Schlieren Optics Harvard Natural Sciences Lecture Demonstrations 2014-01-24 | Demonstration of an optical technique that allows us to see small changes in the index of refraction in air. A point source of light is reflected from a concave mirror and focused onto the edge of a razor blade, which is mounted in front of the camera. Light refracted near the mirror and intercepted by the blade gives the illusion of a shadow.Seen here are the heated gases from a candle flame and a hair dryer, helium gas, and sulfur hexafluoride gas.For more information on our setup please seehttp://sciencedemonstrations.fas.harvard.edu/presentations/schlieren-opticsNote that this version of the setup uses a white LED flashlight instead of an automotive light bulb.Thanks for watching!
Jumping Wire Harvard Natural Sciences Lecture Demonstrations 2023-03-02 | A current-carrying wire passing between the poles of a large magnet experiences a force perpendicular to both the magnetic field and to the current direction. On a microscopic scale, the moving charges in the wire experience a Lorentz force due to the external magnetic field. On a macroscopic scale, we see an interaction of current and magnetic field. The battery is a 12 Volt gel cell. The wires have a total resistance of about 0.1 Ohms. The magnet is about 0.3 Tesla between the poles.For more details about our setup, see https://sciencedemonstrations.fas.harvard.edu/presentations/jumping-wire
Circular Motion vs Mass on Spring Harvard Natural Sciences Lecture Demonstrations 2021-08-24 | Simultaneous shadow projection of circular motion and an oscillating mass on a spring. We see that the vertical component of the circular motion is identical to that of the vertically oscillating mass. This simple harmonic motion can be mathematically modeled over time with sinusoidal functions.The 8 cm diameter plastic ball is mounted near the edge of a 46 cm diameter disk and is driven by a Bodine Electric Co type NS1-33R speed reducer motor. The disk is cut from 1/8" thick masonite. The mass weighs 20 N, and was fortunately paired with a spring to match the speed of the motor. Illumination is provided by a Kodak slide projector.Thanks for watching!
Infrared Camera Harvard Natural Sciences Lecture Demonstrations 2021-08-17 | We use an infrared camera to look at objects of different temperatures (ice, hot water, candle flame). We then look at objects made of different materials (acrylic, plastic trash bag, aluminum plate) to see which ones are transparent in the infrared vs the visible part of the spectrum. Finally, liquid nitrogen is poured over a cup of hot water.The camera we use is a FLIR E-95, which can detect wavelengths in the 7.5-14 micron range. Never attempt to drink liquid nitrogen!
5 Minutes of Lava Lamp Convection in 4K Harvard Natural Sciences Lecture Demonstrations 2021-08-07 | Five minutes of superfluous lava lamp footage. The fixture is about 27 inches tall from top to bottom, with the glass portion extending 14 inches vertically. Inside the glass container is a mix of colored wax and water, which is heated and illuminated from below by a 100W incandescent bulb and a pair of 25W heating elements in the base. At room temperature the wax is slightly more dense than the water, but when it's heated it expands and becomes more buoyant, causing it to float up toward the top, where it cools and loses its buoyancy. This convection cycle is thought to model the behavior of hot magma beneath the surface of the Earth.Thanks for watching!
Flame Tests of Metals Harvard Natural Sciences Lecture Demonstrations 2021-07-16 | Qualitative demonstration of how salts of various metals—sodium, lithium, potassium, calcium, strontium, barium, and copper—emit characteristic colors when burned in a flame. We can analyze the component colors by placing a 500 lines/cm diffraction film in front of the camera lens. Notice that some elements are mostly monochromatic (sodium, for example) while others emit a range of colors (calcium, etc). A slightly more quantitative analysis would incorporate a slit between the flame and the diffraction grating to make the profiles of the emissions narrower and more precise.Thanks for watching!
Nylon Synthesis Harvard Natural Sciences Lecture Demonstrations 2021-06-08 | A classic science demonstration of two-component polymerization, nylon 66 (also known as "nylon 6,6") is pulled from the interface of two solutions: Hexamethyldiamine in 0.5M sodium hydroxide solution is the lower layer, and adipoyl chloride in cyclohexane is the upper layer. The two compounds react at the interface, making a polymer that can be pulled out as a thread that keeps forming until one or both of the solutions are depleted. Check out en.wikipedia.org/wiki/Nylon for the creative—and ultimately tragic—Harvard connection.
Metals in Acid Harvard Natural Sciences Lecture Demonstrations 2021-05-26 | Curly strips of zinc and magnesium are dropped into 2M hydrochloric acid, and bubbles of hydrogen gas are observed as a result of the reactions.For more details on our setup, see https://sciencedemonstrations.fas.harvard.edu/presentations/metals-acidThanks for watching!
Limiting Reagent Vinegar or Baking Soda? Harvard Natural Sciences Lecture Demonstrations 2021-05-24 | Vinegar and two different amounts of baking soda in plastic soda bottles with balloons.Two 500ml soda bottles of the same make, split a bottle of vinegar between them.11" balloons are pre-inflated with dry air, with care taken not to stretch the neck of the balloon. Into the balloons with a funnel go one, two teaspoons of baking soda. With 250 ml of vinegar, that's like six liters of gas potential if one carbon dioxide comes from one acid hydrogen ion.For more details on how we set up and do this demo, seehttps://sciencedemonstrations.fas.harvard.edu/presentations/limiting-reagent-vinegar-or-baking-sodaThanks for watching!
