Physics in Your World Archive - Page 4

Image credit: Andrew Davidhazy, Rochester Institute of Technology

Wikipedia: Shadowgraph - Dec 1, 2010

This is a Schlieren image, which reveals differences in the density of air above the candles. To find out more about these images, visit Wikipedia: Shadowgraph, and to learn how to make one, visit Schlieren Photography Principles.

- Making one of these images is more complicated than making a shadowgraph, such as the image in From Physics Research.
- For more high-speed images by Andrew Davidhazy, visit this page.

image credit: Marco Nero (lasers by Wicked Lasers); image source; larger image

Physics 2000: Lasers - Nov 1, 2010

Lasers don't come only in red: you can buy handheld lasers that produce light in various wavelengths in the visible spectrum. Remember, lasers can be dangerous--so get adult supervision for any laser experiment you try.

- To learn how lasers work, check out the University of Colorado site Physics 2000: Lasers with several helpful applets.
- For some information on the differences between lasers that produce different colors, see this Laser Colors Q & A from the University of Illinois.
- And to learn about a laser that produces infrared light, see the feature at right on quantum cascade lasers.

image credit: Eurico Zimbres, Wikimedia Commons (taken at the San Diego Natural History Museum); image source; larger image

What Really Killed the Dinosaurs? - Oct 16, 2010

Dig into rocks around the globe at the right depth and you may find a thin layer like the one pictured above, a geological hint about our planet's past. This sedimentary layer contains much more iridium than the surrounding layers, and the element iridium is rarely found on Earth but plentiful in rocks in space. For this reason, some scientists believe that there was an enormous meteorite impact that covered the planet in its dust.

The iridium layer supports the impact catastrophe theory that dinosaurs of the late Cretaceous were killed by a meteorite impact and its ensuing planet-wide effects. However, new evidence suggests the crater thought to be responsible due to its iridium content (pictured at right) happened before the mass extinction. See What Really Killed the Dinosaurs? for more on the debate.

(This feature was updated on July 31, 2013.)

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.

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.

(This feature was updated on July 25, 2013.)

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.

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.)

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