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  • A Festive Time: Happy Isaac Newton's Birthday

     Apple tree in England by W. Carter, public domain

    Alas, Isaac Newton did not actually suddenly understand gravity due to an apple falling on his head. He might have eaten lot of them, though, as he was stuck at home avoiding a pandemic while he was studying it. Sound familiar, anyone? 

    But, nonetheless, this week is his birthday! So we're sharing a fun resource about Newton's Second Law of Motion, which to give you something to play with at home this week while there's not much else going on... and while you're waiting for classes to start up again so you can see some of our demonstrations of Newton's 2nd!

    The PhET Collection at the University of Colorado has a delightful simulation of Newton's second law in action: Forces and Motion.  There are four different simulations within this one site.

    The first, Net Force, is shown in the image below. A wagon (which appears to be loaded with candy, potentially a sticky situation) has ropes coming off either end. You can drag pulling humanoids onto the rope on either side; the different sizes are scaled to represent the different force they can apply. Try combining different forces, then press “Go” and watch the wagon start moving. You can add and remove figures from the task to change the force beforehand and while it’s in motion, to see how changing the force changes the acceleration.

    3 examples from PhET Forces & Motion

    The second simulation, Motion, has a skateboard on a level plane; you can load people or objects (a box, a trash can, a refrigerator) onto the skateboard and give it a push; see how changing the force or the mass changes the motion.

    The third, Friction, gives us pretty much the same setup – but without the skateboard! See how the force of friction slows the motion compared to moving on the skateboard.

    And finally, Acceleration adds a very simple accelerometer to the setup: a bucket of water! See how the angle of the water’s surface changes as different forces are applied. Fortunately, the bucket doesn’t appear to be able to fall off and get everyone wet, always a good thing on a chilly day.

     See you in January!

  • Demonstration Highlight: The Force on a Current in a Magnetic Field

    Welcome back! This week we’re taking a look at demonstration K1-03, which shows the effect of the force that acts on an electrical current in a magnetic field.

    A wire is suspended between the poles of a large horseshoe magnet.

    A stiffened wire is suspended between the poles of a strong magnet. When we turn on a current through the wire, the wire leaps outwards. If we swap which end of the wire connects to which end of the battery, the direction the wire moves is reversed. What just happened?

    The force in play here is known as the Lorentz Force, named for Dutch physicist Hendrik Lorentz, who formalized the equations for this force based on earlier work by James Clerk Maxwell, Oliver Heaviside, and many other scientists. Today Lorentz is most popularly associated with his later work on relativity, supporting the work of Albert Einstein; but this work partly grew out of his early studies of how charged particles interact with electric and magnetic forces.

    Lorentz’s equation states (in part) that if an electrically charged particle is moving through a magnetic field, that particle experiences a force proportional to its velocity and to the strength of the magnetic field, but perpendicular to both. So as the electrons flow through the wire, passing through the field of the horseshoe magnet, the resulting force will push the electrons (and thus the wire carrying them) sideways, out from between the poles. If we change the direction of the electrons’ velocity, by swapping the direction of the current, then the direction of the force is reversed; the same happens if we reverse the direction of the magnetic field, by flipping over the magnet.

    You can see this in action in an animated simulation from the National High Magnetic Field Laboratory, here: https://nationalmaglab.org/education/magnet-academy/watch-play/interactive/lorentz-force

    Click on the switch graphic to complete the circuit, and you can see the motion of the wire. Buttons will let you change the direction of the magnetic field and the current; try one, then the other, then both, and see if what happens matches what you expect!

     

     

     

     

  • Demonstration Highlight: Tyndall's Experiment

    Today we’re featuring an interesting experiment that explores the classic question of springtime: Why Is The Sky Blue?

     Demonstration M7-31: Tyndall’s Experiment uses a chemical reaction to simulate light scattering through Earth’s atmosphere, but in a tiny container. Solutions of sodium thiosulfate and hydrogen chloride are dissolved in water, then mixed together in a glass tank in front of a light source. These chemicals react and form new particles. The resulting particles form a colloid, a liquid with particles suspended throughout, giving it optical properties that let it simulate our much thinner atmosphere on a smaller scale. Over the course of several minutes, as more and more particles form, we see more and more light scattered out the sides of the tank, while less and less passes straight through. As it goes through this transition, the light coming out the end changes from nearly white, to orange, to red, perhaps finally vanishing entirely.

