Final answer:
Gravity causes all objects to fall with the same acceleration when air resistance is negligible. A 500 lb weight dropped from a window will hit the ground with constant acceleration, and this occurs because gravity pulls with the same acceleration on all masses.
Step-by-step explanation:
Gravity is the force that will cause a 500 lb weight to accelerate towards Earth when it is dropped from a window of a tall building. When we ignore air resistance, the weight will hit the ground below with a constant acceleration, independent of its mass. This phenomenon occurs because gravity pulls on all objects with the same acceleration. Observing that all objects fall with the same acceleration in the absence of air resistance can be explained by the fact that gravity acts equally on all masses. This was a groundbreaking discovery by Galileo, and it contradicts many people's intuition that a heavier object should fall faster. In reality, given the same height, both heavy and light objects hit the ground at the same time. You would tell your buddy that what you observed happens because gravity pulls on everything with the same acceleration.