frozen physics lesson Last winter, Warren Christensen, an assistant professor of physics at NDSU, built a backyard igloo with his friend, Matt Brunsvold, for their boys. They used about 1,100 ice blocks made by filling empty milk cartons with food coloring and water. They then used slushy snow as mortar, and the igloo quickly fused into one solid block of ice. They started in mid-December and finished in mid-January. It lasted about two months. The structural integrity of a dome is extremely strong, and four adults could stand on it with no damage. Science!