Category Archives: Physics

Get a Grip

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Balloon filled with ground coffee makes ideal robotic gripper

Particulate materials have a so-called jamming transition, which turns their behavior from fluid-like to solid-like when the particles can no longer slide past each other.

This phenomenon is familiar to coffee drinkers familiar with vacuum-packed coffee, which is hard as a brick until the package is unsealed.

Pretty neat (other than the part where they talk about a vacuum sucking the air out — it’s the external pressure that forces the air movement.)

Stretching that Hit

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Winning the World Series with math

To figure out just how critical the turns are, Carozza did a calculation comparing the straight-line path with a circle around the bases. A path that follows a circle turned out to be a whopping 25 percent faster.

When Carozza presented his calculation at a colloquium talk in the math department at Williams College, Stewart Johnson, one of the professors in the audience, got intrigued. The circular path is so long that it can hardly be the fastest, he figured. So what path is the fastest?

Johnson ran a simulation on his computer, tweaking the circular path in tiny ways to make it shorter and faster, until no more tweaks could improve it. The result was surprisingly close to a circle, both in its shape and its speed: It swung nearly as wide and was only 6 percent faster than Carozza’s circle.

…

“This cries out for an empirical test,” Winston says. “It would be easy to do. If it holds up, God, that goes in the New York Times sports section.”

This isn't the NFL

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(The NFL likes parity)

Largest Parity Violation and Other Adventures in Table-Top Physics: Atomic Experiments Push Boundary of Known Physical World

Budker uses atoms of the rare Earth element ytterbium to observe the largest extent of parity violation ever seen in atoms, larger by a factor of 100 compared to previous tests. His goal is to improve the precision of this measurement so that researchers could begin to use the parity-violating process to help measure the distribution of neutrons in nuclei.

Previous experiments from a dozen years ago used Cesium. The parity nonconservation was probed by looking at transitions between S orbital states (6S and 7S for Cesium). The electromagnetic transition between these states is highly forbidden (both having the same angular momentum and even parity) But because the orbitals are spherical they include the nucleus, and the weak interaction mixes in a tiny bit of a P-state transition (odd parity), which is allowed. It’s a tough experiment because you are looking for the small difference between the transitions when you reverse everything, and you start out with a small transition probability. I recall this because we tried trapping Francium when I was at TRIUMF, with the goal of providing an atom with a potentially larger parity-nonconserving subject. The effect varies with Z, and Francium was expected to give an effect that was ~18 times larger than Cesium. We weren’t successful (then) at trapping any, though we did succeed at piquing the interest of a nuclear watchdog organization.

Physics Can Save Your life

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Driver thanks man who hit him on purpose

“We realized he wasn’t slowing down, and if he hit someone at full speed, it would’ve been a very bad scene,” Innes said. The intersection with Southwest Grady Way was a few hundred yards away. “He could’ve very easily unknowingly taken out a whole row of traffic.”

Instinctively, Innes applied his 25 years of experience at Boeing, where he is a manager for the F22 fighter-jet program.

“The best-case scenario is I need to match his speed, get in front of him and let him hit me,” Innes remembers thinking.

…

Pace’s pickup hit the minivan, and Innes held onto the brakes to halt both vehicles. When they stopped, he knocked on the pickup’s window to alert Pace, who was by then semiconscious, and got him to unlock the door.

The Evil Twin Paradox

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Twin Paradox a Paradox in Low-Earth Orbit

In March 2011, if all goes as planned, two twin brothers will meet in space for the first time ever. On Feb. 27, astronaut Mark Kelly (the one with the mustache) will launch aboard NASA’s space shuttle Endeavour to meet up with his twin brother Scott who’s currently flying aboard the International Space Station (ISS). Scott made the trip up to the orbiting laboratory on a Russian Soyuz rocket launched on Oct. 7 and will be on board for the next sixth months.

I’m obliged to report this not only for the physics, but also for the name-dropping. Mark Kelly was the commander of STS-124, which is the group that visited the observatory — and toured my lab — a few years ago. Now I find out he has a twin, which not only raises the question of the twin paradox, but also this: which one is the evil twin?

The article raises the question of which effect dominates for the ISS — the kinematic or gravitational time dilation? They have opposite signs, with rising in the gravitational potential speeding the clock up, and motion slowing it down. For GPS satellites, the gravitational term is much larger than the kinematic term, but the ISS and shuttle live in low-earth orbit, and the kinematic term dominates there, as shown in this analysis, so a clock on the ISS will run slow by about 28 microseconds per day.

Outwitting or Nitwitting?

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German “heatball” wheeze outwits EU light bulb ban

Rotthaeuser studied EU legislation and realized that because the inefficient old bulbs produce more warmth than light — he calculated heat makes up 95 percent of their output, and light just 5 percent — they could be sold legally as heaters.

Technically 100% of the output is heat, because the visible light is heat, as it is part of the blackbody spectrum. So they’re right — it is a “heatball,” as are all light bulbs. However, the whole point is that 95% of the energy is wasted if your goal is to generate visible light. What’s interesting is that electricity is considerably more expensive in Germany than in the US, so compact fluorescents pay for themselves faster and make even more economic sense (and soon will LED systems, as well). So these people are throwing money away, in their passive-aggressive protesting way.