Even though the bones are very hard, the two bones that form a joint do not cause friction, except in the elderly. which is an appropriate justification for the smooth movements of these bones? synovial fluid, which is present in the space between the joints, acts as a lubricant, thus avoiding friction of the two bones forming a joint. cartilaginous disc, which is present in the space between the joints, acts as a lubricant, thus avoiding friction of the two bones forming a joint. acetylcholine, which is present in the space between the joints, acts as a lubricant, thus avoiding friction of the two bones forming a joint. nextreset