Partial squeeze film levitation modulates fingertip friction

Michaël Wiertlewski*, Rebecca Fenton Friesen, J. Edward Colgate

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

46 Scopus citations


When touched, a glass plate excited with ultrasonic transverse waves feels notably more slippery than it does at rest. To study this phenomenon, we use frustrated total internal reflection to image the asperities of the skin that are in intimate contact with a glass plate. We observed that the load at the interface is shared between the elastic compression of the asperities of the skin and a squeeze film of air. Stroboscopic investigation reveals that the time evolution of the interfacial gap is partially out of phase with the plate vibration. Taken together, these results suggest that the skin bounces against the vibrating plate but that the bounces are cushioned by a squeeze film of air that does not have time to escape the interfacial separation. This behavior results in dynamic levitation, in which the average number of asperities in intimate contact is reduced, thereby reducing friction. This improved understanding of the physics of friction reduction provides key guidelines for designing interfaces that can dynamically modulate friction with soft materials and biological tissues, such as human fingertips.

Original languageEnglish (US)
Pages (from-to)9210-9215
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number33
StatePublished - Aug 16 2016


  • Acoustic
  • Biotribology
  • Haptics
  • Partial squeeze film levitation modulates fingertip friction
  • Roughness
  • Squeeze film

ASJC Scopus subject areas

  • General

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