Polarization by Scattering, and Fishtank Sunset Harvard Natural Sciences Lecture Demonstrations 2021-05-21 | Simulation of atmospheric scattering and polarization of sunlight using a slide projector and an aquarium containing milky water. In the first part of the demo, we use an angled mirror to show the effect of a polarizer on light scattered from the side of the tank vs from the top of it. In the second part, we show how Rayleigh scattering makes the sky blue and sunsets red by gradually adding more milk to the water in the tank.For more details on our setup, seehttps://sciencedemonstrations.fas.harvard.edu/presentations/polarization-scatteringThanks for watching!
Tower of Spectra Harvard Natural Sciences Lecture Demonstrations 2021-05-13 | We compare the visible spectra of hydrogen, helium, and neon gas discharge tubes. For comparison we also have an incandescent tungsten filament. Notice that the gases in the tubes emit light only in discrete colors, while the incandescent filament emits light in a continuous range. The spectra of each element is like a unique fingerprint that describes its quantum nature, and has long been used by astronomers to deduce the composition of stars and nebulae billions (and billions) of miles away. For more photos of our setup, seehttps://sciencedemonstrations.fas.harvard.edu/presentations/tower-spectraThanks for watching!
pH Buffer Solution Harvard Natural Sciences Lecture Demonstrations 2021-04-07 | We have four containers with universal indicator: Two of them are mixed with distilled water, the other two mixed with a buffer solution of ammonia and vinegar. We compare the pH changes when we add dropper-fulls of 1M NaOH and HCl to the dishes. We see that the water changes pH very easily, while the buffer solution is much more resistant. Always wear proper PPE when working with chemicals!
Dry Ice in Universal Indicator Harvard Natural Sciences Lecture Demonstrations 2021-03-30 | The effect of carbon dioxide on the pH level of water is demonstrated by dropping a couple chunks of dry ice into a column of universal indicator. The indicators in the two columns are initially set up to be basic, so that we may see the effect of the dry ice more clearly. When a few dropper-fulls HCl 1M is added, the color changes and persists as orange; when NaOH 1M is added, the color momentarily changes back to purple, but then quickly goes back to yellow as more of the dry ice sublimates.Always wear proper PPE when working with chemicals!
Red Cabbage Indicator Harvard Natural Sciences Lecture Demonstrations 2021-03-30 | A universal indicator made from cabbage changes color when acids (vinegar) and bases (ammonia) are added to it. This is a simple experiment that can be done at home with stuff you can buy at your local market.
Doppler Effect with Car Horn Harvard Natural Sciences Lecture Demonstrations 2021-03-10 | The Doppler Effect—the sound of coming and going: When a source of sound is moving toward you, successive wavefronts arrive more frequently. You perceive this increase in frequency as a higher tone. Conversely, if the source of sound is moving away from you, the time between wavefronts reaching you is a little longer and this decrease in frequency is perceived as a lower tone.
Double Fire Tornado Yule Log (30 minute loop) Harvard Natural Sciences Lecture Demonstrations 2020-12-10 | Happy holidays! Two differently colored flames rotate on a turntable with a tubular screen attached to it. The hot air from the flame rises up the tube, drawing fresh air that comes in from the sides to replace it. As air moves into the tube, the rotating screen deflects it slightly off-axis. As the air gets closer to the flame, conservation of angular momentum causes it to spin faster, forming a vortex characteristic of a tornado.
Radio Wave Properties: Electric and Magnetic Dipole Antennae Harvard Natural Sciences Lecture Demonstrations 2020-11-18 | An HP model 3200B VHF Oscillator and ENI model 5100-L NMR RF Broadband Power Amplifier provide a 300 MHz signal to a half-wave dipole antenna. The voltage variation along the length of the dipole transmitting antenna is made evident by touching one end of a 8-Watt fluorescent lamp. A copper rod of the same length as the transmitting antenna is used to show a similar standing wave in voltage along it. A second receiver antenna with an incandescent bulb wired in the middle shows the polarization and shape of the radiation pattern emitted by the transmitter. Finally, a loop antenna is used to show the polarization of the magnetic component of the electromagnetic wave.For lots more details on our setup, see https://sciencedemonstrations.fas.harvard.edu/presentations/radio-wave-properties
Photochemical Reaction of Hydrogen and Chlorine Harvard Natural Sciences Lecture Demonstrations 2020-10-09 | Different colors of LED light illuminate a small corked test tube of hydrogen and chlorine gas with no reaction; ultraviolet light causes an explosion that shoots the cork across the room. The gas mixture is made by the electrolysis of hydrochloric acid 8M. A water bath allows for filling the tubes under water. The tubes are quartz. References* Richard Schwenz and Lynn Geiger. "Photon-Initiated Hydrogen-Chlorine Reaction." Journal of Chemical Education 76.4 (1999): 470.* Shakhashiri, Bassam Z. "Chemical Demonstrations: A Handbook for Teachers of Chemistry." Madison: The University of Wisconsin Press, 1983. ( http://books.google.com/books?id=0rx6Cjx_l-AC&lpg=PP1&pg=PA121#v=onepage&q&f=false)
