Friction describes how a body that is immersed in a fluid resists to dragging it. The friction experienced by the molecules of a liquid is a crucial parameter: it controls energy dissipation and sets the time scale of virtually all processes in liquid matter. On the other hand, the forces between individual molecules and atoms lead to motion that is free of dissipation. The origin of friction from such conservative forces remains as one of the grand challenges of the physics of fluids. The bridge between these atomistic and hydrodynamic pictures of the same liquid was found by researchers of the Freie Universität Berlin and Zuse Institute Berlin. They developed an approach that reveals an abrupt onset of friction reported in the journal “Communications Physics” (Nature Publishing).

A. V. Straube, B. G. Kowalik, R. R. Netz, and F. Höfling, 
Rapid onset of molecular friction in liquids bridging between the atomistic and hydrodynamic pictures, Commun. Phys. 3, 126 (2020). DOI: 10.1038/s42005-020-0389-0 

The picture shows smooth yet chaotic motion of atoms in a liquid.