![Fig. 2.15 — Trapping non-convex shapes and windmill effect](https://i0.wp.com/opticaltweezers.org/wp-content/uploads/2015/11/Fig2_15.png?fit=660%2C331)
(a) Multiple scattering of a ray on a complex shape constituted by two spheres one inside the other; this is a simple optical model for a cell containing a nucleus. (b) The asymmetric deflection of the incoming rays on a non-cylindrically-symmetric object produces the torque indicated by the black arrows and the rotation of the object. This phenomenon is known as the windmill effect.
Fig. 2.15 — Trapping non-convex shapes and windmill effect