Physics Toy Store 28


Diffractive Optical Element Sample
View this post on Instagram

Diffractive Optical Element: images produced by constructive and deconstructive interference of coherent laser light. The patches of microstructure on the surface of this transparent plastic are far field holograms- transmission holograms, but with the image at infinity. Side by side images from two different laser wavelengths (red 635 nm, green 520 nm) shows clearly the red image is larger than the green since diffraction angle is proportional the wavelength. So much physics here! ➡️ Follow the link in my profile for info on where to obtain this and other amazing items featured here on @physicsfun #holidayspecs #holospecs #transmissionhologram #hologram #holographic #earth #physics #physicstoy #diffraction #laser #optics #diffractiveopticalelement #science #constructiveinterference #encoding #scienceisawesome

A post shared by physicsfun (@physicsfun) on

Amazing application of high resolution far field holograms. The only available source I know of for projection holograms at this high resolution is this supplier of industrial samples

From MaterialSampleShop.com: Diffractive Optical Element Sample

Need a laser pointer? Incredibly, you can get 3 (one of each color) for under $10 (including S&H):

From eBay: BUY NOW
Laser Pointer- Set of 3 Colors



Air Stream Levitation
Similar device available here (comes with disks):

From Amazon: BUY NOW
Air Stream Levitation


Here are some Styrofoam balls that will levitate with this device:

From Amazon: BUY NOW
Foam Spheres



Hyperbola Hole mechanical toy
Available here in many colors:

From Make Anything: Hyperbola Hole Toy

Please see next video and links for more hyperboloid toys!


Pencil Hyperboloid
Choose your color and get one here:

From Etsy: BUY NOW
Hyperboloid Pencil Holder


don't forget a set of pencils:

From Amazon: BUY NOW
Colored Pencil Sets



Hyperboloid Spinner
Available here:

From Amazon: BUY NOW
HypnoGizmo

From eBay: BUY NOW
HypnoGizmo

Ringer Box and Telephone Magneto
View this post on Instagram

Ringer Box and Telephone Magneto: a functioning antique 5 bar telephone magneto generator (made in 1910!) creates alternating current which energizes the twin solenoids of the ringer box. The copper wire coils in the solenoids (green cylinders) become electromagnets which flip their north and south poles with each cycle of the AC current. The flipping magnetic fields at the ends of the coils pull the metal clapper back and forth ringing the bells. Back in 1910 only 40% of US homes had electricity so these generators were used to ring bells up to 20 miles away! With sufficient cranking speed this generator can create more than 280 Volts AC peak to peak using the characteristic horseshoe shaped magnets (bars) which provide the induction field. ➡️ Follow the link in my profile for info on where to get a vintage magneto and other amazing things featured here on @physicsfun #telephony #AC #light #physics #magneto #telephonemagneto #physicstoy #magneticinduction #generator #alternator #voltagedivider #science #scienceisawesome

A post shared by physicsfun (@physicsfun) on

Vintage ringer boxes are available here (see next video for antique magneto generators):

From eBay: BUY NOW
Antique Ringer Box



Wikipedia has a nice description of the physics and mechanics of these electric bells.


Vintage Telephone Magneto
View this post on Instagram

Vintage Telephone Magneto: a functioning antique 5 bar telephone magneto generator- made in 1910! As indicated by the neon bulb voltage divider- with sufficient cranking speed this generator can create more than 280 Volts AC peak to peak using the characteristic horseshoe shaped magnets (bars) to provide the induction field. The AC current is of a low frequency as indicated by the flickering bulbs. Back in 1910 only 40% of US homes had electricity so these generators were used to ring telephone bells up to 20 miles away! ➡️ Follow the link in my profile for info on where to get a vintage magneto and other amazing things featured here on @physicsfun #telephony #AC #light #physics #magneto #telephonemagneto #physicstoy #magneticinduction #generator #alternator #voltagedivider #science #scienceisawesome

A post shared by physicsfun (@physicsfun) on

vintage magnetos are available here:

From eBay: BUY NOW
Bar Magneto Generator



Spinner Fidget Trick
View this post on Instagram

Spinner Fidget Trick: defy gravity!- a trick to try with a fidget spinner you might have in a drawer somewhere. For the trick to work the spinner needs to have most of its mass far from the center (not all spinners will work)- and you may need to drill a hole down its center to attach an axle. This Spinpal spinner has three heavy steel spheres placed to maximize rotational inertia, that along with precision bearings, gives this fidget toy properties of a quality gyroscope. Give the spinner significant RPMs and it will suspend from, and precess around, a string! Thanks to @spinpal for sending me this a while back. ➡️ Follow the link in my profile for info on where to get many of the amazing items featured here on @physicsfun #physics #physicstoy #spinner #spinningtop #rotationalinertia #fidgettoy #gyroscopic #fidget #science #angularmomentum #precession #gyroscope

A post shared by physicsfun (@physicsfun) on

See the next video of a gyroscope that will perform the same trick!


