Q: The surfaces of the bones at the joints are covered with a smooth layer of cartilage, which reduces what force between the bones when they move?


Read this paragraph and choose the correct option from the provided answers:

Movable joints allow the greatest movement and are the most common. In these joints, the bones are connected by ligaments. The surfaces of the bones at the joints are covered with a smooth layer of cartilage. It reduces friction between the bones when they move. The space between the bones is also filled with a liquid called synovial fluid. It helps to cushion the bones. There are several different types of movable joints. You can see three of them in Figure below . Move these three joints in your own skeleton to experience the range of motion each allows.

 Choices:

- vibration

- expulsion

- gravity

- friction


A:
friction