     Demo M7-31: a light source and a glass tank for chemical mixing

     In the atmosphere, light scatters off of molecules and other tiny particles in the air. The angle at which light scatters depends on the wavelength of the light; shorter wavelengths scatter farther than longer ones. Visible light consists of a spectrum of various wavelengths, with blue light having shorter wavelengths and red light having longer wavelengths. This means that blue light scatters more than red.

    Linear visible spectrum, with wavelengths in nanometers - public domain image from David Eccles of Victoria University of Wellington https://commons.wikimedia.org/wiki/File:Linear_visible_spectrum.svg

    This property in the atmosphere was written about by physicists John William Strutt, Lord Rayleigh, and is commonly called Rayleigh Scattering as a result; but the experiment to observe similar effects in a liquid was developed by physicist John Tyndall, hence the name of the demonstration. John Tyndall was well known in his time for his interest in education, and gave public lectures with demonstrations, much like we do today! He also carried out important research on the effect of carbon dioxide in the atmosphere, what we now know as the greenhouse effect.

     Rayleigh scattering in the atmosphere: public domain image credited to Rnbc https://commons.wikimedia.org/wiki/File:SDIM0241b.jpg

    As the Earth turns, the angle we see the sun at changes. Early and late in the day, we’re seeing the sun through the atmosphere at a different angle, and looking through more atmosphere as a result. So at those times we mainly see red light; the shorter blue wavelengths have been scattered away. At midday, with the sun shining directly down on us, we see more blue!

     A fascinating bit of physics, and also very beautiful.

     

  • Falling into Free Fall

    A few articles we ran across this week, two new and one old, have had us thinking about that ever-popular topic for the first week of the semester: Galileo, and the forces acting on objects in free fall.

     One of the basic concepts students struggle with in the early stages of introductory kinematics is the concept of free fall, and how different objects behave when falling. This question takes us back to the classic experiment Galileo may or may not have actually carried out, dropping objects of different masses from the top of a tower and observing that, barring drag, they fall in unison, regardless of their respective masses. Here at the Lecture-Demonstration Facility, we have a variety of demonstrations to help illustrate this concept, many of them quite popular in introductory classes... both because they are helpful illustrations of this important physics concept, and because falling objects make a satisfying bang. If you are teaching this topic here soon, be sure to explore sections C2 and C4 of the demonstrations index to see what we have to offer.

    Leaning tower of Pisa; Galileo probably did not actually drop things from here. image courtesy cyark.org

    This was brought to mind recently when we came across an article from 2013 about efforts to rescue the endangered Leaning Tower of Pisa. Despite the legend, Galileo probably did not actually drop balls from the top of this tower; it does, however, make an excellent illustration for discussing the problem, and is popular in many textbooks for this reason regardless of historical relevance. The effort to save the tower from finally falling over entirely does itself lead to some interesting physics questions, discussed in the article, and could be interesting to students as an opportunity to talk about issues of force and torque, equilibrium and the center of mass. To explore other aspects of this problem in class, check out demonstrations B1-02 and B1-03.

    In a recent paper in the European Journal of Physics Education, Balukovic & Slisko explore some of the potential causes of student confusion around weightlessness in free fall, and ways to address them. They recommend using multiple demonstrations and problem solving to help students engage in active learning around the topic. They also have suggestions on thinking about how we use language itself to talk about physical problems to improve clarity and understanding.

    Leaving the Renaissance largely behind, this classic image of Galileo dropping his spheres is cited again in an article posted last week in Physics Today. Discussing recent research by Hebestreit, Novotny, et al., they report on the latest experiments in using optically-trapped nanoparticles as tiny force meters. When the optical trap is turned off, the nanoparticle “falls” or responds to other outside forces. By rapidly turning the trap off and on, they can measure the acceleration of the briefly free-falling particle to a high degree of precision, and can thus potentiallly use it as a measurement tool.

    News items like this can be very useful in class to promote student engagement. Helping students see how the basic concepts we're teaching can be tied in to both cutting-edge research and real-world problems helps them both understand the concepts and better value what they learn.

     

    Balukovic, J., & Slisko, J. (2018). Teaching and Learning the Concept of Weightlessness: An Additional Look at Physics Textbooks. European Journal of Physics Education9(1), 1-14. DOI: https://doi.org/10.20308/ejpe.v9i1.168

    Hebestreit, E., Frimmer, M., Reimann, R., & Novotny, L. (2018). Sensing Static Forces with Free-Falling Nanoparticles. Physical Review Letters121(6), 063602. DOI: 10.1103/PhysRevLett.121.063602

    Miller, J. (2018) Free-falling nanoparticles help to detect tiny forces. Physics Today.DOI:10.1063/PT.6.1.20180823a

    Watt, S. (2013). Propping up the wall: How to rescue a leaning tower. Science in School, 26. 

