Tag: reflection

Reflecting in a Stream
Total internal reflection traps three lasers in a stream of falling water. When light tries to pass from the water – a material with a high refractive index – to the air – which has a lower index of fraction – it can only do so if its angle of incidence is smaller than the critical angle. Here, the light impacts the water-air boundary at a large angle and rather than refracting across the interface – like the distorted view of a straw in a glass of water – the laser light is completely reflected. Instead of escaping, the laser light is trapped, becoming a ribbon of light that swirls inside the water stream until the light is diffused. (Image credits: L. Yarnell et al.; F. Batrack et al.)
October 27, 2016
Overflowing Foam
Hitting a glass bottle full of a non-carbonated drink can shatter the bottle due to cavitation, but doing the same with a carbonated beverage can make the bottle overflow with foam. The video above breaks down the physics of this bar prank. It all begins with nucleation and the tiny bubbles of carbon dioxide that form in the liquid. Striking the top of the bottle generates a compression wave that travels through the liquid, shrinking bubbles as it passes. When it hits the bottom of the bottle, it gets reflected as an expansion wave that expands the bubbles. This reflection happens several times between the free surface of the liquid and the bottom of the bottle. The rapid collapse-and-expansion of the bubbles makes them implode into a cloud of tinier bubbles that expands until the local supply of carbon dioxide is used up. At this point, the buoyancy of the bubbles carries them upward in plumes, creating more bubbles with the dissolved carbon dioxide nearby. And, all of a sudden, you’ve got foam everywhere. Like all of this week’s videos, this video is an entry in the 2013 Gallery of Fluid Motion. (Video credit: J. Rodriguez-Rodriguez et al.)
October 17, 2013
Glinting Off Waves
Sunglint on the ocean surface can sometimes reveal different patterns in wave conditions. In the satellite photo above, we see the Canary Islands with wavering silvery wakes stretching to the southwest. The predominant wind direction over the islands is from the northeast. The rocky islands act as a wind-break, redirecting the flow and shadowing the ocean in their wake from much of it. As a result, fewer waves are stirred up in the islands’ wakes, thereby changing the local surface reflection properties and making this image possible. (Photo credit: NASA Earth Observatory)
June 24, 2013
The Colors of Soap
The brilliant and beautiful colors of a bubble are directly related the the thickness of the soap film surrounding it. When light shines on the soap film, some rays are reflected from the upper surface of the film, while others are refracted through the film and reflect off its lower surface. These reflected rays have different phase shifts and their interference is what causes the colors we observe. The color patterns themselves reveal the interior flow of the soap film, in which gravity tries to thin the film and surface tension tries to distribute the film evenly. (Photo credit: R. Kelly, A. Fish, D. Schwichtenberg, N. Travers, G. Seese)
June 20, 2013