The most common and most likely answer to this crossword clue is the 9 plus 7 letter word CENTER OF GRAVITY
I've seen this crossword clue in The Guardian
C
E
N
T
E
R
�
�
O
F
G
R
A
V
I
T
Y
Buddy explains!
The straight part
We know that "In America, where an attractive force may be said to act" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case in america, where an attractive force may be said to act = center of gravity.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.