     

  • Happy 100th Birthday Katherine Johnson!

    Today marks the 100th birthday of NASA scientist Katherine Coleman Johnson. For decades, she was one of the leading minds of NASA’s space navigation program, plotting courses of the Mercury, Apollo, and Shuttle programs, including both the 1969 Apollo 11 moon landing and the 1970 recovery course of the aborted Apollo 13.

     Katherine Johnson at NASA in 1966; image credit NASA

    Born in rural West Virginia in 1918, a career in mathematics and physics was not an easy course for a young African-American woman. She faced massive discrimination on all sides, but demanded her place in the technical community. She joined the staff of the National Advisory Committee for Aeronautics (NACA) in 1953 as a computer, and stayed on through multiple technical posts as the organization became NASA, the National Aeronautics and Space Administration. in 1958.She contributed to many of the major space missions of the time, and had a reputation as the most best mathenatician on the team. For his 1962 solo orbital mission, then-astronaut (and later Senator) John Glenn refused to go into orbit without Johnson plotting his navigation before he stepped aboard.

    Katherine Johnson at NASA Langley Research Center in 1980; image credit NASA

    A partial bibliography of her technical publications can be found on her NASA History page at https://crgis.ndc.nasa.gov/historic/Katherine_Johnson . Johnson retired from NASA in 1986, but resides in Hampton, Virginia near Langley Research Center to this day.

     Katherine Johnson in 2016 at the Hidden Figures film premiere; image credit NASA

    In recent years, Johnson and her compatriots have begun to receive greater recognition for their work. The 2016 book and film Hidden Figures helped to bring public attention to the computational work behind many famous space missions. A new research center at NASA Langley was named for Johnson [https://www.nasa.gov/image-feature/langley/nasa-celebrates-katherine-johnson-with-building-named-in-her-honor], and last week West Virginia University unveiled a statue of her and launched a scholarship fund in her name in recognition of her studies in the state and her struggle against segregation and sexism. [https://www.wvgazettemail.com/news/katherine-johnson-immortalized-with-statue-on-wv-state-university-campus/article_faaaff7b-e452-5de5-8612-892a64a514bd.html]

     As we begin the new school year, this is an excellent opportunity to think about how we can teach our students more about the history and diversity of our field, and the different paths we can all take in our careers.

    Links:

    NASA celebration of Katherine Johnson’s 100th birthday, and resources for educators:

    https://www.youtube.com/watch?v=_ERy7-Pd0dU

    https://www.nasa.gov/audience/foreducators/a-lifetime-of-stem.html

    Official NASA biography of Katherine Johnson, by Margot Lee Shetterly: https://www.nasa.gov/content/katherine-johnson-biography

    The Newport News Daily Press on Johnson’s 100th birthday: http://www.dailypress.com/news/science/100708055-132.html

    Beyond Curie, resources for educating about women in science: Katherine Johnson https://www.beyondcurie.com/katherine-johnson/

    Mental Floss: 9 Fascinating Facts about Katherine Johnson http://mentalfloss.com/article/555114/facts-about-katherine-johnson-nasa

     

     

  • Happy Birthday Carl Sagan

    This week marks the birthday of the late scientist and science educator Carl Sagan, born in 1934. Sagan is best remembered today for his work popularizing and communicating science, particularly with his several books and his popular television program Cosmos.

    Carl Sagan stands beside a model of the Viking Mars lander (NASA photo)

    Less well known these days, however, is his professional work as an astrophysicist studying planetary atmospheres. He contributed to early work establishing surface conditions on Venus, extrapolating pressure and temperature ranges from radar reflectivity data. He likewise studied atmospheric flow on Earth, Mars, Jupiter, and the trace gases of the Galilean moons.

    In conjunction with his science education work, he went on to extrapolate from this and argued convincingly of the potential perils of climate change on Earth as well, as reflected in the more extreme changes on Venus.

    But in the end, his most crucial contribution was as an educator and communicator of science, bringing his joy and fascination with scientific discovery to the masses, and inspiring many young people to follow his path into the sciences.

      

     Some of Sagan's early work:

    Sagan, C. (1961). The planet Venus. Science, 133(3456), 849-858.

    Sagan, C. (1962). Structure of the lower atmosphere of Venus. Icarus, 1(1-6), 151-169.

    Sagan, C., & Pollack, J. B. (1967). Anisotropic nonconservative scattering and the clouds of Venus. Journal of Geophysical Research, 72(2), 469-477.

