Question

Which statement best explains why a paper airplane eventually falls to the ground?
A. The unbalanced forces of air resistance and gravity slow the airplane and pull it down.
B. The force from throwing the airplane loses strength as the airplane moves.
C. Inertia slows the airplane and pulls it down.
D. Inertia prevents new forces from acting on the airplane to keep it up.

Answer 1

A. The unbalanced forces of air resistance and gravity slow the airplane and pull it down.

Gravity constantly pulls the plane downward. As it flies, air resistance (and imperfect lift) reduces its forward speed and lift, so the upward forces become smaller than gravity. That net (unbalanced) force causes the plane to decelerate and descend.