As the human body has over 200 different bones, they need to be joined
together to form the skeleton. The bones are joined together by joints, which
allow them to move.
The synovial joint
Some joints within the body contain a fluid called, synovial fluid. This fluid
helps to reduce the friction between two different bones. The fluid is aided
by cartilage, which surrounds the ends of the bones preventing direct
contact between the two bones. Without these mechanisms the bone
would eventually wear away causing a lot of pain.