    Sagan, C., & Veverka, J. (1971). The microwave spectrum of Mars: An analysis. Icarus, 14(2), 222-234.

    Sagan, C., & Mullen, G. (1972). The Jupiter greenhouse. Icarus, 16(2), 397-400.

    Sagan, C., & Mullen, G. (1972). Earth and Mars: Evolution of atmospheres and surface temperatures. Science, 177(4043), 52-56.

    Sagan, C., Toon, O. B., & Gierasch, P. J. (1973). Climatic change on Mars. Science, 181(4104), 1045-1049.

    Sagan, C. (1975). Windblown dust on Venus. Journal of the Atmospheric Sciences, 32(6), 1079-1083.

    Sagan, C., & Bagnold, R. A. (1975). Fluid transport on Earth and aeolian transport on Mars. Icarus, 26(2), 209-218.

    Smith, B. A., Soderblom, L. A., Johnson, T. V., Ingersoll, A. P., Collins, S. A., Shoemaker, E. M.,... & Cook, A. F. (1979). The Jupiter system through the eyes of Voyager 1. Science, 204(4396), 951-972.

    SMITH, B. A., Soderblom, L. A., Beebe, R., Boyce, J., Briggs, G., Carr, M.,... & Hunt, G. E. (1979). The Galilean satellites and Jupiter: Voyager 2 imaging science results. Science, 206(4421), 927-950.

    Squyres, S. W., Buratti, B., Veverka, J., & Sagan, C. (1984). Voyager photometry of Iapetus. Icarus, 59(3), 426-435.

    Sagan, Carl, et al. "Polycyclic aromatic hydrocarbons in the atmospheres of Titan and Jupiter." The Astrophysical Journal 414 (1993): 399-405.

     

    https://en.wikipedia.org/wiki/Carl_Sagan

  • Happy Birthday to Émilie du Châtelet

    This week marks the birthday of Émilie du Châtelet, French philosopher and scientist best remembered today for first developing the concepts of kinetic energy and the conservation of energy in physical systems.

     Portrait by Latour of Gabrielle Emilie Le Tonnelier de Breteuil, Marquise du Châtelet

    Born Gabrielle Émilie Le Tonnelier de Breteuil in Paris in 1706, Émilie was the daughter of prominent couriters. She had an early talent for both languages and mathematics, and was fortunate to have parents who could provide her with tutors in a time when such topics were rarely available to women. At the age of 19 she married the older Marquis du Châtelet; his work kept him away on his travels, and she devoted much of her time to mathematics, philosophy, and the arts.

     

    Émilie du Châtelet’s training in languages enabled to read Isaac Newton’s recently published Principia Mathematica, and she translated it into French (her translation remains the standard French version of the text to this day). In her studies and experiments on falling masses, she extended Newton’s concept of momentum to postulate a separate quantity that was not proportional to velocity, like momentum, but the square of the velocity – which we now know as kinetic energy. From this eventually developed the implication that energy is a constant quantity in a system that could be conserved, though the full mathematical understanding of this had to wait another two hundred years for the work of German mathematician Emmy Noether.

     Cover of Chatelet's Dissertation sur la nature du feu

    She also studied the physics and chemsitry of compusion, in part in collaboration with the philosopher (and her occasional partner) Voltaire, and published an essay on the topic in 1744.

    Émilie du Châtelet was also famous in her day not only as a philosopher and scholar, but as a socialite and patron of the arts, fond of carousing, gambling, and drama. Perhaps some of her spirit lives on in our students today.

  • Happy birthday, Alexander Müller

    Today marks the birthday of Swiss physicist K. Alexander Müller, who shared the 1987 Nobel Prize in Physics with Georg Bednorz for their discovery of the first high temperature superconductor.

     Born on April 20th, 1927 in Basel, Switzerland, Alex Müller attended the Eidgenössische Technische Hochschule Zürich, the Federal Institute of Technology at Zurich, where he received his PhD in 1957. He worked at a variety of institutions throughout Switzerland, studying various aspects of what we now term Condensed Matter Physics.

     In the 1980s, Müller and Bednorz were working together searching for high temperature superconductors. “High temperature,” in the context of superconductors, can be misleading to newcomers, as they are still very cold!

     Superconductors are materials whose resistance drops to zero at low temperatures. These materials have many fascinating properties – they can transmit electricity with no loss, and they repel all magnetic flux. Generally, a superconductor has a criticaltemperature below which it exhibits superconducting properties; above this temperature it does not, behaving as ordinary materials do. For many superconducting materials, and all of those discovered in the first seventy years of them being studied, this temperature is around ten to twenty Kelvin, a temperature very difficult to achieve, maintain, or work with.

