Friction plays an important role in everyday life—contrary to what one might intuitively think. Without friction, movement on Earth would be impossible, as both walking and driving rely on transferring force to the ground through friction. According to Newton’s third law, this generates an equal and opposite reaction force, which causes acceleration. Strictly speaking, the Earth also receives an impulse in the opposite direction, but this can be neglected due to the massive difference in mass.
However, friction can also have unwanted effects. For example, a car slows down if energy is not continuously supplied by burning fuel.
In the human body, friction would cause significant wear between bones. To prevent this, joint capsules are lined with an inner membrane that secretes joint fluid (synovia), which greatly reduces friction—similar to oiling a hinge. Additionally, cartilage in the joints also contributes to reducing friction between the bones.