Tommy had a ball and a long plank at home. He put the ball on the plank and let it go. The ball rolled down slowly. "Try to make the plank higher," his mom said.

Tommy lifted one side of the plank. The ball rolled faster now. "Wow! The ball goes fast when the plank is high," Tommy said with a big smile.

His mom told him, "The ball moves because of gravity. It pulls the ball down the plank." Tommy liked learning this with his mom while playing. It was a fun day at home.