55 Gallon Drum Collapse Harvard Natural Sciences Lecture Demonstrations 2020-09-15 | When the air inside a 55 gallon steel drum is pumped out, we see the weight of the atmosphere push inward with 101 kPa of pressure. The top and bottom of the drum has a radius of about 30 centimeters, and it is about 1 meter tall. This means the atmosphere pushes down on the top of the drum with about 6,500 pounds of force! We leave the calculation of the force on the sides as an exercise to the student.We pump on the drum with a Varian SD-200 vacuum pump. Usually the initial collapse will occur after a minute or two. The drum seen here actually underwent initial collapse after 35 seconds of pumping; the footage was edited to make it more watchable.For more details on our setup, see https://sciencedemonstrations.fas.harvard.edu/presentations/55-gallon-drum
Chaotic Waterwheel Harvard Natural Sciences Lecture Demonstrations 2020-05-13 | A waterwheel with leaky buckets undergoes chaotic motion. Our wheel is about 1 meter in diameter and was fabricated with wood in our shop. The little buckets are citronella candle holders with ¼” holes drilled out of the bottom. The sump pump was purchased from the local hardware store. A ball valve at the faucet regulates the water flow. The wheel and pump both sit in a concrete mixing tub. In nature, chaotic behavior readily occurs in turbulent flows and in large-scale weather patterns, but scaling these systems to a laboratory or classroom setting is far from trivial. The idea of building a waterwheel as a discrete, mechanical example of a chaotic system was proposed and realized by Willem Malkus, Louis Howard, and Ruby Krishnamurti in the early 1970s. According to Edward Lorenz, their original design “was a precision instrument, suitable for controlled laboratory experiments.” Our design is simpler and geared more towards pedagogical impact than experimental fidelity, but we think you will find it charming and instructive nonetheless. For more details on our setup, including links to download some of the clips of the wheel in motion, see https://sciencedemonstrations.fas.harvard.edu/presentations/chaotic-waterwheel
Poiseuilles Law (16 tubes vs 1 tube) Harvard Natural Sciences Lecture Demonstrations 2020-04-06 | The laminar flow rate of an incompressible fluid along a pipe is proportional to the fourth power of the pipe's radius. To test this idea, we'll show that you need sixteen tubes to pass as much water as one tube with twice their diameter.We have two tanks of equal dimension next to each other. The first tank has a row of 16 tubes inserted near the bottom, all of equal length, and are 0.101" in diameter. The second tank has a single tube inserted with nearly twice the diameter (0.207") and equal length as the others. An equal amount of water is added to the tanks, so that the pressure difference between the ends of all 17 tubes is the same. With the fluid viscosity, pipe length, and pressure difference the same among all the tubes, the only difference is their radii.The valves to all the tubes are opened simultaneously, and we see that the flow rates are very nearly equal--even over the course of several minutes. (The difference in water levels seen at the end of the experiment was measured to be roughly 5 percent.)For more details on our setup, see https://sciencedemonstrations.fas.harvard.edu/presentations/poiseuilles-law
Total Internal Reflection in Water Bucket of Light Harvard Natural Sciences Lecture Demonstrations 2020-04-01 | A beam of laser light can be trapped inside a stream of water by suffering total internal reflection—the aquatic equivalent of a fiber optic cable. In our setup we have a 2-liter soda bottle with a hole cut into the side. The bottle is filled with water and a few drops of milk. A 5 mW HeNe laser is brought up to the side of the bottle, so that the beam exits the bottle via the hole. The laser light undergoes total internal reflection as the stream of water falls into the bucket in a cohesive stream.Some of you may notice that the white bucket glows with the same color as the laser light, even after the water has stopped flowing into it! How can this be? Does the light keep reflecting around inside the bucket? Did we somehow find a way to violate conservation of energy? This part of the demo is a trick, of course: a network of red LEDs line the bottom of the bucket! For more details on how we set up this demo, seehttps://sciencedemonstrations.fas.harvard.edu/presentations/bucket-light
Launch Lab, a conservation of momentum experiment Harvard Natural Sciences Lecture Demonstrations 2020-03-31 | Nils gives a demonstration and description of the Launch Lab. The experiment is a variation on a ballistic pendulum--instead of a projectile colliding with the pendulum, it is ejected from it. The platform consists of a section of Masonite, a clothes pin, a rubber band, a thread, a match, and is suspended with fishing line. The projectiles are stainless steel and (low density) wood spheres. Students can use a video camera to track the motion of the system after the stored energy of the rubber band is released.The video clips used in this video are in 240 fps and can be downloaded from heredrive.google.com/drive/folders/14uo9H39-arDLdm4ZrjwhE60ejy_pHzsy?usp=sharingThe platform is roughly 30 cm long. The steel ball is roughly 200 grams.
