An elementary school teacher wanted to teach his students about the density of different objects. His father worked in a machine shop with a variety of materials--wood, steel, aluminum, and titanium. He asked his father to make a cube which measured 1.000 cm on each side. He agreed. A month later, the father brought a beautiful shining cube of steel to his son’s classroom. The sides of the cube were mirror smooth and the edges were razor sharp. It looked beautiful, like a work of art. The father said to his son, “This cube cost $500. Since you are my son and a teacher, the company is willing to donate it to you. If you want another cube, though, you will have to pay for it yourself.” Why did it cost so much to create the steel cube for the teacher?