The transfer of molecules that bump into each other is called diffusion.

Here's why:

* Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration. This movement is driven by the random motion of molecules, which collide with each other and spread out.

* Bumping into each other is a description of the collisions that drive diffusion. These collisions cause the molecules to change direction and spread out over time.

Let me know if you have any other questions!