# How many components does the net force have on a rotating object?

I understand that there is the radial and tangential force components acting on a spinning object, but according to the attached image from my book, there is a third component F_1z that is perpendicular to the other vector components and is along the axis of rotation.

I would understand if this was the vector for torque or angular acceleration, but it still seems to be talking about the components of linear force on the object. Does this force also signify the direction of the object? I've never heard of a third vector component when it comes to describing the linear forces of a rotating object.

• If the center of mass is accelerating along the axis of rotation, it would be a result of an axial force. Commented Dec 25, 2023 at 13:14

I believe you are thinking of motion in two dimensions, and so implicitly assuming that the axial force $$F_{1z}$$ is zero. However, if $$F_{1z}$$ is not zero then the rigid body will move up (or down) parallel to the $$z$$ axis while still rotating about the $$z$$ axis. In this case, the path of the particle $$m_1$$ will be a helix rather than a circle.