Lopsided galaxies shed light on the speed of dark matter

In new research published in Astronomy & Astrophysics, researchers have figured out how to precisely calculate the forces that affect galaxies in tidal cycles. The next stage is to find galaxies sufficiently lopsided in the ...

Control over friction, from small to large scales

Friction is hard to predict and control, especially since surfaces that come in contact are rarely perfectly flat. New experiments demonstrate that the amount of friction between two silicon surfaces, even at large scales, ...

Researchers dynamically tune friction in graphene

The friction on a graphene surface can be dynamically tuned using external electric fields, according to researchers at the University of Illinois Urbana-Champaign led by Professor Rosa Espinosa-Marzal of the Department of ...

Inclined drops: New model allows description of slipping drops

The behavior of drops on surfaces is of interest for a variety of applications. However, properties such as velocity, friction or shape on inclined surfaces depend on a large number of parameters—their behavior is still ...

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Friction

Friction is the force resisting the relative lateral (tangential) motion of solid surfaces, fluid layers, or material elements in contact. It is usually subdivided into several varieties:

Friction is not a fundamental force, as it is derived from electromagnetic force between charged particles, including electrons, protons, atoms, and molecules, and so cannot be calculated from first principles, but instead must be found empirically. When contacting surfaces move relative to each other, the friction between the two surfaces converts kinetic energy into thermal energy, or heat. Contrary to earlier explanations, kinetic friction is now understood not to be caused by surface roughness but by chemical bonding between the surfaces. Surface roughness and contact area, however, do affect kinetic friction for micro- and nano-scale objects where surface area forces dominate inertial forces.

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