Final answer:
The main force acting on an object during free fall is gravity, as it is the only force causing acceleration towards Earth's center.
Step-by-step explanation:
The main force acting on an object undergoing free fall is gravity. This is because the only net external force acting on an object in free-fall is its weight, which is a measure of the gravitational force between the object and Earth. While other forces such as magnetism, normal force, and electromagnetism play important roles in various interactions, during free fall, gravity is the sole force causing the acceleration of the object towards the center of the Earth.