Mass, volume, and density are concepts you teach over and over again during the school year in many different ways. Help students understand the relationships between mass, volume and density with our Equal Mass Kit. Five cylindrical objects, made of different materials with differing lengths, all have exactly the same mass and radius. Thus, density is inversely proportional to length. Contains five cylinders: brass, aluminum, nylon, PVC, and polyethylene-all 1/2" in diameter and 15 g in mass. Classroom set includes 15 sets of materials, enough for 30 students working in pairs.