Final answer:
An object falling off a building is acted upon by gravity, causing it to accelerate towards the Earth, and by air resistance, which opposes its downward motion.
Step-by-step explanation:
When an object falls off a building, two main forces act upon it: gravity and air resistance. The force of gravity causes the object to accelerate towards the Earth's center at an average acceleration due to gravity (g) of 9.81 m/s². Air resistance, on the other hand, acts in the direction opposite to the motion of the falling object and varies depending on the object's shape and surface area. Larger surface areas experience more air resistance, which can slow down the object's fall.
According to Newton's second law, a net force causes an object to accelerate. In the case of a falling object where air resistance is negligible, the gravitational force is the net force acting on the object. However, when considering real-world scenarios, air resistance cannot be ignored, and it acts to reduce the acceleration of the object as it falls.