Precession of a Gyroscope
Get one here:

From Amazon: BUY NOW Gyroscopes
From eBay: BUY NOW Gyroscopes


Perspective Puzzle
Vintage puzzles in this series are available on eBay:

From eBay: BUY NOW Virtual Illusion 3D Puzzle


Spin Top Carousel
View this post on Instagram

Spin Top Carousel: two spin tops of the same mass hang balanced on the ends of a beam such that their rotational motion is allowed to transfer to the system as a whole. The tops are set to spin as usual, but here small neodymium magnets are embedded in the tops of their stems which allows them to connect and hang from metal pins in the beam. The physics of how the angular momentum of the tops is transferred to the rotation of the system of this new toy is still under study. Made by German artisan Kurt Juergen Weigl. 🌟Special thanks to physicist Christian Ucke for his help in obtaining this beautiful top for my collection. ➡️ Follow the link in my profile for more info on this top and where to get many of the amazing items featured here on @physicsfun #physics #physicsfun #physicstoy #spintop #spinningtop #angularmomentum #balance #neodymiummagnets #rotationalkineticenergy #conservationofangularmomentum #topcarousel #science #scienceisawesome

A post shared by physicsfun (@physicsfun) on

The artisan that creates this toy, Mr. Weigl, does not have a online store, but does have a link to where he can be contacted which is provided below (all in German).
Unique Art - the page of Kurt Weigl


Trihexaflexagon
Print and construct one from templates available here:

From Puzzles.com: Flexagon Templates

Learn more about these paper mathematical mechanical wonders- featured in these books by Martin Gardner:

From Amazon: BUY NOW
Gardner Books: math, projects, puzzles



Tork Kinetic Sculpture
View this post on Instagram

Tork Kinetic Sculpture: the motion of this 1975 vintage kinetic art may seem random at first, but it is actually three modes of motion combined in this coupled harmonic oscillator. The shape of the spring equally allows for forward/backward oscillations and side to side oscillations, when launched it will trade back and forth between these two modes producing a Lissajous curve. Superimposed is a vertical oscillation adding a comical touch. Produced and patented(1970) by Donald Max Engleman of Kinetic Objects Inc. ➡️ Follow the link in my profile for more info and where to get the amazing items featured here on @physicsfun #coupledoscillator #tork #hamonicoscillation #hookeslaw #spring #kineticart #physics #physicstoy #science #scienceisawesome #kineticsculpture

A post shared by physicsfun (@physicsfun) on

This item from the 1970s is sometimes available on eBay:

From eBay: Search NOW
Tork Kinetic Sculpture



See the patent here: US3516193


Random Dither Image Encryption
View this post on Instagram

Dither Image Encryption: three images hidden in random dither patterns are revealed by precisely overlaying and aligning any two patterns in the generated set. Amazingly each pattern holds two encrypted images where b+c=♣, a+b=♦, and c+a=♥. These patterns were created by Dithercrypt, a shared python script created by Andy Lutomirsky. The concept of entropy is shared between physics and cryptography, and gives a measure of the randomness inserted and strength of the key. ➡️ Follow the link in my profile to access the mentioned python code and for info on where to get the amazing items featured here on @physicsfun #physicsfun #physics #dither #cryptography #physicstoy #cipher #mathtoy #mathstoy #secretcode #science #scienceisawsome

A post shared by physicsfun (@physicsfun) on

I got this set as part of the Gathering 4 Gardner gift exchange. For those with coding skills- here's the python script:
From GitHub: Dithercript


Diamagnetic Racetrack
View this post on Instagram

Diamagnetic Racetrack: thin pyrolytic graphite sheets levitate above powerful magnets. A set of five concentric neodymium magnets, alternating N-S-N-S-N comprise the racetrack and form the trapping field. Diamagnetic substances develop temporary repulsive magnetic fields only when they are in the presence of a magnetic field from some other source. Graphite of this sort is the most diamagnetic substance known. ➡️ Follow the link in my profile for info on where to buy this and other amazing items featured here on @physicsfun #diamagnetic #diamagnetism #magnetism #magnets #magneticfield #physics #physicstoy #levitation #neodymium #pyrolytic #graphite #pyrolyticgraphite #electromagnetism #science #scienceisawesome

A post shared by physicsfun (@physicsfun) on

Diamagnetic levitation kits are available here: the racetrack magnets are a bit pricey though!

From eBay: BUY NOW Diamagnetic Levitation Kit

Educational Innovations has this affordable starter kit:


From Educational Innovations: BUY NOW Diamagnetic Levitation Kit


Mercury Maze
These vintage items from the 1980s can be found on eBay and Etsy quite often (a few available as of this posting):

From eBay: BUY NOW
Mercury Maze

From Etsy: BUY NOW
Mercury Maze



Slinky Physics!
Get the classic here:

From Amazon: BUY NOW
Mini Slinky

Get a giant version of the slinky here!


