The movement of sugar molecules when dissolved in water is called diffusion.

Here's why:

* Diffusion is the net movement of molecules from a region of higher concentration to a region of lower concentration.

* When you add sugar to water, the sugar molecules are initially concentrated in the area where you added them.

* Over time, the sugar molecules will move randomly throughout the water until they are evenly distributed.

This movement is driven by the second law of thermodynamics, which states that systems tend to move towards a state of higher entropy (disorder). The random movement of sugar molecules from a concentrated area to a less concentrated area increases the entropy of the system.