Blackbody Radiation Oven Harvard Natural Sciences Lecture Demonstrations 2020-03-23 | Blackbody radiators in thermal equilibrium should emit the same spectrum of radiation; inside an oven at high temperature, objects should appear with the same color, whatever their material.A small ball of iron and a chunk of brick are placed inside a muffle furnace that has been preheated to about 1000 C. The interior walls and heating elements of the hot furnace have a bright, yellowish glow to them. The samples of iron and brick, on the other hand, are at room temperature (about 25 C) when they are first inserted, and so their brightness and color make them stand out against the hot background. The samples are heated for about 30 minutes, which is enough time for both of them to reach the same temperature as the interior of the furnace. When the door is opened, we see that the samples glow with nearly equal intensity and color as their surroundings! When the samples are removed from the furnace, we see that they both start out at nearly the same brightness and color. As they cool they become less bright, and the colors they emit gradually move toward the red part of the visible spectrum.Seen here is a Blue M Electric Company Lab-Heat M-10A muffle furnace. For more details on how we do this demo, see https://sciencedemonstrations.fas.harvard.edu/presentations/black-body-radiation-oven
Convection Cell Sea Breeze Visualization Harvard Natural Sciences Lecture Demonstrations 2020-03-11 | Convection cell demonstration narrated by Steven Wofsy for E-PSCI 338 February 2020. A heating element in the bottom-right side of a tank of water causes convective circulation. The warm water above the heater rises up to the surface and moves over to the left side of the tank, where it starts to cool. Losing buoyancy as it cools, the water gradually returns to the bottom, where it completes the cycle by being drawn back into contact with the heater.One can draw an analogy with this demo and onshore breezes that occur along the coast on hot summer days. In that case, air heated by land rises up and is replaced by cooler air moving in from over the ocean. The tank was custom built at Harvard Bio Labs Machine Shop in Cambridge, MA; it is about 14" x 10" x 2" and is made out of acrylic. The heater is a 125W Cenco Knife Type Immersion Heater connected to a Variac. About 20 drops of concentrated rheoscopic fluid were added to distilled water.
What Does Acoustic Interference Look Like? Harvard Natural Sciences Lecture Demonstrations 2019-10-18 | We use the strobing schlieren effect to visualize acoustic interference between two 28 kHz sound waves. Recognizing where constructive interference must take place allows us to interpret bright bands of light that appear in the continuously illuminated schlieren image.Special thanks to Dr. A. Klales, who first suggested we try this experiment, and also thanks to J. Peidle, for showing us how to externally trigger the strobing LED!
Visualizing Ultrasound with Schlieren Optics Part III Harvard Natural Sciences Lecture Demonstrations 2018-06-12 | Part 3 of 3. We combine the stroboscopic effect with the use of color filters in our schlieren optics setup to visualize the changes in air pressure that occur in a standing wave created by an ultrasonic transducer (driven at 28 kHz) and a reflecting glass plate. As a finale, we levitate small Styrofoam balls in the pressure antinodes.Without the color filters, the brightness of the schlieren image only gives us information about the magnitude of the pressure changes in the standing wave. We can now use the color information to tell us whether the pressure is increasing or decreasing. Each colored band is a pressure antinode that is oscillating between high and low pressure.The order of the color bands in the standing wave depends on the relative phases of the strobe light and the transducer. Although we do not show it here, shifting the phase of the strobing light source by 180 degrees causes the colors in the standing wave to reverse.The color filters we use here are Kodak Wratten 2 color filter #29 (red) and #61 (green).More information about our schlieren optics set-up and how it works can be found on our Science Demonstration website: https://sciencedemonstrations.fas.harvard.edu/presentations/schlieren-opticsSafety Note: Although 28 kHz is beyond the range of human hearing, ear protection should be worn whenever attempting this experiment to avoid damaging vibrations in parts of the ear. Any high-pitched whines you hear in this video are not dangerous.
Visualizing Ultrasound with Schlieren Optics Part II Harvard Natural Sciences Lecture Demonstrations 2018-06-12 | Part 2 of 3. We use our strobing schlieren system to look at diffraction and standing wave patterns in air created by an ultrasonic transducer (driven at 28 kHz) and a reflecting glass plate.More information about our schlieren optics set-up and how it works can be found on our website: https://sciencedemonstrations.fas.harvard.edu/presentations/schlieren-opticsSafety Note: Although 28 kHz is beyond the range of human hearing, ear protection should be worn whenever attempting this experiment to avoid damaging vibrations in parts of the ear. Any high-pitched whines you hear in this video are not dangerous.
Visualizing Ultrasound with Schlieren Optics Part I Harvard Natural Sciences Lecture Demonstrations 2018-06-12 | Part 1 of 3. We use a schlieren optics system with a strobing light source to visualize ultrasonic waves emitted by a transducer driven at a frequency of 28 kHz.Images employing schlieren optics are very sensitive to changes in the density of air. Since sound waves are pressure waves, and pressure variations result in density gradients, it stands to reason that one should be able to image sound waves traveling through the air. Unfortunately, the waves move at the speed of sound (343 meters per second), which makes it difficult for us to see them. With stroboscopic animation, we can slow down the apparent motion of the sound waves.Some of you probably wonder whether this experiment would work with audible sound waves at, say, 1 kHz (about 34 centimeters in wavelength). Not only is that wavelength much bigger than our mirror, but it turns out that our optical setup is not sensitive enough to see the density gradients formed by 1 kHz sound (at least not at a Sound Pressure Level that is less than that of a jet engine). We can, however, see the the density gradients formed by 28 kHz sound waves, which have a wavelength of about 1.2 centimeters. We use here an 18" diameter, f/4.3 concave mirror that we salvaged from a spectrometer. The light block is a size 7 piano wire, mounted at 45 degrees with respect to the vertical on a lens holder. The light source is an Engin LZ4-00CW08 cool white LED. The transducer is an American Piezo 28 kHz Cleaning Transducer model #90-4040 and is driven by a Samson Servo 120 power amplifier.More information about our schlieren optics setup and how it works can be found on our Science Demonstrations website: https://sciencedemonstrations.fas.harvard.edu/presentations/schlieren-opticsSafety Note: Although 28 kHz is beyond the range of human hearing, ear protection should be worn whenever attempting this experiment to avoid damaging vibrations in parts of the ear. Any high-pitched whines you hear in this video are not dangerous.
