The arrow flies across the field, two forces act on the arrow while its in the air. air resistance acts in the opposite direction to the movement and gravity acts downwards. these two forces cannot balance each other, even when they are the same size. why is

Because gravity is acting straight down. It does not act side to side. On the other hand, air resistance acts (in this case) only side to side, in the opposite direction of the movement. Even if the two are the same size, they are not acting in the opposite direction of each other, so they do not "balance each other out," i.e., do not stop each other.

Oblate

The return of the wolf to yellowstone national park will probably affect the bird population to some degree, not significantly. while wolves will hunt birds when necessary, they prefer to hunt larger prey. the bird population will most likely only be affected when hunting is scarce for the wolves. birds of prey will also probably not be affected as much as other birds who spend more time on the ground hunting for food as the tend to spend more time in the air or in trees since they do not need to stay on the ground for long due to the nature of the way they hunt.