The Exploratorium in San Francisco is once again open to visitors- come join the grand reopening! A variety of swinging masses with interesting behavior are just a few of the exhibits that await exploration and investigation.
Learn more about the physics of the slinky here: Exploratorium Science Snack
The slinky has been a popular toy since 1945! Read about the history and physics of the slinky, and the naval mechanical engineer that invented it on Wikipedia.
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Slinky Treadmill by @exploratorium: kinetic motion energy transfers to elastic potential energy and then back to kinetic energy in a cycling process as a slinky spring "walks" down an incline. Put the system on a treadmill, such as this one at the Exploratorium in San Francisco, and the walking behavior can be explored for many minutes. Note that after a while the slinky's walking becomes erratic.? With special thanks to the Exploratorium!
The exhibit features a very massive block of concrete to provide inertia to the base:
Wikipedia has the details on the physics of bouncing objects.
And the Exploratorium "snack" on the application of this physics to sports: Bouncing Baseballs.
Bouncing Ball @exploratorium : a steel ball bounces more than 230 times (counted using slow motion video) before coming to rest in this exhibit demonstrating the physics of a high coefficient of restitution. The bottom plate is amorphous steel and attached firmly to a massive block of concrete to enable the ball to retain as much kinetic energy as possible after each collision. ? With special thanks to the Exploratorium!
Spindrift @exploratorium: surprisingly complex and graceful motions arise when rings are set to roll on a parabolic surface in this exhibit created by artist Shawn Lani at the Exploratorium in San Francisco. As the energy of the ring's center of mass trades to and fro from potential to kinetic, odd motions such as flip-flops, figure eights, and quick spins can occur in a determined but chaotic fashion. ? With special thanks to the Exploratorium!
String Hyperboloid @exploratorium : 26 strings held straight by hanging weights can be rotated as a set to produce a hyperboliod- the quadric surface related to the revolution of hyperbola around its axis of symmetry. Note that although this 3D shape is curved, an a infinite set of straight lines (like those of the strings) lie on its surface. Turning the top disk of this exhibit raises the weights on each string so that when it is released the potential energy will transfer back and forth to kinetic energy of rotation until the energy is damped out due to friction. ? With thanks to the Exploratorium!
Some interesting history of the Turntable, one of longest running exhibits at the Exploratorium.
Turntable @exploratorium : rolling disks on a spinning platform. The path of each disk depends on position and angle at launch. Interesting orbits result from the interplay of angular momentum and gravity in this interactive exhibit. ? With special thanks to the Exploratorium!
Wikipedia has a nice introduction to the Zeeman Effect
Zeeman Effect on Mercury Green Emission Line @exploratorium: directly explore the Quantum Mechanics of electron spin with this amazing interactive exhibit. Excited Mercury gas emits a bright green line at 546nm (seen here as concentric circles using a Fabry-Perot interferometer) due to electrons transitioning between the quantized energy levels. We learn in chemistry that electrons come two to a shell with opposing spins (Pauli Exclusion). Indeed when the excited Mercury tube is placed in between magnets the green line splits, demonstrating that the electrons now have slightly different energies corresponding to the spin orientations interacting with the magnetic field. Advanced level quantum phenomena in a museum exhibit! ?With special thanks to the Exploratorium!
Make a similar device using CD cases: Step by step instructions in this Exploratorium Science Snack: Avalanche
Avalanche @exploratorium : Spontaneous stratification from pouring granular mixtures. Typically pouring stuff together results in further mixing, yet here the result is an ordered sorting into layers. The larger rounded dark grains separate from the smaller sharp-edged white grains forming the layers you see here. The darker grains alone would stack into a steeper pile (larger angle of repose) than the white which would form a less steep pile. An amazing physics discovery of the 1990s showcased here by Ken Brecher and Erik Thogerson.? With special thanks to the Exploratorium!
Read more about this exhibit here:
Exploratorium Science Snack: Water Spinner
Water Spinner @exploratorium : The parabolic surface of a contained liquid under the combination of centripetal acceleration and the pull of gravity. Centripetal acceleration increases proportional to the distance from the axis of rotation, so the liquid stacks highest far from the center. Also, a faster spin rate results in a deeper and steeper parabola- note how the surface flattens out as the exhibit comes to rest. Additional physics- symmetric waves (from the sharp initial impulse) travel and reflect along the curved surface for the first few rotations until damped out via viscosity and friction. ? With special thanks to the Exploratorium!