     Müller and Bednorz, however, in 1986 discovered a ceramic compound material, lanthanum barium copper oxide, with a critical temperature of 35 Kelvin. Still very cold, but a definite improvement! More crucially, in addition to showing that higher critical temperatures were possible, they showed that superconductivity could be achieved in ceramics, driving other researchers to investigate similar compounds for this effect. Within a year, other such materials had been discovered, including the now popular yttrium barium copper oxide by Paul Chu of the University of Houston. This new material had a critical temperature of 92 Kelvin!

     92 Kelvin is still almost -300 degrees Fahrenheit below zero, obviously much colder than any temperature found naturally on Earth! But it is much warmer than the early metal superconductors. And crucially, it crosses an important line: 77 Kelvin is the temperature of liquid nitrogen, a refrigerant that is much cheaper and easier to manufacture than the liquid helium used in earlier studies, and vastly easier to work with. Since these newest materials can exhibit superconducting behaviour at liquid nitrogen temperatures, it means we can use them in practical technology and experiment with them more easily… including in classroom demonstrations!

     placing a magnet on a superconducting disc

    We currently have two demonstrations that use high temperature superconductors, both taking advantage of their effect of excluding magnetic flux. Demonstration I7-21: Superconductor – Magnet Levitation uses a yttrium barium copper oxide (YBCO) disc bathed in a liquid nitrogen bath. When a small permanent magnet is placed on top of the disc, the strong magnetic field is repelled from the superconductor, so strongly that the magnet itself levitates above the disc!

     large magnetic track

    Taking the opposite approach, demonstration I7-23: Magnetic Track and Superconductor, built by our own Don Lynch, consists of an array of powerful neodymium magnets. A puck of high temperature superconducting material wrapped in a Teflon sheath is soaked ahead of time in liquid nitrogen, cooling it down such that it will hold its temperature for a few minutes. The puck is cooled while resting above a small block of magnets. When taken out of its bath and placed on the track, it again holds itself at the same height above the magnets of the track.

     

    Resources:

    The Nobel Prize in Physics 1987 at nobelprize.org

    J. G. Bednorz and K. A. Müller (1986). "Possible highTc superconductivity in the Ba−La−Cu−O system". Z. Phys. B64 (1): 189–193.

     

  • Hot Air Balloon

    One of the most popular and visually stunning illustrations of buoyancy and relationship between temperature and pressure is the hot air balloon. Some of you may have had a chance to see one recently at our Maryland STEM Festival event, FLIGHT!

     A hot air balloon rises in the air as a result of its buoyancy. As the air is heated, the increased average kinetic energy of the particles in the gas mean its average density is less, and so it rises through the air. In the outdoors, a modern hot air balloon carries its heat source with it, and can keep the air at a constant higher temperature, so the balloon will rise until it reaches equilibrium at an elevation where the density of the outer atmosphere is no longer sufficiently higher than that of the air in the balloon.

    Hot air balloon particles, density varies with temperature, illustration by kayau

     Our demonstration balloon, however, more closely resembles the earliest experimental crewed hot air balloons, which heated the air with a heat source located on the ground (a bonfire then, an electric heat gun for us). So these balloons rise only until they have gone too far from the fixed heat source and the air begins to cool down again, reducing buoyancy until they settle back to the ground – or return to the heat source!

    A red and yellow plastic hot air balloon floats near the ceiling of a UMD Physics lecture hall, early 2000s

     The earliest records of the development of uncrewed hot air balloons, like ours, go back over 1,000 years in China, and are recorded some other parts of East and Southeast Asia as well. The were used for entertainment purposes and for signaling between distant points. The earliest known crewed hot air balloon experiments currently known date to the eighteenth century in Europe, though others may have occurred earlier elsewhere.

    Coloured etching of Montgolfiere balloon experiment, 1783. A large and ornate hot air balloon is tethered to poles as it prepares to launch above a bonfire.

     Simple hot air balloons are easy to make, and are a fun home experiment. Larger demonstration models can be valuable in class to spur discussion of buoyancy and the behaviour of gases, and studying the history of both the technology and the theoretical understanding of their thermodyanmics can be a useful and interesting student project.

     

     

  • Irene Joliot-Curie

     Irène Joliot Curie (1897 1956), c. 1935 (credit: Smithsonian Institution Archives http://siarchives.si.edu/ )

    This week marks the 121st birthday of Irène Joliot-Curie , born 12 September 1897. Most widely remembered as the daughter of Marie and Pierre Curie, she was an important scientist in her own right, and shared a Nobel Prize with her partner Frédéric Joliot-Curie in 1935.

