Today, in exploring the effects of centrifugal force, we see no fewer than seven gadgets demonstrated. Our curator does a lot of cranking. 1. As a spinning glass globe rotates faster, colored liquid within it rises to form a belt or ring around its middle. 2. An array of pendulums starts out hanging vertically, but the pendulums spread out as rotation speeds up. 3. A spring-loaded sphere, arranged to slide on a horizontal bar, moves outward as the bar spins, compressing the spring. 4. Two flexible strips of metal form two circular hoops, outlining an imaginary sphere. As they are spun, they are centrifugally deformed. We see that the shape they outline becomes less like a sphere and more like a pumpkin. This demonstration makes a point of interest to planetary scientists: Many planets—Earth and Jupiter are good examples—bulge slightly at their equators, and are flattened at their poles, because of their rotation. The effect is more subtle than the … Continue reading →
About Bill Higgins
William S. Higgins is a radiation safety physicist at Fermilab involved with the transport of high-energy particle beams. He frequently writes and speaks about spaceflight, astronomy, and the history of science. A graduate of Notre Dame, he lives in Aurora, Illinois.
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Bringing out the wheel-shaped Wimshurst machine once again, today’s electrostatic demonstration involves a spark discharge into a slab of resin. The resin is an insulator, which means that charge does not easily move through it. An excess of charge carriers (which we know today as electrons) cannot quickly disperse; they are trapped in the resin, and a lingering electric field is present along the path of the spark. Similarly, if the spark discharge creates a dearth of charge carriers, electrons elsewhere in the resin cannot rush in to fill the resulting void. Once again, a lingering electric field is present. Last month, I was quoting the 18th-century electrical scientist Georg Christoph Lichtenberg. It was he who first employed fine powders to make visible the track left by a spark in an insulating material. Particles of the powder, attracted by the electric field, accumulate on the surface of the resin. The intricate and beautiful patterns, left in the wake of the … Continue reading →
Today’s video from the Cabinet of Physics illustrates the malleable nature of light. A bright white light illuminates a screen. The curator’s gloved hand inserts a prism into the white beam. On the screen, the former white spot becomes a wide bar of many colors—a spectrum. An array of seven small mirrors intercepts the spectrum. Each mirror reflects an intensely-colored spot onto another screen. The mirrors may be adjusted to make their spots overlap, producing new colors. Finally, when all seven different colors overlap, a new spot of white is created. This simple apparatus taught students how different wavelengths of light could be extracted or recombined to manipulate colors. Computer users observe the same thing every day. If there’s anything white on the screen you’re looking at, it may well be a combination of light from an array of tiny single-color light sources, such as light-emitting diodes or the phosphor dots of a cathode-ray tube. (Or not, depending on the … Continue reading →
Today the curators bring us three devices from the shelves of the Cabinet of Physics. All are induction coils, sometimes called “spark coils.” Each is a transformer. Each takes a low voltage, with input interrupted in on-and-off-and-on-and-off fashion, and converts it to a much higher voltage, high enough to produce a series of substantial sparks across an air gap. Induction coils become supporting players in a number of other videos from the Cabinet. The pulsed high voltage produced by these induction coils is a useful tool for investigating complex electrodynamic and electromagnetic phenomena that featured prominently in late 19th-century physics. One example is the colorful Geissler discharge tube we see as the third coil, the mighty Ruhmkorff coil, is demonstrated. The high-voltage pulses pass through low-pressure gas sealed within the glass tube. The Foundation for Science and Technics, or Fondazione Scienza e Tecnica, of Florence, Italy, has made available many videos exploring the Cabinet of Physics, a large collection of antique … Continue reading →
The operation of a lightning rod, which is designed to protect a building from lightning strikes, is demonstrated in today’s Cabinet of Physics video. A wooden model house is equipped with a metal rod projecting above its roof. “Lightning” is provided by a group of Leyden jars, those high-voltage capacitors which have been faithful workhorses of electrostatic demonstrations for most of three centuries. The jars are charged by a wheel-like electrostatic generator; I’m not a connoisseur of such devices, but this one resembles a Wimshurst Machine I’ve played with. To add drama to the Thunder House demonstration, a firecracker is connected to its lightning rod. No doubt this flourish made the lesson more memorable–and probably more enjoyable–to students. Enthusiasts of electrostatics love to quote the 18th-Century experimenter Georg Christoph Lichtenberg, who said: “A physical experiment which makes a bang is always worth more than a quiet one. Therefore a man cannot strongly enough ask of Heaven: if it wants to … Continue reading →
The beautiful and intriguing figures of Jules Antoine Lissajous result from juxtaposing oscillating motion along one axis with another oscillation, along another axis, at right angles to the first. As a 20th-century student of physics, I was introduced to Lissajous curves in an electronics lab. One connected two signal generators, each making a voltage varying like a sine wave, to the inputs of an oscilloscope. The relative frequency, phase, and amplitude of the two sine waves gave the green squiggles on the screen their peculiar shape. I learned to play with knobs to vary these signals, and how to make a straight line, a circle, an ellipse, a saddle shape, a three-pointed crown, and other shapes. I could make them dance, revolve, and transform from one exotic shape into another. Oscillations are studied in many different branches of physics; this was a good way to get an intuitive feel for how different oscillatory motions might combine. (Another place to encounter … Continue reading →