Coanda Effect Harvard Natural Sciences Lecture Demonstrations 2017-06-07 | Fluids flowing near a surface tend to follow the shape of the surface. Using Schlieren optics, we can see this behavior. It is known as the Coanda Effect and its explanation depends on viscosity, the frictional forces between the molecules of a fluid (be it liquid or gas). The Coanda effect is the culprit behind many everyday incidents as well as more esoteric phenomena, such has levitating a ball in a stream of air.Details of our Schlieren optics set-up can be found on our website: https://sciencedemonstrations.fas.harvard.edu/presentations/schlieren-optics
Acoustic Standing Waves and the Levitation of Small Objects Harvard Natural Sciences Lecture Demonstrations 2017-02-23 | Acoustic levitation meets schlieren imaging: By reflecting a sound wave back onto itself, one can secure a standing wave if the distance between the source of the sound and the reflector is equal to an integral number of half wavelengths. In this demonstration we use 28 kHz ultrasound whose wavelength in air is 1.2 cm. The objects are small Styrofoam spheres, roughly 4 mm in diameter and 1 mg of mass.Images employing schlieren optics are very sensitive to changes in the density of air, and these changes refract light into the camera. Note that the little spheres settle down where there are bright bands of light. The bright bands of light in the schlieren images are known to be the result of either increasing or decreasing air pressure with respect to vertical position—in other words, the pressure nodes. For an excellent writeup by David P. Jackson and Ming-Hua Chang on the mechanics of acoustic levitation, see American Journal of Physics 89, 383 (2021); doi.org/10.1119/10.0002764For more information on our schlieren optics set-up, seehttp://sciencedemonstrations.fas.harvard.edu/presentations/schlieren-opticsAlthough 28 kHz is beyond the range of human hearing, ear protection should be worn whenever attempting this experiment to avoid damaging vibrations in parts of the ear. The sound you hear in this video is not ultrasound but rather a subharmonic and is not dangerous to your ears.
Fire Tornado Harvard Natural Sciences Lecture Demonstrations 2017-01-25 | A story of one man's love of a fire tornado demonstration. A small metal container sits in the center of a 13" diameter turntable. Bending and clamping a brass screen (10 wires per inch) around the perimeter of the turntable forms a 36" tall cylinder. Isopropyl alcohol in the small metal container is lit, and the turntable is set in motion.As the surrounding air is drawn to the flame, it is deflected from the center of the turntable as it passes through the openings in the screen. The resulting angular momentum of the gases helps to form a tall, twisting column of fire.FIRE IS HOT!
Vacuum Cannon Harvard Natural Sciences Lecture Demonstrations 2016-09-02 | High speed footage of a ping pong ball, propelled by air rushing into an evacuated tube, penetrating three empty soda cans. The PVC tube is 8 feet long and 1.5 inches in diameter, with a layer of mylar sealing both ends. The ball accelerates down the tube from rest to over 650 mph, easily breaking through the mylar and the soda cans at the other end before disintegrating.For more information on our setup, seehttp://sciencedemonstrations.fas.harvard.edu/presentations/vacuum-cannon
Sodium Absorption Lines Harvard Natural Sciences Lecture Demonstrations 2016-06-09 | Burning of sodium bicarbonate in Bunsen flame produces sodium absorption lines in continuous spectrum. Sodium 'D' line absorption shows up as a black line in the yellow of a continuous spectrum. Good as a simulation of the sodium portion of the Fraunhoffer absorption spectrum caused by atoms in the solar atmosphere; it does not however, resolve the 5890/5896Å doublet.For more details, seehttp://sciencedemonstrations.fas.harvard.edu/presentations/sodium-absorption
Reverse Sprinkler Harvard Natural Sciences Lecture Demonstrations 2016-01-15 | Which direction does a lawn sprinkler spin if fluid enters the nozzle rather than being expelled from it? Inspired by Richard Feynman's story in his 1985 book "Surely You're Joking, Mr. Feynman."For more information on our setup and references for further study, see http://sciencedemonstrations.fas.harvard.edu/presentations/reverse-sprinkler
Meissner Effect Harvard Natural Sciences Lecture Demonstrations 2015-08-07 | A permanent magnet begins to hover above a ceramic material as it cools and transitions to a superconducting state; the magnet remains aloft until the ceramic warms above a critical temperature.The ceramic material is a 25mm disc of yttrium barium copper oxide (YBa2Cu3O7, also commonly referred to as "YBCO”). The YBCO has a critical temperature of 90K and is cooled with liquid nitrogen, which boils at 77K. The magnet is just under 5mm per side and weighs about 0.8 grams.The magnet is able to levitate due to its interaction with persistent electric currents that expel external magnetic field from the interior of the superconducting YBCO. (The details of this interaction are complicated, and cannot be fully explained using classical physics.)For more details on our setup and references for further study, see http://sciencedemonstrations.fas.harvard.edu/presentations/meissner-effectAlso check out this video from the Annenberg Foundation on high-temperature superconductor research http://www.learner.org/courses/physics/video/vid_byunit.html?unit=6&vidNum=1
