image credit: William W Nazaroff (2005); image source; larger image

The Geothermal Power Plant - Oct 1, 2010

The above photo shows the Nesjavellir geothermal plant in Iceland, which produces power and hot water for the towns surrounding it. To learn more about how the plant works, see this site from the University of Rochester.

Iceland sits astride the mid-Atlantic ridge, where two tectonic plates are moving apart at about two and a half centimeters per year. Magma--molten rock--wells up in between the plates and heats the bedrock under Iceland. The bedrock heats the groundwater that the plant pipes to the surface to make a mixture of steam and brine (salt water).

For more on tectonic plates and Iceland, including a volcanic island nearby that was formed in 1963, see Physics to Go, Issue 55.

image credit: LVD Company n.v.; image source; larger image

Laser Applications - Sep 16, 2010

This laser cutting machine can cut metal up to 16 mm thick. Laser cutting is just one of many laser applications--lasers can cool atoms, bring stars into focus, and transmit information. To learn about many more applications, see this Hyperphysics webpage.

image credit: Eleni Katifori; image source; additional image

Why Leaves Aren't Trees - Sep 1, 2010

This is a lemon leaf that was wounded to interfere with its circulation. Note how the network of veins enabled nutrients to flow beyond the wound.

- Click on the image to see a similar experiment with a ginkgo leaf.
- To learn about the controversy over how these different vein structures developed, see Why Leaves Aren't Trees.

Image credit: Andrew Davidhazy; image source; Larger image

High speed photography - Aug 16, 2010

Look at the cavity behind the falling object that made this splash--you can learn how this cavity collapses if you check out From Physics Research.

- For more splash photos, see this page by Andrew Davidhazy, especially the splash sequence at the bottom.
- To learn about taking pictures that stop motion, see High speed photography.

Image credit: Malene Thyssen (Creative Commons); Image source; larger image

Ocean Waves - Aug 1, 2010

The side-view photo above shows how the back of a breaking wave spills over the front.

- This happens because as the wave enters more shallow water, its speed slows down, and the back of the wave overruns the front.
- If the reduction in depth happens quickly, the breaking wave creates a cylindrical cavity, as in the wave above.
- For more on ocean waves, see Ocean Waves and Ocean in Motion.

Image Credit: Denver International Airport; Image source; larger image

Tensile Structure - Jul 16, 2010

The roof of the Denver International Airport terminal (above) is a tensioned fabric structure designed by Horst Berger, a civil engineer famous for his large-scale fabric projects. This roof employs double-curved "minimal surfaces" that are characteristic of soap films (see From Physics Research).

- Visit Tensile Structure to learn more about this kind of construction.
- See this article from Structure magazine for information about Berger's career and numerous photos of his work.

(This feature was updated on March 25, 2012.)

image credit: Jim Gordon (Creative Commons); image source; larger image.

The Mystery of the Racing Rocks - Jul 1, 2010

What could cause rocks like this--of various sizes--to slide across the desert of Death Valley and leave these long tracks? The force of the wind... the force of moving ice sheets? To find out about these possibilities, visit The Mystery of the Racing Rocks.

Also check out The Sliding Tracks of Racetrack Playa for other explanations and more images.

(This feature was updated on 1/24/2013.)

image credit: U.S. Navy photo/Petty Officer 1st Class Ronald Dejarnett; Image source; Larger image

Scientific American: What happens when an aircraft breaks the sound barrier? - Jun 16, 2010

This is an Air Force F-22 Raptor producing a cloud as it breaks the sound barrier above an aircraft carrier.
- To learn more about how the cloud forms, and see a similar photo, check out Scientific American: What happens when an aircraft breaks the sound barrier?
- For more U.S. Navy pictures of these clouds see the Navy's Featured Galleries and search on "sound barrier."

To learn more, see Hyperphysics' Sound barrier.

image credit: ESO/S. Steinhöfel; image source; larger image

Star Life Cycle - Jun 1, 2010

Our Sun is typical low-mass star in the galaxy, in the prime of its life, steadily fusing hydrogen as it will do for another five billion years. For an overview of our Sun's and other stars' lives, check out Star Life Cycle. For more details, see Main Sequence Stars and Sol.

You have probably heard that the Sun will one day expand and consume the Earth.  In fact, the Sun might even expand to the orbit of Mars. Read what happens when stars leave the main sequence here.

image credit: University of Michigan Physics Department Lecture Demonstration Lab; image source; larger image

Physics in Action: Plasma Power - May 16, 2010

You've probably seen a plasma globe in class or at a novelty shop before.  The glass is filled with a low-pressure, inert gas, which becomes ionized by the electric current from the central electrode to form tendrils of plasma.

Understanding plasma may be the answer to our energy crisis. The tendrils of a plasma globe are the cool cousins of the fires within a star, which fusion researchers hope to reproduce on Earth. Read Physics in Action: Plasma Power to learn more about plasmas and fusion reactors.