Credit: © 2009 APS

When two objects collide, one expects them to lose some or all of their speed owing to the dissipation of heat. Now it seems that this rule doesn't necessarily apply in the nanoworld. Researchers in Japan have shown that nanoscale clusters of atoms can collide and then bounce apart with more kinetic energy than they started with1.

Hiroto Kuninaka at Chuo University in Tokyo and Hisao Hayawaka at Kyoto University ran computer simulations of head-on collisions between two clusters, each containing several hundred atoms. They found that clusters with low attractive forces and relatively high temperatures could rebound at speeds up to 1.05 times their speed before the collision.

The researchers explain that the atoms in the clusters vibrate more vigorously at high temperatures, and if enough of them happen to be vibrating in the right direction they give an extra push during the collision. This may appear to violate the second law of thermodynamics, but actually highlights the fact that thermal motions have a large effect on nanosize objects.

This phenomenon could have strong implications in the development of nanoscale devices. It could even apply to dust particle collisions in space — the first steps in forming planets.