Mousetrap Fission Setup Harvard Natural Sciences Lecture Demonstrations 2015-02-26 | Woflgang and Allen quickly and efficiently prepare the Mousetrap Fission demo for Robert Kirshner's The Energetic Universe course on February 26, 2015. The demo consists of 110 mousetraps armed with ping-pong balls; the demonstrator drops a single ball from above to initiate an event similar to a chain reaction.For more details on this demo see http://sciencedemonstrations.fas.harvard.edu/presentations/nuclear-fission
Thin Film Interference (part 2) Harvard Natural Sciences Lecture Demonstrations 2014-08-08 | Close up of a thin film of soapy water that is vertically suspended across a 19 cm diameter plastic ring and illuminated with white light. Gravity pulls down on the film to make it much thinner in the top section of the ring than in the bottom section. Light reflecting from the front surface of the thin film is able to interfere with light reflecting off of the back, resulting in different reflected colors from different film thicknesses. For example, where the film thickness causes destructive interference for blue light but constructive interference for green and red, we perceive the color yellow from the reflection of white light. Eventually the film at the top of the ring becomes so thin that destructive interference occurs for most of the visible wavelengths, resulting in no reflection of visible light—the film is rendered completely transparent and all we see is the black background.Starting at about 1:12, the colors seen in the upper section of the ring are roughly what we would expect from a linearly increasing film thickness. Meanwhile in the lower section the thickness is changing in a more complicated way, and the colors appear washed out.The soap film shown here consists of 2/3 cup of Dawn liquid dishwashing soap, 3 tablespoons of glycerol, and 1 gallon of water. We guess that the average index of refraction of the solution is close to that of water (about 1.33). The footage was taken July 16, 2014—the third consecutive day of rain and high humidity in Cambridge, MA. The light source is a portable fluorescent light box with a color temperature of between 4500 and 5000 Kelvin. The camera used is a Blackmagic Cinema MFT with a Vivitar Auto Wide Angle 35 mm lens. The footage was shot at 800 ASA in CinemaDNG RAW 2.5K and color corrected using DaVinci Resolve 10 Lite.For further study, seehttp://sciencedemonstrations.fas.harvard.edu/presentations/thin-film-interferencePhysical Science Study Committee, Physics, (D.C. Heath, 1960) Chapt. 19 sect. 9 "Interference in Thin Films.”Leslie J. Atkins, Richard C. Elliott, Investigating thin film interference with a digital camera. Am. J. Phys. 78, 1248 (2010); http://scitation.aip.org/content/aapt/journal/ajp/78/12/10.1119/1.3490011#http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/soapfilm.html
Thin Film Interference (part 1) Harvard Natural Sciences Lecture Demonstrations 2014-08-08 | Wide shot of a thin film of soapy water that is vertically suspended across a 19 cm diameter plastic ring and illuminated with white light. Gravity pulls down on the film to make it much thinner in the top section of the ring than in the bottom section. Light reflecting from the front surface of the thin film is able to interfere with light reflecting off of the back, resulting in different reflected colors from different film thicknesses. For example, where the film thickness causes destructive interference for blue light but constructive interference for green and red, we perceive the color yellow from the reflection of white light. Eventually the film at the top of the ring becomes so thin that destructive interference occurs for most of the visible wavelengths, resulting in no reflection of visible light—the film is rendered completely transparent and all we see is the black background.At about 1:20, the colors seen in the upper section of the ring are roughly what we would expect from a linearly increasing film thickness. Meanwhile in the lower section the thickness is changing in a more complicated way, and the colors appear washed out.The soap film shown here consists of 2/3 cup of Dawn liquid dishwashing soap, 3 tablespoons of glycerol, and 1 gallon of water. We guess that the average index of refraction of the solution is close to that of water (about 1.33). The footage was taken July 16, 2014—the third consecutive day of rain and high humidity in Cambridge, MA. The light source is a portable fluorescent light box with a color temperature of between 4500 and 5000 Kelvin. The camera used is a Blackmagic Cinema MFT with an Angenieux 20-80 mm zoom lens. The footage was shot at 800 ASA in CinemaDNG RAW 2.5K and color corrected using DaVinci Resolve 10 Lite.For further study, seehttp://sciencedemonstrations.fas.harvard.edu/presentations/thin-film-interferencePhysical Science Study Committee, Physics, (D.C. Heath, 1960) Chapt. 19 sect. 9 "Interference in Thin Films.”Leslie J. Atkins, Richard C. Elliott, Investigating thin film interference with a digital camera. Am. J. Phys. 78, 1248 (2010); http://scitation.aip.org/content/aapt/journal/ajp/78/12/10.1119/1.3490011#http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/soapfilm.html
