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Starting a fire and controlling it was one of the key discoveries made by humankind. It affected many aspects of human history such as diet, agriculture, technology, and rituals. Fire and its flames have been a source of inspiration and metaphors for generations of artists and thinkers, as well as an object of research by scientists. But what is a flame? In a wood fire, there is a reaction between the wood and the oxygen in the air leading to the conversion of wood carbon to carbon dioxide (CO2) with the emission of heat and light. As the fire heats the air, it makes it less dense. So the heated air rises, and air from the periphery of the fire rushes in to take its place, feeding more oxygen to the fire and creating a current that blows elements of the fire upwards (a process called buoyant convection). Part of these elements are the small shapeshifting clouds of gases made up of hot carbon dioxide, water, oxygen, nitrogen, hydrogen, and other molecules that we call flames. Wood fire flames have a lot of very hot partially burnt or unburnt carbon compounds (soot particles). Some of these compounds are still in the process of burning up and give off light. However, most of the light in the flames comes from the very hot soot particles briefly producing a light of their own (called black body radiation) causing flames to have their characteristic yellow and orange color. Charcoal or propane fires, on the contrary, tend to emit blue flames because all the carbon present is burnt completely, and there is not soot. As the flames rise and dissipate, the soot cools down and ceases to give of light. In the video below you can see the flames of a wood fire filmed in slow motion.
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Look at the photograph below that I took of a surface at Locals, my favorite restaurant in Poolesville, Maryland.  If you were to slide your hand over this surface, would you find it smooth or bumpy? In the photograph below, the white arrow shows the part of the surface that I photographed above.  Yes, those diagonal grooves in the first photograph are nothing more than a pattern of light and dark bands on the floor produced by sunlight shinning through the blinds on a window!  The illusion shown in the first photograph has to do with the way our brain perceives contrast. We associate dark areas with surfaces that are blocked from receiving light (they are in a shadow) and lighter areas with surfaces that are exposed to light. When we see a pattern of alternating light and dark bands, our brains create the perception of relief (a grooved pattern) in the surface that we are looking at, even though it is very smooth. As I have mentioned before, we do not passively perceive the world as it is. Rather, our brain creates a representation of the world based on the information it receives, which is what we perceive. This representation is not veridical, it is fake, but it is correlated to reality, thus it is not false. However, there are many situations, such as the one I described here, where our perception of reality proves to be highly inaccurate. The way we perceive contrast is an active area of research in several scientific disciplines. The photographs belong to the author and can only be used with permission. We are so accustomed to seeing light around us that very few people realize that in a very clear environment you will not see a beam of light unless it is aimed at your eyes. The reason we see rays of light, even if they are not aimed at our eyes, is that there are particles in the environment that disperse the light. It is this dispersed light which we see when we see a beam of light not directed at us. Dispersion of light by particles in the environment is a very well-known effect used in entertainment. Theaters and other venues use fog machines that heat a solution of water and glycol producing vapor. The vapor is then expelled through a nozzle where it mixes with the cooler air in the theater to produce a particulate fog, which lingers in the air due to its density and can be fanned around the premises. This vapor will dissipate the light from any ray of light making it visible and creating great special effects. The video below shows a light shining through stage fog at the Signature Theater in Virginia. In the video below you can see a caterpillar of the sycamore tussock moth (Halysidota harrisii) moving and producing a wave that seems to run up its body in the direction of the movement. The way this happens is that the caterpillar contracts the muscles of the hind segment of its body which moves forward a bit. Once the legs in this segment (called prolegs) are anchored on the ground, the caterpillar relaxes the muscles in this segment while contracting those of the next, which is raised, moved forward, and its prolegs anchored to the ground, repeating the process for the next segment and so on. This sequential contraction and relaxation is what generates the tail to head waves as the caterpillar moves. Interestingly, scientists have discovered that this process is more complicated than it seems. It turns out that the first thing that is propelled forward is the tube of the gut followed by the rest of the body. This mode of locomotion has been named visceral locomotory pistoning. Air dancers (also known as tube men, inflatable men, sky dancers, tall boys, or fly guys) are a common sight at