Washboard Roads Happen
Nicolas Taberlet, Stephen W. Morris, and Jim N. McElwaine
Physical Review Letters
A bane to motorists and road commissioners alike, the causes of washboard roads are surprisingly difficult to untangle. An international collaboration of French, Canadian, and British physicists have recently shed new light on the factors that cause these pesky ridges to form on unpaved roads.
Unfortunately, their study demonstrates that washboard road is inevitable. The ridges form regardless of the diameter of the wheel, wheel suspension, and the average size of the gravel. Even if we managed to drive with square wheels or paved our roads with long grain rice, washboard patterns would still occur. In agreement with previous research, the investigation confirmed that the ripples do not form below a critical speed. However, imposing this speed limit on rural roads would make for a rather impractical solution because it is just over 3 mph.
A computer simulation recreated gravel roads in two dimensions as a collection of variously sized disks. When a two-dimensional wheel rolled over the two dimensional gravel, peaks began to form. They resembled real washboard ridges as they rose gradually and dropped sharply in the direction of traffic. Even in the world of the Mario Brothers, the washboard roads are an inexorable result of driving on dirt roads. -KM
Layered Charge in the Neutron
Gerald A. Miller
Physical Review Letters
Unlike positively charged protons and negatively charged electrons, neutrons have no net electrical charge. Nevertheless, there contain regions of both negative and positive charge that precisely cancel out inside the particle.
Just how the charges are distributed in the neutron has long been a matter of speculation. A new analysis by physicist Gerald Miller of the University of Washington in Seattle shows that the neutron is built of alternating layers of charge - a negative inner core and a negative outer layer, with a positive charge layer sandwiched in between.
The structure is at odds with a common view, first put forth by physicist Enrico Fermi in 1947, that the neutron consists of a positive core surrounded a cloud of negative charge.
Miller attributes the detailed insight into neutron structure to high quality data recently provided by the Jefferson Laboratory in Virginia, the MIT Bates Laboratory in Massachusetts, and the MAMI particle accelerator lab in Mainz, Germany, as well as novel analyses of neutrons moving close to the speed of light. - JR
Katherine McAlpine and James Riordon contributed to this Tip Sheet.
