Question

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 F⃗ d on the head of the femur into the hip socket. Then, a horizontal force F⃗ h is applied and increased in magnitude until the femur head rotates clockwise in the socket. The joint is mounted in such a way that F⃗ h will cause clockwise rotation, not straight-line motion to the right. The friction force will point in a direction to oppose this rotation. Draw vectors indicating the normal force n⃗ (magnitude and direction) and the frictional force (direction only) acting on the femur head at point A. Assume that the weight of the femur is negligible compared to the applied downward force.

Answer 1

See the attached drawing

Step-by-step explanation:

Consider that the magnitude of the downward force
`F_(d)` will be equal although in opposite direction to the normal force n as shown in the diagram. During the rotation of the bone in clockwise direction, there will be frictional force which will counter the motion. Therefore, the frictional force will apply towards the right in order to oppose motion at point A as shown.