    Born while her parents were working in Paris, Irene grew up in the scientific community. For part of her childhood her family, along with other local academics like the Langevins and Perrins, created a cooperative homeschooling program that introduced the children to principles of science, mathematics, languages, and art at a more advanced level and more diverse forms than was offered in the local schools at the time. They encouraged learning through play and self-expression in ways that were innovative in early education in Europe. She later went on to attend the Collège Sévigné in Paris before enrolling at the Sorbonne.

    Irene's collaboration with Frédéric Joliot began with her as his tutor in laboratory techniques, then became a full partnership. Some of their early scattering experiments with alpha particles from polonium (discovered by Marie & Pierre Curie when Irene was a child) provided the first data that led to the discovery of the neutron, though the Joliot-Curies themselves initially attributed these results to exceptionally high-energy gamma radiation rather than hypothesizing a new particle. Sometimes it turns out the least simple explanation is the correct one!

    Their most important and memorable work came a few years later, though, in the 1930s as they studied the irradiation and decay of nuclei and discovered that, under proper conditions, one element could be transmuted or broken down into others, something previously thought impossible since the time of Democritus. It was this work that won them the Nobel Prize.

    Irene Joliot-Curie was active in politics as well. Throughout the 1930s, she and her partner were active in the anti-fascist movement in France, concerned about the rise of totalitarianism in Germany and Spain.Joliot-Curie also accepted a government appointment as Undersecretary of State for Scientific Research, and was instrumental in founding CNRS, the French national science agency. Long a proponent of public access to scientific data, she temporarily changed this position late in the 1930s, locking away all of their research on nuclear fission in the vaults of the French Academy until after the Second World War. Afterwards, however, she returned to scientific publishing. She was also a proponent inclusivity in science and science education.

     Irene & Frederic with student Qian Sanqiang in 1948

    Accidental exposure to radioactive materials in the laboratory led to Irene Joliot-Curie's early death in 1956. For obvious reasons, large containers of polonium are not recommended as classroom demonstrations. But this is an excellent opportunity to introduce the concept or radiation and particle scattering, with samples of weakly radioactive materials and a Geiger counter. Joliot-Curie's life also helps illustrate the importance of science education and the inextricable ties between scientific research and world affairs.

     Frederic and Irene Joliot Curie circa 1940s

     

    References and Further Reading:

    Nobel Foundation

    Royal Society for Chemistry

    Charles Sowerwine (2018), France Since 1870, Macmillan.

    Wikipedia

    Woodrow Wilson National Fellowship Foundation

     

     

  • Seeing Sound: Vibrations on a Plate

    This week, a tweet by Simone Schnall of Cambridge University went viral on Twitter, sharing a video by British science presenter Steve Mould

    Coincidentally, this week also marks the birthday of Ernst Chladni, for whom this phenomenon is named- Chladni Figures. 

    sand forms patterns on a square steel plate as it is stroked by a violin bow

    Sand is sprinkled on top of a plate. As it vibrates, the sand traces out the pattern of node and antinodes, accumulating along the lines where the plate is at rest, and being driven away from the areas where the plate is moving up and down with the sound wave. In its simplest form, the plate would be clamped at the center and driven by the bow at one edge; as you change the bow position, you can excite different vibrational modes of the plates and form different patterns. But pressure elsewhere on the plate, even something as simple as pressing your thumb against the edge, can form a node and thus change the pattern of standing waves.

    Of course, this can be made far more complex, and the formation of these patterns can be used to staudy how different objects vibrate in different conditions. This is still used today to help in the design of musical instruments.

    If you are teaching this topic at UMD, consider using our own set of Chladni plates, and invite your students to try it for themselves. Or, for greater complexity (and volume), try the oscillator driven version. By using an audio oscillator to drive the plate from the center, a wide range of modes can be observed by carefully varying the driving frequency. For this version, we can also offer a wider variety of plate shapes, including a model of a violin back. 

    g4 22hg4 22i

    To learn more about Ernst Chladni, Chladni Plates, and the history of acoustics, visit these pages at the Smithsonian and at Cambridge's Whipple Museum.

     

  • Space News: The Nancy Grace Roman Space Telescope

    NASA announced last month that their upcoming infrared observatory project had been named the Nancy Grace Roman Space Telescope. Today, we’re going to take a brief look at this project, Dr. Roman, and the role of physics in astronomy.

