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Lamar University
Dan F. Smith Department of Chemical Engineering
News Release
Monday, November 23, 2009

Dr. Rafael Tadmor with the device used to demonstrate a new physics of friction.Beaumont, TX — Lamar University associate professor Rafael Tadmor and a team of students recently found a way to bring what had only been a physics theory to the realm of experimental fact. Their effort, and the device they built to test the theories will be discussed in a number of leading scientific journals.

For decades, students have learned in introductory physics classes that the friction force — which must be overcome to, say, slide a block down an inclined plane — is the product of a friction coefficient and the force normal to the surface. That relationship has been superseded over the past 50 years by the recognition that the lateral friction is, in fact, proportional to the true contact area. 

The approach taught in introductory physics courses is a special but common case in which the contact area scales linearly with the normal force.

Using a special device that allows complete decoupling of normal and lateral retention forces, a group of student researchers led by Rafael Tadmor, associate professor in the Dan F. Smith Department of Chemical Engineering at Lamar University, found a system in which the lateral force decreases – rather than increases – with the normal force in spite of the fact that the contact area increases. This discovery will be published in one of the most prestigious journals in science.

The article, “Measurement of lateral adhesion forces at the interface between a liquid drop and a substrate,” was accepted for publication and will appear in a future issue of Physical Review Letters, published by the American Physical Society. The findings will also be presented on the society’s public website ( and two publications, Physics Today and Physical Review Focus, written for a more general audience.

Tadmor holds a bachelor’s and master’s degree from Technical Israel Institute of Technology and the Ph.D. from Weizmann Institute of Science, Israel, and has been on faculty at Lamar since 2003. He was joined in the research by Ph.D. candidates Prashant Bahadur and Aisha Leh, master’s students Lan Dang and Hartmann N’guessan, and Rajiv Jaini, an undergraduate chemical engineering major.

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