We first consider the longitudinal angular momentum density j$_{z}$ which can be regarded as the combined contributions of spin and orbital parts: The longitudinal angular momentum will provide a simple way to understand why the circularly polarized wavepacket exhibits the optical Magnus effect. Figure 6 presents the distribution of longitudinal angular momentum density for the model [W]. Very surprisingly, this polarization model of wavepacket possesses polarization- dependent orbital angular momentum density [Figs. 6(a) and 6(d)]. However, the spin momentum density exhibits a significantly different distribution [Figs. 6(b) and 6(e)]. For the left circular polarization σ = +1, the total angular momentum density in the exterior part of wavepacket is positive j$_{z}$ > 0, while in the inner part is negative j$_{z}$ < 0 [Fig. 6(c)]. This means that the outer part of the packet presents an anticlockwise rotation, the inner part undergoes a clockwise one. For the right circular polarization σ = − 1, the total angular momentum density of wavepacket presents an oppositive distribution [Fig. 6(f)]. Thus, the rotating wavepacket cannot be regarded as a rigid ball as in the mechanical Magnus effect. This is the reason why we choose the centroid as the reference point to describe the polarization-dependent trajectories. For the comparison, we plot the longitudinal momentum density of the model [II] in Fig. 7. By comparing with the model [W], we find that the orbital angular momentum density vanishes in the present polarization model [Figs. 7(a) and 7(d)]. Thus, only the spin momentum density exhibits a polarization-dependent distribution [Figs. 7(b) and 7(e)]. For the left circular polarization σ = +1, the total angular momentum density first increases then decreases with the increase of r as shown in Fig. 7(c). For the right circular polarization σ = − 1, the total angular momentum density presents an oppositive distribution as shown in Fig. 7(f). The transverse intensity distribution is axially symmetric and the polarization- dependent rotation, if it exists, cannot be observed directly. Now we want to enquire what roles the angular momentum play in the optical Magnus effect. To answer this question needs to discuss the transverse angular momentum. The time- averaged linear momentum and angular momentum, which can be obtained by integrating 14 j [M] Oz = xp [M] Oy − yp [M] $_{Ox}$, (34) j [M] Sz = xp [M] Sy − yp [M] $_{Sx}$. (35)