     NR-WFIRST spacecraft modelNR-WFIRST primary mirror assembly

    Nancy Grace Roman (1925-2018) was the first Chief of Astronomy for NASA, and the first woman ever to hold an executive-level position there. A graduate of Western High School in Baltimore, and later of Swarthmore College and the University of Chicago, she began her career in astronomy research specializing in the emission spectra of stars.

     spectrum of Oxygen - image credit McZusatz

    Spectroscopy is the study of the spectrum of light, the individual frequencies and colors that make up the light we see. Every element and compound emits its own distinctive pattern of frequencies of light, based on the structure and energy of the electrons within the atom. By analyzing the light from stars, we can use these distinctive patterns as a kind of fingerprint to identify the chemical makeup of distant stars and planets. Our demonstration collection at UMD Physics has many demonstrations about spectra and spectroscopy; be sure to click here and check them out!

     Not all light is visible to our eyes; lower frequency light is below the range that we can see, in infrared wavelengths. Space telescopes are often valuable for observing this invisible light without interference from our atmosphere, just as they are in the visible spectrum.

     Dr. Nancy Roman with an early satellite model

    Despite her skill as a researcher, the widespread discrimination against women in the sciences made it difficult for Dr. Roman to advance her career in academia. Eventually, she moved to working in government instead, first joining the Naval Research Laboatory and then NASA. She essentially created the astronomical science program at NASA, plotting its course for decades to come. She was a key player in the development of many of NASA’s research satellites, including Uhuru, the first X-ray astronomy satellite; and she was a leader in the creation of the Hubble Space Telescope. She advocated that NASA science should be for everyone, and ensured that their research and data were publicly available.

     Nancy Grace Roman in 2015

    Dr. Roman retired from NASA, and began a second career in scientific computing. She learned programming at Montgomery College and went on to work as a contractor specializing in scientific data management, eventually returning to NASA as a contractor to manage the Astronomical Data Center at Goddard Space Flight Center.

     Dr. Roman worked hard to inspire more women to become scientists and leaders in science, and we can hope to follow in her footsteps.

  • STEM News Tip: AIP Celebrates 90th Anniversary This Month

    The American Institute of Physics is a federation of physics-related scholarly societies with the goal of advancing and promoting the physical sciences. AIP was first founded in 1931 in New York, but has since moved much of its operations to College Park for proximity to both other locally based member societies and the federal government in Washington DC.

    To celebrate the 90th anniversary, AIP is hosting a free virtual event and Trivia Night on July 22. You can learn more and sign up for the event at https://www.aip.org/aip-90th-trivia-night . Space is limited, so sign up soon!

  • STEM News Tip: AIP Oral History Interviews

    One of the many programs within the American institute of Physics, based right here in College Park, is the Niels Bohr Library and Archives. This program serves as a center for physics history, a repository for documents and images and other records of physics over the decades.

     One of their current projects is expanding their collection of oral history recordings. These interviews, carried out over the past 60 years, serve as records both of great scientific discoveries of the era and of many physicists’ personal experiences within the worlds of academia, industry, and government. Their collection can be browsed online, and is a fascinating way to explore the history of our field.

     A new interview with UMD’s own Prof. Joe Redish was recently added to the collection, you can read the transcript here as he discusses his experiences first as a nuclear theorist and his transition to education research.

     But Prof. Redish isn’t the only UMD physicist with an interview in the collection. Other past and present faculty who have been interviewed include Joseph Weber, Bob Park, and Carroll Alley. You can also read interviews with prominent UMD Physics alumni, like Dr. Han Wen of the National Institutes of Health, Goetz Oertel of the Department of Energy, and Robert Herman of JHU’s Applied Physics Lab.

     Click here to check out all the UMD folks in the archive!

    Or explore the full oral history collection at AIP: https://www.aip.org/history-programs/niels-bohr-library/oral-histories

  • STEM News Tip: Native American Physics & Astronomy

    Recognizing and including diverse viewpoints in an important part of the scientific endeavour, albeit one often neglected. Fortunately, inclusion is coming to be more widely seen as an important part of physics and physics education. Today we're looking at one particular community, Native Americans/First Nations in 

    Canada's The Walrus magazine had a recent feature article on First Nations astronomy - both on the traditions of the study of the stars in their history, and on First Nations people and understandings in academia today. There is increasing support for bringing multiple approaches to understanding into the classroom; read more about it here. Also, check out the upcoming Indigenous Star Knowledge Symposia.

    Several organizations are working to expand the role of Native peoples in the sciences; visit their sites to learn more

  • Today in Physics History: Neptune

    This week marks the anniversary of the official discovery of the planet Neptune. 

