The Ups and Down of Friction

CERN Courier May 2012 Sciencewatch C OMPILED BY J OHN S WAIN , N ORTHEA S TERN U NIVER S ITY The ups and down of friction The exact nature of friction is still somewhat Nanomeasurement instruments can detect mysterious, despite having long been studied movement to a billionth of a metre. (Image by many physicists and engineers. In the credit: K U Leuven.) 17th century, Guillaume Amontons and Charles-Augustin de Coulomb attributed recording the curves of the up-and-down friction to tiny surface irregularities that motion of the object as it rises and falls mesh and impede horizontal motion, over small irregularities. Remarkably, this necessitating frequent vertical motions. phenomenon – known as lift-up hysteresis – These ideas fell somewhat to the wayside does not appear to have been shown before. in more recent adhesion-based theories Its measurement shows the complexity of of friction but they have recently received techniques to measure hysteresis curves in friction and, say the researchers, confirms renewed support from Farid Al-Bender and the normal displacement (perpendicular the intuition of Amontons and Coulomb. colleagues at the Katholieke Universiteit to the surface) of a sliding object as it is Leuven. pushed along. They tested various materials ● Further reading These researchers used nanoscale (paper, plastic and brass) at different speeds, F Al-Bender et al. 2012 Tribol. Lett. 46 23. Earthshine and life better for the fruit flies, the wasps avoided on other worlds Ice-age plant resurrected laying eggs in the alcoholic larvae. Fruit flies also seem to treat psychological One way to look for life on other planets It may not be quite problems with alcohol. Galit Shohat-Ophir is to look at spectroscopic signals of the the same scenario and colleagues at the University of chemical composition of their atmospheres, as in Jurassic Park, California in San Francisco found that male searching for compounds such as methane but Svetlana Yashina fruit flies are more likely to choose food or molecular oxygen, which are likely to and colleagues at the laced with alcohol after being rejected by a be produced by living things. The catch so Russian Academy of mate (something that might strike a chord far has been that the light from exoplanets Sciences in Puschchino in humans). Alcohol seems to raise levels is faint compared with that emitted by the managed to resurrect of neuropeptide F, a brain chemical that stars they orbit. Now, Michael Sterzik of the a 30,000-year-old Ice also rises after mating. The work suggests European Southern Observatory in Santiago Silene Age flowering plant. treatments for human alcoholism and and colleagues have a clever proposal. Light stenophylla They recovered fruit depression by raising levels of neuropeptide that comes through an atmosphere becomes regenerated tissue of the plant (Silene Y, the human analogue of neuropeptide F. polarized, allowing it to be separated from from tissue of stenophylla) from a unpolarized background. fossil fruit. fossilized squirrel burrow ● Further reading The researchers tested this idea with (Image credit: 38 m underground N F Milan et al. 2012 Current Biology 22 488. the Focal Reducer/Low-Dispersion S Yashina et al.) near the Kolyma river in G Shohat-Ophir et al. 2012 Science 335 1351. Spectrograph at the Very Large Telescope in Siberia. Chile, looking at earthshine reflected from By using growth hormones, the team Storing hydrogen in acid the Moon. They were able to find signatures managed to start the cells dividing again and of oxygen, ozone and water and indications were able to grow viable plants that actually A big challenge in using hydrogen for of vegetation, as well as the fractional bloomed. This sets a new record, shattering energy is how to store it. Jonathan Hull contributions of clouds and ocean surface. the previous record for a 1200-year-old lotus, of Brookhaven National Laboratory and This technique could offer a new way of which was grown in modern times. colleagues have shown that hydrogen can be studying distant planets and searching for stored in an aqueous solution of formic acid, life even before there is a means to go there ● Further reading the acid that burns in ant stings. At normal for a more direct look. S Yashina et al. 2012 Proc. Nat. Acad. Sci. 109 4008. temperatures and pressures – a big plus for this technique – an iridium catalyst can ● Further reading make hydrogen react with carbon dioxide M F Sterzik et al. 2012 Nature 483 64. Milan of Emory University in Atlanta and to make formic acid under slightly alkaline colleagues raised fruit-fly larvae infected conditions. Acidifying the solution releases Alcohol helps fruit flies with parasites from a wasp that lays eggs in pure hydrogen gas at high pressures. them. As many as 80 per cent of the infected People who drink a little whisky in the hopes larvae favoured alcohol-laced food, which ● Further reading of helping a cold may be surprised to find can kill off the parasites, as opposed to just J F Hull 2012 Nature Chemistry, doi:10.1038/ that fruit flies do something similar. Neil 30 per cent of the noninfested ones. Even nchem.1295. 12 CCMay12-Science.indd 12 12/04/2012 15:16 .

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