|
In the field of optics, a caustic is a set of rays of light that have been reflected or refracted by a curved surface and focused into another surface. The classic example of caustics or a network of caustics is the bands of light you get at the bottom of a pool when the light shines from above. The top of the waves crisscrossing the pool act like a convex lens concentrating light on a focal point. This is incidentally why they are called “caustics”, from the Greek “to burn”, as when sunlight is focused by a lens into a small area. If this focal point coincides with the bottom surface of the pool, the caustic band will be sharp, whereas if it doesn’t, the caustic band will be diffuse. On the other hand, the areas between the top of the waves have a concave shape and they act to disperse the light. This is why caustics are separated by areas that seem to be darker. In the video below, I have slowed down the network of caustics in a pool down to 240 frames per second. You can follow the caustic bands and see how they appear, disappear, merge, and separate continuously as a result of the pattern of waves on the surface of the water in the pool.
0 Comments
I have previously posted about tensegrity structures. These are structures where the integrity of the whole is maintained by tension among its components. In the video below I show you how to build a simple but amazing tensegrity structure. The video includes an appearance by Science Cat! We tend to associate tail wagging with dogs. Almost everyone has seen happy dogs shaking their tails, and we have jokes and cartoons about it. We even have the phase “wag the dog” to describe when a small or less powerful entity takes control of a bigger or more powerful one. Apart from signaling that they are happy, dogs use their tails to communicate various messages about themselves, but, as it turns out, there are other species of animals besides dogs that use their tails to communicate things, and one of them is cats. Dogs evolved from wolves (Canis Lupus), which live in packs, so they tend to be social and expressive animals. However, domestic cats are evolved from the African Wildcat (Felix sylvestris lybica), which are solitary nocturnal animals, so the tail signals of cats are different from those of dogs. When cats curve and swish their whole tail from side to side it may indicate excitement or deep focus as when stalking a prey. This is a common predatory behavior especially if the ears are standing upright. However, a tail moving back and forth can also signal irritation or pain especially when associated with arched backs and lowered heads. When the cat only swishes the tip of its tail, it indicates that they are about to pounce or they are playing, but it can also signal that they are annoyed. If a cat wants to signal it is happy, it will stick its tail straight up, which in dogs is a sign of alertness, not happiness. In the video below Science Cat demonstrates how cats wag their tails. She is intensely looking at some birds in the bush outside while swishing her tail with her ears upright. One very common illusion employed in theaters, museums, shows and other venues is Pepper’s Ghost. The illusion is named after English scientist John H. Pepper who improved upon a previous ingenious but cumbersome illusion developed by inventor Henry Dircks in 1860. Pepper made the first demonstration of this illusion in 1862. The illusion relies on the fact that whereas light goes through most transparent glasses, a certain percentage of it is reflected by the surface of the glass. In the classical Peppers Ghost illusion, a glass is installed at an angle facing an audience. The audience can see with no problem the action taking place in the stage behind the glass. At some point an actor or an object is illuminated in a compartment that is located to the side of the glass in such a way that the light coming from the actor or object will bounce off the glass and appear to the audience to be coming from the stage as a ghostly apparition. In the photo below, I use a window to generate a version of the Pepper’s Ghost illusion, where I seem to be within the tree outside as a ghostly apparition.  In the video I used an exhibit at the 2019 Prague Quadrennial. I manipulated the see-through and reflection qualities of the glass window of the exhibit as well as the proximity of my phone to the glass, to create a Peper’s Ghost illusion. Note: the photo belongs to the author and can only be used with permission. I woke up one day to gnawing sounds in the attic right above my bed. For the next few days these sounds continued and became very bothersome making it difficult to sleep. Science Cat heard them too. She would stand on her hind legs with her front legs against the wall and look at the ceiling. I suspected we had a squirrel up there. Squirrels are mammals which belong to the order Rodentia. These also include rats, mice, chipmunks, beavers, and porcupines. One defining characteristic of rodents is that they have pairs of sharp incisor teeth in their upper and lower jaws which grow continuously throughout their lives. As a result of this, rodents need to gnaw very often, even if they are not eating, to wear down their teeth. If they don’t do this, their teeth can grow so large that it can kill them by making eating problematic and even piercing the palate of their jaws. Because of this I knew that, if left unchecked, the squirrel could inflict significant damage to our attic overtime. I borrowed a humane animal trap from my neighbor, and following his advice I baited it with a Reese's Peanut Butter Cup (apparently squirrels are suckers for Reese's Peanut Butter Cups). I left the trap overnight in our attic. The next morning Science Cat seemed to hear something. She would pace back and forth in the room with access to the attic. When I placed the ladder to access the attic, she darted up the ladder and stood at the top looking up, so I had to bring her back down.  