Kathy had a heavy metal ball and Rich had a light wooden ball. They dropped the balls from the same height. They were surprised to discover that the two balls reached the ground at the same time. This is what they said after the balls landed:

Kathy: "The force of gravity must be acting the same on both balls."

Rich: "I don’t agree. The metal ball weighs more, so the force of gravity is more on the heavier ball."