Abstract
It is well known that three dimensional motion of a rigid body can be described by a rotation about a fixed axis. Also, force and moment applied to a rigid body can be regard as a force along a line of action. The motions of the pelvis and the thorax, steering forces and torques of a driver on two different seats are visualized by instantaneous screw axis and line of action respectively. The screw axis of the thorax passes close to the center of mass of the head. Relative screw axis between thorax and pelvis goes through the center of mass of the upper body in both cases. The line of action regarding the steering force reaches the driver’s shoulder girdle when driving on the seat that has larger back support. The proposed method can be helpful to consideration of the driver’s motion from a mechanical view.