fairs, carnivals, car dealerships, and other venues. Air dancers are the brain child of Trinidad and Tobago artist Peter Minshall and Israeli artist Doron Gazit. These contraptions made their first appearance in the United States during the opening ceremony of the 1996 Olympics in Atlanta, and thereafter spread all over the world. The science behind what makes the air dancer “dance”, Bernoulli’s Principle, is the same science behind what allows airplanes to take off and stay in the air. Named after the Swiss mathematician and physicist Daniel Bernoulli, this principle states that an increase in the speed of a fluid (and air is considered a fluid) leads to a decrease in the pressure it exerts, with the opposite occurring when the speed of the fluid decreases. In the case of an airplane, the wind flowing over the wing flows faster (due to the shape of the wing) and generates less pressure than the wind flowing under the wing. This creates the lift force. In the case of the air dancer, when it collapses, the wind inside it flows slower creating a pressure that straightens up the tube. Once this happens, air can flow freely out of the end of the tube, increasing wind speed and decreasing pressure, which makes the tube collapse repeating the cycle. In the video below I stand next to a large air dancer at the Montgomery County Agricultural Fair in Maryland. Machines at several Science Centers throughout the nation display a model of a tornado that people can interact with. The machines use fans to create a rotating air current between the base and the ceiling and cold-water vapor to make the tornado visible. In the video you can see one such machine at work in the Maryland Science Center in Baltimore. There are many aspects of tornado formation that remain unknown. In general, tornados occur within a specific type of rotating thunderstorm called a “supercell”. Thunderstorms contain air currents flowing in different directions at different altitudes partly as a result of cold air sinking and hot air rising, a phenomenon called “windshear”. When wind at ground level flowing in one direction is overlaid by wind flowing in a different direction at a higher elevation, this can lead to the creation of a spinning tunnel of air that is parallel to the ground. The updrafts in a thunderstorm created by warm air rising can tilt these rotating tunnels and realign them in a vertical direction with respect to the ground, causing the whole thunderstorm to rotate creating a supercell. When the lower end of one of these rotating tunnels of wind within a supercell extends towards the ground, it is called a tornado, and can reach speeds in excess of 300 miles per hour. Fireworks are a beautiful sight, but few people are aware of the science behind them. The average firework is made up of a mortar with a charge placed at the bottom made up of gunpowder. On top of the charge sits a structure called the “shell” which contains all the material that produces the actual firework display known as the “stars”. When a fuse is lit, the charge ignites creating an explosion that propels the shell upwards. The shell in turn has a timed fuse that ignites at a certain height. This fuse detonates a secondary charge attached to the shell called the “burst charge”. When the burst charge explodes, it disperses the ignited stars in the shell creating the colored lights we admire during celebrations. To generate bursts of different colors, different elements are used in the fireworks. The principle is that when an element is heated, its atoms absorb this energy and then release it as light of a wavelength characteristic of the element. To create a red color, the firework’s stars are made from the element strontium. For orange, calcium is used. For yellow, green, and blue, sodium, barium, and copper are used, respectively. To obtain a purple color, strontium and copper are mixed in the shell, and to generate the color silver, magnesium and aluminum are used. To produce white light in the firework, magnesium and aluminum are combined with titanium. This, of course, is just a general explanation of the science behind fireworks. There are a lot of nuances to fireworks such as the sounds they make (booms, crackling, or whistling), and the force and timing of the explosions and their directionality with regards to the components of the shell in order to create random or specific patterns in space, also including effects such as strobe or sparks. The video below shows a firework display in Germantown, Maryland in 2013. Everybody is familiar with chainsaws nowadays. We associate them with cutting trees, carving wood, or with grislier applications such as those depicted in some horror films. However, the true reason why chainsaws were developed is far removed from the world of lumberjacks, woodcarvers, or slasher movie psychopaths. Chainsaws were developed to aid in childbirth and to facilitate surgeries that involved cutting bones! In the era before anesthesia, antibiotics, or knowledge about the role of germs in infection, when babies got stuck in the birth canal, C-sections were often fatal, so doctors figured out other ways to deliver the baby. For this they performed what is called a symphysiotomy. Towards the front of the body, the birth canal is surrounded by two bones (pubic bones) that are joined together by a joint made out of cartilage called the pubic symphysis. This joint is located above the external genitalia and in