image credit: U.S. Department of Energy; image source; larger image

Radioisotope Power Systems - Jul 1, 2012

The glowing pellet is an oxide of plutonium, the fuel for a radioisotope thermoelectric generator (RTG). It is photographed in the light it emits, because its radioactive decay produces considerable heat. The RTG converts this heat into electricity.

RTGs power the spacecraft that visited Mars, Jupiter, and Saturn--and the RTG keeps working over decades. To find out more, visit Radioisotope Power Systems.

image credit: NC State Department of Physics; image source; higher-res image/

The Invention of the Electric Guitar - Jun 1, 2012

The photo shows a modern electric guitar prototype developed in 1940 by a physicist at North Carolina State University. Check out this NCSU webpage to learn more.

Read about the development of the electric guitar in The Invention of the Electric Guitar.

image credit: U.S. Air Force; image source; larger image

Newton's 3rd Law - May 1, 2012

What is the purpose of the small rotor on the back of this helicopter? In fact, it's needed because of Newton's third law--for every action force there is an equal and opposite reaction. The helicopter puts a force on the main rotor shaft to make it turn, and the rotor shaft puts an equal and opposite force back on the helicopter.

This reaction force creates a torque that, by itself, would make the helicopter spin in the opposite direction as the rotor. To counter this torque, the small rotor on the tail creates an opposing torque, so the two are balanced.

To learn more, see Newton's 3rd Law. For an example of reaction forces, see this video.

image credit: CERN; image source; larger image

X-rays from free electrons - Apr 1, 2012

The spiral track above was made by an electron moving in a magnetic field. Since motion along a curved path requires a force perpendicular to the direction of motion, the electron is accelerated. Accelerated charges radiate electromagnetic waves, so the electron loses energy and spirals inward. To learn more about this process, see X-rays from free electrons.

image credit: A. Mugarza, C. Krull, S. Stepanow, G. Ceballos, and P. Gambardella, CIN2; image source; larger image

Electronic Handedness in Copper-Silver Combo - Mar 1, 2012

Notice how the two images above have opposite handedness? These images show electronic properties of a small layer of copper on top of silver, but neither silver nor copper have any handedness themselves. To learn more, visit this American Physical Society webpage.

image credit: D. Lafreniere, R. Jayawardhana, M. van Kerkwijk (University of Toronto); image source; larger image

APOD: Companion of a Young, Sun-like Star Confirmed - Feb 1, 2012

You are looking at the first telescopic image of a confirmed planet in orbit around a Sun-like star. The young planet is still quite warm, and therefore radiating considerable energy, which makes it relatively easy to detect. To learn more, see APOD: Companion of a Young, Sun-like Star Confirmed.

image credit: Odile Labbe, ONERA; image source; larger image

Wing Vortices - Jan 1, 2012

This image from ONERA, the French aerospace lab, shows a simulation of the wake of an aircraft, looking along the direction the aircraft is moving. To learn more, visit Wing Vortices, and be sure to check out the diagrams there.

Also, compare the image above with this photo (from PTG Issue 33, in the Archives) showing the pattern of smoke released behind the wingtip of a crop-duster. How well did the simulation model the crop-duster wake?

image credit: Prof. Markus Zahn; image source ; larger image

Fluid morphs into startling designs, surprising MIT researchers - Dec 1, 2011

This ferrofluid was subjected to a magnetic field perpendicular to its surface. The surface broke up into hexagonal regions, each with its own spike. For a MIT News article showing other ferrofluid patterns created by the same physicist, see Fluid morphs into startling designs, surprising MIT researchers.

image credit: André Karwath, Creative Commons; image source; second image courtesy of NPL

Time Flies - Nov 1, 2011

Einstein's theory of special relativity says that a moving clock, when compared to a stationary clock, runs slow. And general relativity, his theory of gravity, says that the weaker the gravitational field, the faster a clock in that field runs. These predictions were tested in 1971 by flying atomic clocks around the world. Einstein's relativity theories correctly explained what happened.

To learn about a more accurate update to this experiment 25 years later, see Time Flies. Click on the image to see a photo of the atomic clocks in the updated experiment.

image credit: National Oceanic and Atmospheric Administration/Department of Commerce; image source; larger image

The Contrail Effect - Oct 1, 2011

The false-color image above shows jet contrails in the skies above the mid-Atlantic coast on 1/26/2001. Check out this NASA photo of the sky taken on the ground at about the same time. Visit The Contrail Effect to find out how contrails can affect Earth's climate, and how this was investigated after 9/11.