Cloud Chamber Harvard Natural Sciences Lecture Demonstrations 2014-03-06 | The trajectories of individual charged particles leave behind cloudy trails as they ionize the cooled, supersaturated air-alcohol vapor inside this diffusion cloud chamber. Alpha particles from the radioactive decay of an inserted 2% thorium alloy rod form dense condensation trails nearby. Farther from the rod (beyond 10 cm or so) various types of charged particles leave evidence of their activity, including alpha particles (dense tracks, perhaps from the decay of radon isotopes), muons and energetic electrons (faint, seemingly straight tracks), and relatively low-energy electrons and beta particles (faint, tangled tracks).This movie shows a basic, qualitative demonstration of the presence of subatomic particles; techniques to more accurately identify and measure individual subatomic particles are possible with this apparatus.The cloud chamber was first developed by C.T.R. Wilson around the turn of the 20th century to study optical phenomena associated with mist and clouds (he received the Nobel Prize in 1927). When charged particles ionize a supersaturated vapor, a trail of ions is left in the path of the particles. The ions act as condensation nuclei for the alcohol to condense on, and a thin line of fine droplets is formed in the path of each particle.The range of the alpha particles from the thorium source is about 4 cm. As the alpha traverses its path, it slows down gradually and becomes more heavily ionizing by virtue of the fact that it spends more time in the vicinity of air molecules in its path. Evidence for this can be seen by observing that the tracks become denser with increasing distance from the source. This particular diffusion cloud chamber was built by Supersaturated Environments of Madison, WI (http://www.cloudchambers.com). Dry ice pellets under the chamber floor help to create a steep temperature gradient from top to bottom. Felt strips along the top of the chamber are soaked with 95% ethanol. The viewing area is 51 square centimeters, with inscribed "+" marks every 10 centimeters. The special slide inserted into the Kodak Ektagraphic III projector saves the viewing audience from unnecessary glare.REFERENCES* W. Gentner "An Atlas of Typical Expansion Chamber Photographs" Pergamon Press, 1954.* E.W. Cowan, "Continuously Sensitive Diffusion Cloud Chambers" Review of Scientific Instruments 21, 991 (1950)* R. Cases, E. Ross, J. Zuniga "Measuring Radon Concentration in Air Using a Diffusion Cloud Chamber" Am. J. Phys. 79, 903 (2011)For some more details on our setup see:http://sciencedemonstrations.fas.harvard.edu/presentations/cloud-chamber
Relativity Train Harvard Natural Sciences Lecture Demonstrations 2013-09-20 | The Relativity Train is a realization of the famous Einstein thought experiments involving traveling trains carrying clocks and meter sticks. The demonstration is used to show how the preservation of the postulated constancy of physical laws and the speed of light in all inertial frames requires length contraction and time dilation in the train frame relative to the lab frame of reference. The demonstration is, of course, not a real experiment but rather a visual means of showing (without using any equations) how length contraction and time dilation are necessary consequences of Einstein's two assumptions.For more references and info on our setup seehttp://sciencedemonstrations.fas.harvard.edu/presentations/relativity-trainFor more information on Prof Papaliolios see http://www.news.harvard.edu/gazette/2004/05.13/18-mm.html
Shoot the Monkey Harvard Natural Sciences Lecture Demonstrations 2013-08-22 | This is a demonstration of the independence of the horizontal and vertical components of the velocity of a projectile. For more details see http://sciencedemonstrations.fas.harvard.edu/presentations/shoot-monkeyIn this video we see the spring-powered gun shooting the same steel ball bearing with two different initial velocities in an attempt to show that the initial speed of the ball does not matter. The shots at 0:51, 1:00, and 1:09 are close to the maximum speed (roughly 13 m/s), while the shots at 1:18, 1:27, and 1:34 are close to the minimum (roughly 9 m/s). All other parameters remain the same for all trials; the horizontal distance is about 6.9 meters, and the launch angle is about 23 degrees above the horizontal.
Rotating Saddle Harvard Natural Sciences Lecture Demonstrations 2013-01-24 | A playground ball finds stability in a saddle when the saddle is rotating at the proper speed.Mechanical analog of a "Paul Trap" particle confinement—a ball is trapped in a time-varying quadrupole gravitational potential. A large saddle shape (attached to a plywood disk) is mounted on a multi-purpose turntable. The saddle shape is essentially a quadrupole gravitational potential. Rotation of this potential subjects the ball to an alternating repulsive and attractive potential, much like the time-varying electric quadrupole potential of a Paul Trap used in trapping single ions or electrons.The plastic ball used here is about 25 cm in diameter and was purchased at a toy store. The saddle consists of a rubber sheet and fiberglass, and was hand-made with help from Justin Georgi. The turntable is driven at about 110 rpm with a DC motor. We have observed this ball at this speed remaining stable for over 2 hours.Slow motion footage recorded at 240 fps with a Casio EX-FH25. Thanks to Rob for letting us use the camera.For more information on our demo and references for further study see http://sciencedemonstrations.fas.harvard.edu/presentations/rotating-saddle
Inverted Pendulum Harvard Natural Sciences Lecture Demonstrations 2012-12-20 | A physical pendulum finds stability in its inverted position when driven at the proper frequency and amplitude combination.The physical pendulum seen here is mounted on a ball-bearing pivot and can rotate 360 degrees; the pivot is driven at about 50 Hz with an amplitude of about 1 cm (3/4" per stroke) by a Sears Craftsman Auto Scroller Saw (model 315.172090); the length is 45 cm and the center of mass is slightly above 15 cm from the pivot; the rotational inertia is roughly 4x10^(-4) kg*m^2; the mass is about 100 grams.For more details and references for further study see:http://sciencedemonstrations.fas.harvard.edu/presentations/inverted-pendulumShot in 24 and 300 fps. Thanks to Rob, Fu, and Daniel for their help.