     Neptune seen by Voyager 2, public domain image by NASA

     [image of Neptune taken by Voyager probe, NASA]

    Neptune’s existence had predicted mathematically before it was observed; but it was finally seen via telescope, at last, on Sept 23-24 1846 by Johann Galle and Heinrich d’Arrest, making it the first planet to be predicted via the laws of physics before it could be identified in the sky.

    Earlier measurements of the orbit of Uranus had detected some irregularities in its orbit. By extrapolating from Kepler’s and Newton’s laws about gravitation and motion, it could be established that some additional mass was generating a force on Uranus; one possibility was that this was another, more distant planet. Two different scientists, Urbain Le Verrier and John Couch Adams, both calculated the existence of this planet and made predictions about its position in the sky.

     Using Le Verrier’s calculations, Galle and his assistant d’Arrest were able to locate an object in the sky via the telescope of the Berliner Sternwarte, the Berlin Observatory, in the position predicted by Le Verrier. Tracking it, they established that it was indeed a planet following the predicted orbit. For the first time, rather than just logging observations and building predictions based on them, scientists had succeeded in predicting a planet mathematically and then locating it where theory predicted it to be.

     This is part of how theory helps us understand what we see, as well as predicting where to look. In retrospect, it was discovered that Neptune had been sighted before, bu Galileo, Herschel, and others – but nobody ever determined for certain that what they were seeing was a planet. Other observers, working both from Adams’ calculations and Le Verrier’s, were searching for the planet as well, but did not find it – or found it but did not realize they had!

     This is the essence of the physical sciences – we use mathematical tools to make predictions about the world, and use experiments and observations to confirm or disprove those predictions, and to understand what we observe. We carefully organize our data, and report on our work to our collaborators and peers. Then we use what we learned to refine our theories, making better tools for further experiments and predictions. All of physics builds on these basic principles, whether you’re making a prediction in a first-year physics class about the motion of a ball on a track, or calculating where to point a telescope to discover a new part of the universe, we are all doing science.

     handwritten journal entry by Galileo Galilei with notes about an object seen in the sky

     [a page from Galileo's notes, with a possible observation of the planet Neptune, never confirmed]

    Read more about Neptune and its discovery

     

  • Women Nobel Laureates in Physics

    Earlier this month, Prof. Donna Strickland, along with two other physicists, won the Nobel Prize in Physics for her work with lasers. She is the third woman to win the Nobel Prize in Physics in over 100 years of it being awarded. (Irene Joliot-Curie won the Nobel Prize in Chemistry, though she was primarily a physicist by profession by our modern standards.) Let's take this opportunity to look back at these three women (and hope that this list gets longer soon!)

     Nobel Prize Medal - image public domain in US

    Marie Skłodowska Curie is perhaps the best known woman in the history of physics. She shared the Nobel Prize in Physics in 1903 with Pierre Curie and Henri Becquerel for their research on radiation. She later went on to win the Nobel Prize in Chemistry in 1911, for her work on radium and polonium.

     

    Maria Goeppert-Mayer won the Nobel Prize in Physics in 1963 for her development of the nuclear shell model, sharing the prize with Eugene Wigner and Hans Jensen. Her work provided the first clear explanation for the stability or instability of different atomic nuclei, by showing that the nucleus could be modeled as a series of shells of nucleons with coupled spins. She is the only woman to win the prize for theoretical rather than experimental work.

     

    This year, 2018, Donna Strickland won the Nobel Prize in Physics for her development of chirped pulse amplification in lasers. This is the method used in most modern high-powered laser research installations to increase the energy available in ultrashort bursts.

     

    This is an appallingly short list for over a century of work, and provides an excellent opportunity to talk with our classes about the history of physics and about the challenges and discrimination women still face in our field. Consider: What can we as scientists and educators do to make our field more welcoming and inclusive?

     

     

    Some resources:

    UMD Women in Physics https://www.physics.umd.edu/wip/

    APS Women in Physics https://www.aps.org/programs/women/

    The Nobel Prize in Physics in 1903 https://www.nobelprize.org/prizes/physics/1903/summary/

    The Nobel Prize in Physics in 1963 https://www.nobelprize.org/prizes/physics/1963/summary/

    The Nobel Prize in Physics in 2018 https://www.nobelprize.org/prizes/physics/2018/summary/

    Nature: Donna Strickland on her work and on the under-representation of women in physics https://www.nature.com/articles/d41586-018-06995-w

    Particles for Justice https://www.particlesforjustice.org/