Abstract: In a rotating body or machinery that is equipped with at least one such rotating body, the power loss resulting from the inertial force, which is an internal force caused by the rotation of the rotating body, contributes to mechanical inefficiency, as well as being the cause of unnecessary heat generation, unnecessary machine strength requirements, increased weight, and increased costs. Provided are low-loss machines and engines that essentially eliminate or greatly reduce the power loss due to the aforementioned inertial force. The rotating body of this invention, or machine which is equipped with at least one such rotating body, greatly reduces or essentially makes zero the power loss resulting from the inertial force generated by the rotating or rocking motion of the rotating body due to its poor mass distribution. This inertial force is an internal force of a new concept which excludes the centrifugal force.