front of the bladder. In a symphysiotomy, a doctor would cut through this joint, thus widening the birth canal and allowing birth. In an era when surgery had to be performed very quickly to reduce risks of infection, symphysiotomy, although an improvement over C-sections, was still a risky and laborious procedure that was carried out with saws and knives. But in 1785, the Scottish doctors John Aitken and James Jeffray developed a cutting technique using a hand-powered fine serrated link chain that shortened the length of the procedure and improved its precision. Further refinements to the invention were made until the development of anesthesia and aseptic techniques by the start of the 20th century improved the safety of C-sections and rendered symphysiotomies obsolete. The first chainsaw bearing a resemblance to current chainsaws was made in 1830 by the German Physician Bernhard Heine. It consisted of a serrated link chain that was powered by a hand crank and was called the “osteotome”. The osteotome was used in surgeries that required cutting bone and was an improvement over earlier methods using hammers, chisels, and saws which left splinters and caused a lot of damage to soft tissue.  Osteotome Chain saws designed to cut wood were created at the beginning of the 20th century, and were modelled based on Heine’s osteotome, although they were bulky contraptions that had to be operated by more than one person. It would only be in the 1950’s that the first chainsaws operated by one person were made. Soon thereafter chainsaws began to be used for woodcarving as an art form. This art has evolved into a sophisticated activity featuring various styles, skill levels, and themes that are displayed in national and international competitions. The time-lapse video below was shot at the Montgomery County Agricultural fair in Gaithersburg, Maryland, and features the wood carving art of Joe Stebbing. The image of an osteotome is a private photo taken at Orthopädische Universitätsklinik Frankfurt by Sabine Salfer who has released it into the public domain. One Day I was going to wash the dishes that had accumulated in the sink, but when I turned on the water, something happened that is captured in the video below. Through sheer happenstance, the oven pan placed in the sink was balanced over other dishes in such a manner that when I turned on the water, it started cycling through filled and drained configurations. We had unwittingly created a relaxation oscillator! What is that? The term comes from electronics and refers to a circuit where flowing current charges a device such as a capacitor. Once the capacitor reaches a certain level of charge, it discharges and returns back to its initial uncharged state, only to be charged again by the current repeating the cycle. These oscillating circuits produce low frequency signals that are used in applications such as beepers and blinking lights. However, the term relaxation oscillator can be applied to any system which builds up energy and then releases it, just to build it up again with certain periodicity. One example of a relaxation oscillator is the Old Faithful geyser in Yellowstone National Park. And, as many of my readers have probably figured out by now, the particular relaxation oscillator in my sink has a more colloquial albeit less interesting name: tipping bucket. These contraptions are often found in water parks, works of art, and in applications such as rain gauges. I went to the National Gallery of Art in Washington D.C. and saw an artwork by Jack Whitten entitled Ascension I. This interesting piece was made by applying a tool to generate wavy lines in a background of acrylic paint to create the diagonal interlace pattern that you see in some baskets. Apart from the art itself, one of the things that caught my attention is that when I moved, the pattern of the art piece seemed to pulsate, displaying changes in color and giving off a glare. I was able to capture this with my phone camera in the video below. These optical effects are an example of what is called spatial aliasing. The most well-known example of spatial aliasing is when two grates or meshes are placed on top of each other and one of them is moved. A series of banding patterns appear, which are called interference patterns or Moiré patterns. Spatial aliasing occurs when a signal is not sampled often enough along an axis in space. Our eye and the camera do not monitor reality in a continuous fashion, instead they take samples and then put them together much in the same way that the sensation of movement is generated in a film by playing individual frames one after the other. Spatial aliasing is a problem in any branch of technology that involves waves, such as when playing or recording sounds or generating or producing light. Many industries, ranging from computer graphics to recording studios, implement anti-aliasing techniques to improve the quality of the images or the sound. Another modality of aliasing, called temporal aliasing, is produced when the sampling rate for the signal is insufficient over time. A classic example is the apparent change in rotation speed and direction of the spokes of a wheel. I have previously made a video of the phenomenon of temporal aliasing I observed when shooting a video of the railroad tracks from a moving train. The photos belong to the author and can only be used with permission. |
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