A lever is a simple machine that magnifies speed of movement or force.
Spongy bone occurs at the ends of long bones and is less dense than compact bone.
Yellow marrow , at the center, is used to store fats. The minerals calcium and phosphorus give bone its hardness, strength, and rigidity to resist compressive forces. The collagen fibers impart flexibility. Osteoblasts , the cells responsible for making bone, maintain the balance of calcium in the blood and bone. When this balance is disrupted, as in osteoporosis , the removal of bone exceeds its production, making bone thin and brittle, thus more easily fractured.