A ball is thrown downward with an initial velocity of 3.8 m/s. What is its acceleration? a) 0 m/s/s
b) 9.81 m/s/s
c) 0 m/s
d) 9.81 m/s
e) -9.81 m/s
f) -9.81 m/s/s

Efficiency is an act of doing something

If there was no gravity then their would be no downword force on the football to have it return the the grownd, and if there was no friction (mainly air friction) then there would be no opposing force the stop the ball from moving through the air allowing the ball to travle ∞.