Why is the gravitational acceleration g the same for a heavy and a light ball?

Good observation, and the answer is no. When you drop an object, the force pulling it down is its weight, which is mass times g. By Newton's second law, acceleration equals force divided by mass. So acceleration = (m × g) / m, and the mass cancels out, leaving just g. This means every object, heavy or light, falls with the same acceleration of about 9.8 m/s² when air resistance is ignored. The heavier stone is pulled by a larger force, but it also needs a larger force to accelerate because it has more mass, so the two effects balance. In real life a feather falls slower only because of air resistance, not gravity. In a vacuum, a feather and a coin land together.