Since many of the inventions of the 19th century exploited the interactions between electricity and magnetism, it was important to give students and understanding of these effects. Here are three devices from the Cabinet of Physics that demonstrate eddy currents: the Arago disk, the Foucault apparatus, and the Ruhmkorff electromagnet. Eddy currents are currents that flow through a metal object that moves through a magnetic field. Their effects can interfere with the operation of electromagnetic devices, so engineers learn techniques for minimizing eddy currents–examples here are the second Arago disk, which features radial slots cut into it, and the dangling cube made up of many thin layers of copper as opposed to a solid copper cube. The Foundation for Science and Technics, or Fondazione Scienza e Tecnica, of Florence, Italy, has made available many videos exploring the Cabinet of Physics, a large collection of antique scientific demonstration instruments. The Foundation’s homepage may be found here, and its Youtube channel, florencefst, … Continue reading →
Here is an instrument dear to the hearts of astrophysicists: the spectroscope. We see the steps involved in observing the spectrum of an arc light. The vintage single-prism spectroscope is provided with a scale to measure features of the spectrum; it’s notable that in the gas-lit era when this instrument was used, a separate burner was needed to illuminate the scale… During the 19th century the spectroscope, which allows its user to investigate all the wavelengths shining from a light source, became an essential tool of chemistry. Later, in combination with large telescopes, the spectroscope also proved invaluable to astronomy. In the 20th century, its measurements provided the foundation for unraveling the nature of the atom and the laws of quantum physics. The Foundation for Science and Technics, or Fondazione Scienza e Tecnica, of Florence, Italy, has made available many videos exploring the Cabinet of Physics, a large collection of antique scientific demonstration instruments. The Foundation’s homepage may be found … Continue reading →
In this brief video from the Cabinet of Physics, we see Morin’s Machine demonstrate that uniform horizontal motion, combined with accelerated vertical motion, together trace a path with the form of a parabola. Such motions describe many flying and falling objects, such as a projectile shot from a cannon or catapult. The smooth curve drawn by Morin’s Machine may help a student visualize the connection between falling bodies and the algebra that generates parabolic curves. The Foundation for Science and Technics, or Fondazione Scienza e Tecnica, of Florence, Italy, has made available many videos exploring the Cabinet of Physics, a large collection of antique scientific demonstration instruments. The Foundation’s homepage may be found here, and its Youtube channel, florencefst, here.Continue reading →
The Cabinet of Physics, a fabulous collection of antique scientific devices I essentially stumbled upon (as I related yesterday) in Florence, has a long history. It may also have a bright future. “Cabinet” is an old word, dating from the sixteenth century, for a room holding an array of remarkable objects, such as specimens in a natural history collection. In the 19th century, as Italy grew toward becoming an industrial nation, its need for technically-trained workers also grew. In Tuscany, the region of Italy surrounding the city of Florence, this challenge was met by the Istituto Tecnico Toscano. Mathematician Fillippo Corridi became its first Director in 1853. In his zeal to create an excellent technical school, he worked to provide the Institute with modern laboratories, with a library, and with a large array of mineral and biological specimens. Corridi also began to collect equipment that could be used in teaching the physical sciences to young engineers and technicians. That was … Continue reading →
I found something amazing in Florence. I had no idea it was there, until the moment I found it. Two years ago, I said goodbye to Brother Guy Consolmagno. He’d accompanied me from Rome to Florence, Italy. We’d spent three days together touring the treasures of the legendary city, but now it was time for him to board a train back to Rome and return to the Vatican Observatory. I was left alone with my Firenzecard. A Firenzecard costs 72 Euros and it grants access to over seventy museums around Firenze, that is, Florence. It confers other privileges, such as a very short line at the fabulous Uffizi Gallery (I liked to pretend I was a visiting Medici cousin, getting special treatment), and free WiFi access in certain locations (not even the wealthy Medicis enjoyed WiFi!). A Firenzecard expires 72 hours after it’s purchased. Mine had one day left to run. Florence still had many more museums to offer. What … Continue reading →
When I set out to experience a Pluto flyby, I did not anticipate that I would be getting involved with hats. In the middle of July, I was hanging around the Kossiakoff Conference and Education Center at Johns Hopkins University’s Applied Physics Laboratory, home of the New Horizons project. I was there to assist a team of educators working on public outreach about the mission. Over a thousand visitors were present. In a corner of the center was a table. Artwork of Pluto, its moon Charon, and NASA’s New Horizons spacecraft decorated a large backdrop behind the table. On the table was a professionally-made one-eighth-scale model of the spacecraft. It was a very nice model. But it wasn’t what drew the attention of visitors. What visitors were looking at was the hats. Large hats. In the shape of the New Horizons spacecraft.Continue reading →