APS Physics Tip Sheet #60

Folk lore is filled with tales of quirky balls of lightning chasing cattle and drifting through windows to light the curtains on fire. Researchers and amateur scientists have made their own versions of ball lighting, usually with the aid of microwave sources that power balls of plasma. But it has not always been clear how much the fireballs resemble their natural counterparts. Now researchers at Tel Aviv University report that they have built a system that creates plasma fireballs in much the same way that they may be produced in lightning strikes. The laboratory fireballs don't last as long as ball lightning seems to, according to anecdotal reports anyway, and they tend to melt and break glass rather than drift through. They are also smaller and shorter lived than the natural form. However, the fireballs float in air, just as ball lightning is reported to float. They also can be formed in a variety of shapes, can split into smaller fireballs, and stick to or bounce along metal objects in the same way that ball lightning is said to behave. The researchers produced their fireballs inside a closed container by injecting microwave energy through a pointed rod into a substrate of glass, germanium, alumina, or various other materials. The energy leads to the formation of a molten hotspot that is pulled out of the substrate by lifting the pointed rod away from the surface, which creates a drop of hot material that expands into a floating, stable fireball. In addition to providing insight into the ball lightning legend, the researchers believe their work may lead to applications for material processing and thin film deposition as well as aiding in lightning research and plasma confinement techniques.

Space Drips
Ronald Suryo and Osman A. Basaran
Physical Review Letters
http://link.aps.org/abstract/PRL/v96/e034504

Living in space has its disadvantages, as visitors to the International Space Station sometimes testify, but at least astronauts don't have to listen to the incessant dripping of a leaky faucet in the Space Station lavatories. All that peace and quiet may now be at risk, thanks to new simulations that show how to make liquids drip from an opening, even in the absence of gravity's tug. Researchers at Purdue University have shown numerically that applying heat to the region where a droplet contacts the mouth of a tube would cause it to break free and be ejected as a drip, despite the fact that whole system is in simulated freefall. It is not likely that anyone is going to go to that much trouble to keep astronauts up at night looking for the plumber's number, but the development could lead to ways down on Earth to make very tiny drops for printing and microscale manufacturing.