downwards for projectile motion?
direction decided? In the lecture the -components of 
and 
should be the same (both down) but we write them opposite in
. Why?
, but why do we write it like this?
? Seems unnecessary.
?
from? How do you understand this expression intuitively?
from 
?
. Do we have to know them for Chapter 2?