When a ball is dropped it is easy to see that earth exerts a force on it. why cant you tell that the ball exerts a force on it. why can't you tell the ball exerts a force on Earth

Because the distance that each object moves is in inverse proportion to their masses. That means the earth moves such a little tiny tiny tiny bit that you can't see it. but you're right. It's important to understand that when you drop a ball the ball and the earth both move toward each other.