Related Experiment Video
Updated: May 2, 2026

An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids
Published on: December 4, 2017
The undulation force; theoretical results versus experimental demonstrations
Håkan Wennerström1, Ulf Olsson1
1Division of Physical Chemistry, Department of Chemistry, Lund University, P.O. Box 124, SE-22100 Lund, Sweden.
Abstract:
In 1978 Wolfgang Helfrich published a paper (Helfrich W. Z Naturforsch 1978; 33a:305) where he introduced the notion of an undulation force between bilayers. This is caused by thermal excitations of the bending modes being restricted by the presence of neighboring layers. Although there is now a consensus on the qualitative picture put forward by Helfrich there is still a debate concerning the quantitative aspects. We discuss in particular the distance dependence of the interaction and also the value of the numerical coefficient of the force law derived by Helfrich.
Related Concept Videos
Forced Oscillations
Types of Damping
Two-Dimensional Force System
Damped Oscillations
Although friction and other non-conservative...
Hydrostatic Pressure Force on a Curved Surface
Three-Dimensional Force System