I opened the trapdoor to the attic, inspected the trap, and found the varmint. It turned out to be a specimen of Sciurus carolinensis or the eastern grey squirrel. Science Cat took great interest in the squirrel.  My wife and I drove the critter to a nearby forested location and released it into the wild as shown in the video below. There have been no more noises coming from the attic, and I am able to sleep once again just fine. The photos are property of the author and can only be used with permission.  Forced perspective is a technique that exploits the relationship between distance and size to make large objects appear smaller or vice versa. This technique has been exploited in movies such as The Lord of The Rings franchise to make actors appear smaller (Hobbits) with relation to other actors. The technique is also used by professional photographers to create illusions and also by amateur photographers to create fun pictures. The classic use of the force perspective technique is when people get photographed holding up the leaning tower of Pisa in Italy. I made a forced perspective photograph of my own while visiting the Rumsey Monument in Shepherdstown, West Virginia. This is a monument to a local inventor, James Rumsey, who in 1787 became the first person in the United States to build and pilot a steamboat. The monument, which is located near the Potomac River where Rumsey made his trek, contains a 75-foot-tall granite column capped with a globe. The column sits atop a 40 square feet concrete base. In the photograph I use forced perspective to make it look like I am wearing the column of the monument on my head!  Leaning tower of Pisa image from flickr by Jeffrey is used here under an Attribution-NoDerivs 2.0 Generic (CC BY-ND 2.0) license. The photographs of the Rumsey monuments belong to the author and can only be used with permission. The video below features a stela found in the Mayan city of Caracol in Belize, which is exhibited at the Penn Museum in Pennsylvania. Mayans used these stones to mark time. This stela, which shows an image of the ruling king, celebrates a date equivalent to May 10, 613 CE. The stone features an elaborate design that includes the ruler, his attire, and portraits of his ancestors. Besides the anthropological and historical significance of the stone, a thing that caught my attention is how the lines in the figure on the stone were traced. The creators of the museum exhibit chose an LCD light projector that traces with white lines the contours of the design of the stone when you press a button and them untraces them after several seconds as is shown in the video. I thought it would be interesting to film the tracing of the design by the projector in slow motion, but I was surprised by the video I obtained which showed the white lines of the stone flickering in a pattern that moved from left to right and that seemed to display occasional flashes of color. When I examined the video frame by frame, I found that the LCD projector did not use white light to create the lines at all. It used an alternating pattern of blue, purple (or red), yellow, and green lines to create the sensation of white lines. This pattern had an apparent left to right movement which maybe has to do with the very fast transition from one color to another.. These types of projectors are quite sophisticated, and if you are interested you can find an explanation of how they work here. The photographs of the stela can only be used with permission of the author. While visiting the Lee County Conservation Center in Heron Bend, Lee County, Iowa, I came upon a really cool and fun tool to learn topography. The US Geological Survey calls this tool an “augmented reality sandbox”, and the model at the Lee County Conservation Center was obtained from Idea Fab Labs. Their tool uses a 3D camera, a digital projector, and software that gauges depth and superimposes contour lines on shapes in sandboxes. The tool also allows you to create “rain” by waving your hand on top of the sand so you can see the way watersheds work. I wish I had had access to one of these when I was a kid! The video below shows a wood stove fan. These fans function with no outside input of electricity. They use the heat gradient between the bottom of the fan in contact with the stove and the top of the fan, which is designed to radiate heat. The bottom to top flow of heat goes through an array of semiconductors. Semiconductors are used in most electronic devices today ranging from smartphones to computers. Semiconductors contain elements such as germanium or compounds such as cadmium selenide combined with specific impurities that alter their physical properties. In the case of the fan, the elements of the semiconductor sandwiched between the hot and cooler areas of the gradient produce an electric current (Seebeck Effect) that is used to drive a small motor which rotates the blades of the fan. The rotating of the blades propels heat from the stove into the room and helps further cool the top of the fan enhancing the bottom to top heat gradient. On a recent trip to the University of Tennessee (UT) we learned that robots were delivering food on campus, so we placed an order for Chinese food from the restaurant Panda Express. The robot arrived with our food about 25 minutes after we ordered. When we opened the lid of the robot, it played the song I had chosen (Here Comes the Sun by The Beatles). After retrieving the food and closing the lid, the robot said, “Thank you, go Vols” (the UT team is the “Volunteers”) and drove away. These self-driving food delivery robots are the creation of the company Starship Technologies. The robots use a combination of machine learning, artificial intelligence, and sensors to cross streets and avoid pedestrians and other obstacles. They can deliver the food during rain, snow, or heat. The company has placed its robots in several university campuses in the U.S. and throughout the world. Is this the future of food delivery? And what is next? Mail, packages, drones? The future is creeping closer and closer to the present! |
Categories
All
Archives
September 2022
|
RSS Feed