Vortex Shedding in Water Harvard Natural Sciences Lecture Demonstrations 2012-06-22 | Wolfgang uses a pendulum partially immersed in a makeshift flow tank to show us the effect of vortex shedding on a small object.When fluid flows around a cylindrical object, there is a range of flow velocities for which a von Karman vortex street is formed. The shedding of these vortices imparts a small, periodic force on the object. Here the object is a cylinder attached to a physical pendulum whose frequency of oscillation is adjustable. The end of the cylinder is submerged in flowing water. When the frequency of the pendulum is adjusted to match the frequency of vortex shedding, the cylinder swings transverse to the direction of flow with a peak-to-peak amplitude of a few centimeters.For more details on our setup as well as references for further study see http://sciencedemonstrations.fas.harvard.edu/presentations/vortex-shedding
Paramagnetism of Oxygen Harvard Natural Sciences Lecture Demonstrations 2012-03-16 | Oxygen gas is condensed into liquid form and then poured between the poles of a strong magnet so we can observe its paramagnetic properties.We send O2 gas through a copper coil, which is then immersed in about 2 liters of liquid nitrogen (77 Kelvin, or minus 196 degrees Celsius). As the O2 travels through the coil it loses enough heat to change from a gas to a liquid, and that liquid is collected in a small pre-cooled Dewar. Liquid nitrogen is poured between the poles of the permanent magnet, but since its diamagnetic properties lead to only a very weak interaction with the field, it just sloshes through as if it were water. The liquid oxygen, on the other hand, sticks between the poles of the magnet until it boils away. Because the oxygen molecule has an electronic structure that favors the non-cancellation of two of the electron spins, its net magnetic moment is free to point in the direction of an external magnetic field (just as a compass needle does). When enough of these moments are aligned, the material as a whole behaves like a single magnet. At room temperature only a small fraction of the moments are able to line up perfectly with the external field, but when oxygen is cooled and condensed into a liquid the effect is more noticeable.For more details on our setup see:http://sciencedemonstrations.fas.harvard.edu/presentations/paramagnetism-oxygenLike us on Facebook! http://www.facebook.com/NatSciDemos
Conductivity of Glass Harvard Natural Sciences Lecture Demonstrations 2012-01-05 | Insulating glass becomes a conductor of electricity when heated with a blowtorch.Two ceramic lightbulb sockets are wired in series to a household AC power cord. When two incandescent bulbs of the same Wattage rating are screwed into the sockets and the cord is plugged in, they both pass the same amount of current and so they both light with the same intensity. When one bulb is unscrewed, the circuit is broken and the other bulb goes out. If we can replace the missing bulb with a conductive material, the circuit will once more be complete and the remaining bulb will light again.For more details on our setup, see http://sciencedemonstrations.fas.harvard.edu/presentations/conductivity-glass
Coffee Mug on String Harvard Natural Sciences Lecture Demonstrations 2011-12-21 | Angular momentum helps save a red ceramic coffee mug from certain destruction. We used some string, two stolen mugs, and two Ticonderoga Dixon No. 2 pencils. Please do attempt.For more details on our setup see http://sciencedemonstrations.fas.harvard.edu/presentations/coffee-mug-stringSpecial thanks to Rob and Nils.Like us on Facebook!facebook.com/NatSciDemos
Balancing Forks Harvard Natural Sciences Lecture Demonstrations 2011-12-20 | Two metal forks, a cork, and a matchstick balance on the lip of a glass. The center of mass of the fork-cork-match system is well below the pivot point, so balance is able to return after small perturbations. Please be careful when playing with matches.For more details on this setup, seehttp://sciencedemonstrations.fas.harvard.edu/presentations/balancing-forks
The Wineglass That Wont Break Harvard Natural Sciences Lecture Demonstrations 2011-11-23 | (Warning: obnoxious sound) For some reason I can't get this wineglass to break. It's an Oregon Balloon Wine 22oz. (made in Slovakia) from our local Crate & Barrel. It seems to respond really well to 454.72 Hz, with the lip moving at a pretty good amplitude...maybe it's hitting the speaker enclosure? Anyway, take off your headphones and enjoy watching the oscillations under the strobe light!For more details on our setup see:http://sciencedemonstrations.fas.harvard.edu/presentations/shattering-wineglass
