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Detailed insight into friction: How objects begin to slide

Detailed insight into friction: How objects start to slide
The researchers dragged a sphere over a glass surface decorated with special fluorescent molecules. Credit: HIMS / UvA

Chemists and physicists at the University of Amsterdam reveal a crucial facet of friction: how things commence to slide. Using fluorescence microscopy and dedicated fluorescent molecules, they could pinpoint how so when the friction at the contact between two objects is overcome and sliding starts that occurs. They report on the facts of the important transition from static to dynamic friction in The Journal of Physical Chemistry Letters.

Friction is in charge of around 25% of world energy consumption. Among the key questions for the stability of several systems is how so when objects begin to slide regarding each otherthink of earthquakes or your foot on the floor. When two objects touch, the contact area is formed by the countless microscopic protrusions of both interfaces that touch and interlock. Application of a shear force makes the objects slide along one another, breaking these initial contacts.

Dragging a sphere over a glass surface

At the University of Amsterdam, the sets of Prof. Daniel Bonn (Institute of Physics) and Prof. Fred Brouwer (Van ‘t Hoff Institute of Molecular Sciences) have a continuing cooperation to research the procedure of friction right down to the microscopic degree of roughness. In the paper just published in The Journal of Physical Chemistry Letters they report on experiments in which a sphere is dragged over a glass surface.

The has been decorated with a particular kind of molecules (fluorogenic mechanophores) that begin to emit light (fluorescence) when beneath the stress of the shearing force. As soon as this force disappears, the molecules go back to their stable, non-fluorescent form.

This enables scientists to directly visualize and quantify the microscopic shear force right down to the microscopic roughness level, and establish how it evolves through the transition from the static to the moving state. The researchers find, among other activities, that right before sliding occurs, a slip wave propagates from the edge toward the biggest market of the macroscopic . This enables for a quantitative and microscopic local knowledge of how surfaces begin to slide.

Credit: University of Amsterdam


More info: Chao-Chun Hsu et al, Local Shearing Force Measurement during Frictional Sliding Using Fluorogenic Mechanophores, The Journal of Physical Chemistry Letters (2022). DOI: 10.1021/acs.jpclett.2c02010

Citation: Detailed insight into friction: How objects begin to slide (2022, September 22) retrieved 22 September 2022 from https://phys.org/news/2022-09-insight-friction.html

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