Kinetic Art by artist in residence Ned Kahn
Circling Wave Umbrella @exploratorium: kinetic art that produces mesmerizing wave structure in a disk of fabric. Follow the white dot on the bottom of the fabric to see the actual rotation rate of the disk. The stretchy vinyl coated spandex is set to spin at about 60 RPM which sets up a dynamical interplay between the inertia of the fabric and air resistance, producing four waves that travel at about 20 RPM. Thus the waves rotate at about 1/3 the speed of the cloth. Similar rotational waves travel around the arms of galaxies! Created by Ned Kahn, long time artist in residence at the Exploratorium.?With special thanks to the Exploratorium!
Magnetic Fluid Patterns @exploratorium: a dark ferromagnetic fluid, trapped in a small gap between two plates of glass, reacts under the influence of a powerful magnetic field in this exhibit at the Exploratorium in San Francisco. The intricate and beautiful fluid patterns result from surface tension between the liquids competing with the ferrofluid attempting to align with the field lines of a strong magnet as it is positioned at different distances underneath. ? With special thanks to the Exploratorium!
The Cloud Chamber is one of the longest running exhibits at the Exploratorium, and one of my favorites.
Cosmic Rays in Cloud Chamber @exploratorium: Visualizing the invisible- we live in a constant rain of charged subatomic particles that pass through the atmosphere (and our bodies) at relativistic speeds. The fleeting white lines and streaks seen here mark the paths of these cosmic ray particles through amplification via a phase change. The cloud chamber, with refrigeration on the bottom and heater elements on top, creates a 10cm thick region of supersaturated alcohol vapor that is at a temperature below its condensation point. Energetic charged particles produce a trail of ions (atoms with an electron knocked off) and these ions become the center of the drops that form the white trails showing the path of the particles. ? With special thanks to the Exploratorium!
Sand Shaker @exploratorium: a thin layer of white sand is subjected to vibrations on top of a circular plate in this exhibit created by artist Charles Sowers at the Exploratorium in San Francisco. When granular substances like sand are rapidly shaken, they often take on the properties of fluids through a process called vibrofluidization. Strange non-Newtonian fluid behavior is seen in this sand when the frequency of vibration is adjusted to 16Hz (shown here in 240fps slow motion)- amazing complexity arising from simple and regular motion! ? With special thanks to the Exploratorium!
Catenary Arch @exploratorium : when an arch is built in the shape of this special mathematical curve (even with slippery blocks) the compression forces between each block are always parallel to the curve- the stack is stable with no tendency to buckle. The catenary is the exact shape of a chain hanging by its ends, also known as the hyperbolic cosine. Famously used in architecture, from the buttresses of Notre Dame to the Gateway Arch. ?With special thanks to the Exploratorium!
"All Eyes om Me" Exhibit
The physics and design of this exhibit is very similar to what is depicted in this image:
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Fresnel Mirror Array @exploratorium : 360 mirrors arranged to reflect to a single focal point in this exhibit entitled “All Eyes on Me”. A mirror version of the Fresnel lens, where each concentric ring of mirrors is slanted toward the center, with the lager rings slanted more, such that the full assembly acts like a parabolic mirror.?With special thanks to the Exploratorium!
Magnetic Pendulum Array @exploratorium: 21 aluminum pendulums, each with a large magnet affixed to the end. The magnets allow kinetic energy to be shared. Note how the energy of the end pendulum is transferred to the rest in two steps- 1) the magnetic fields interact to damp the motion until 2) the end pendulum is captured into synchronized motion with the rest, allowing the energy to propagate to the front pendulum. ? With special thanks to the Exploratorium!
Frank Oppenheimer, founder of the Exploratorium Museum, demonstrates the sand pendulum display in these images from the 1970s.
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Sand Pendulum @exploratorium: a swinging pendulum maps out a beautiful sine curve on to a conveyor belt. The belt moves at constant speed such that the sand creates a graph of the pendulum’s position as a function of time. With special thanks to the Exploratorium!