Scenario: The Elevator Test. Step 1: You are in a windowless elevator on Earth. You hold a ball. Step 2: You let go of the ball. It hits the floor in 1 second. Step 3: Now, take that same elevator into deep space. Step 4: A giant hand starts pulling the elevator upward with a specific force (acceleration). Step 5: You let go of the ball again. Because the elevator is accelerating upward, the floor rushes up to catch the ball in exactly 1 second. Result: Because the ball 'fell' the same way in both places, gravity and acceleration are equivalent.