How do you know the acceleration of a projectile is constant?

Question

Could it actually change

Answer 1

The acceleration of gravity is a constant, not the acceleration of cars or bullets unless they are in free fall.
g = 9.8 m/s/s, downward

It was learned in the previous part of this lesson that a free-falling object is an object which is falling under the sole influence of gravity. A free-falling object has an acceleration of 9.8 m/s/s, downward (on Earth).

Answer 2

It could change. It all depends on what forces are involved. If the object is falling it will accelerated constantly from gravity. However air friction will increase as it accelerates, slowing the acceleration until the two forces are in balance. Most theoretical physics questions ignore environmental concerns as much as possible.

Answer 3

It is not constant. It is constant for a short distance, say a bullet, then it will slow down and fall to the ground at its max distance. Air, wind and friction will slow it down. A bullet at its maximum range will start to fall to the ground and actually stop. If you were standing at the actual max range of that bullet it would gently land on your chest and not kill you.

Answer 4

The only way to know it is a constant is if there are no other outside forces affecting it.