The lubrication of bone joints is a subject of ongoing medical research. two bones connected at a joint do not touch. the bones are covered in articular cartilage, and are surrounded by lubricating synovial fluid. rheumatoid arthritis results in overproduction of synovial fluid, swollen joints, and difficult and painful movement. other joint disorders degrade the synovial fluid, directly increasing the friction between the bones, resulting in painful motion.

part a

to measure the effective coefficient of friction in a bone joint, a healthy joint (and its immediate surroundings) can be removed from a fresh cadaver. the joint is inverted, and a weight is used to apply a downward force