From Educational Innovations: BUY NOW
Giant Slinky: Super Wave Spring


Acasta Gneiss Sphere
View this post on Instagram

Acasta Gneiss: this polished sphere is a sample of the oldest known rock on Earth- dated at 4.03 billion years old based on multiple and mutually consistent radiometric dating techniques. This rock is only found in the Northwest Territories of Canada and was collected by Yellowknife resident Mark Brown. Happy Earth Day 2019! ➡️ Follow the link in my profile for info on how to obtain a chunk of the oldest piece of Earth for yourself (and many other science curiosities) as featured here on @physicsfun #earthday #happyearthday #earthday2019 #radiodating #radioisotopedating #acasta #gneiss #physics #physicstoy #geophysics #geophysicstoy #mineral #oldestrock #acastariver #amazing #deeptime #science #scienceisawesome

A post shared by physicsfun (@physicsfun) on

nice samples of the verified oldest know Earth rock available here:

From eBay: BUY NOW
Acasta Gneiss Specimens


Wikipedia has the details on Acasta Gneiss and see the next video and links for more geophysics fun!


Peridotite Xenoliths: Samples of Earth's Mantle
View this post on Instagram

Peridotite Xenoliths: here before you are chunks of Earth's mantle material from 50 kilometers or deeper below the surface, far below the deepest hole ever drilled at 12.3 km (a great effort which didn't even break through to the mantle). However, green peridotite crystals of olivine and pyroxenes are sometimes brought to the surface by viscous lava in the form of xenoliths- inclusions in the volcanic basalt as seen in this sample. This piece was collected from Peridot Mesa in the San Carlos Volcanic Field of AZ. Amazing sample of the inaccessible Earth's interior. ➡️ Follow the link in my profile for more info and how to buy a piece of the Earth's mantle material and other amazing items featured here on @physicsfun #geology #rockhound #geophysics #geophysicstoy #mantlexenolith #xenolith #physics #physicstoy #peridotite #olivine #peridot #mineral #volcanic #lava #science #scienceisawesome

A post shared by physicsfun (@physicsfun) on

nice and inexpensive samples available here:

From eBay: BUY NOW
Mantle Xenolith Peridotite sample



Cartesian Diving Devil
View this post on Instagram

Cartesian Devil: strange blown glass Cartesian diver- water enters and exits through its tail which is wrapped sideways around it, so when the pressure is released the water devil spins. Pressure on the bottle cap forces water into the diver, which compresses the bubble in its head allowing it to sink. When the pressure is released the bubble regains its size expelling the water through the tail and the devil spins and rises. Featured on the Wikipedia page on Cartesian divers. ➡️ Follow the link in my profile for info on where to buy this and many other curiosities featured here on @physicsfun #waterdevil #glass #glassblowing #fluidstatics #cartesiandiver #physicsfun #buoyancy #Archimedesprinciple #physics #physicstoy #pascalsprinciple #science #scienceisawesome

A post shared by physicsfun (@physicsfun) on

Available here:

From eBay: BUY NOW Cartesian Devil Diver


Extreme Viscosity Kinetic Sculpture
View this post on Instagram

Extreme Viscosity Sculpture: a heavy ball bearing descends through a very viscous fluid while a bubble of air ascends in this weird and wonderful vintage kinetic art desk toy I found on eBay. It takes almost two full minutes for the ball to move to the bottom as the air bubble moves to the top- shown here at 2X speed to fit the Instagram time limit. Note the strange phenomena that occurs when the ball bearing passes by the bubble. ➡️ Follow the link in my profile for info on where to buy many of the physics toys featured here are on @physicsfun #kineticart #viscosity #drag #viscous #fluiddynamics #physicsfun #gravity #physics #physicstoy #bubble #buoyancy #Archimedesprinciple #science #art #desktoy #scienceisawesome

A post shared by physicsfun (@physicsfun) on

This vintage object seems to be from the 1980s and is a rare find on eBay. See the next videos for objects with similar physics.


Fluorescent Ooze Tube with UV Laser
View this post on Instagram

Fluorescent Ooze Tube with UV Laser: stunning visual effects from a 405 nm laser pointer interacting with the viscous polyisobutene fluid in this ooze tube timer toy. The fluorescent dye converts the UV laser light to visible green light as the fluid stretches into thin ropes that act as light pipes while bubbles reflect and fan the beam. Perhaps the next generation Lava Lamp? ➡️ Follow the link in my profile for info on where to get this and many of the amazing items featured here on @physicsfun #ropecoil #viscosity #fluiddynamics #fluidmechanics #physics #physicstoy #405nmlaser #laserpointer #fluorescent #lightpipe #internalreflection #fluorescence #viscousbuckling #liquidrope #liquidropecoileffect #ooze #oozetube #coileffect #kineticart #science #scienceisawesome

A post shared by physicsfun (@physicsfun) on

See next video below for ooze tube sources (green works best). Get an inexpensive UV laser pointer here:

From Amazon: BUY NOW
UV (405 nm) Laser pointer




The Ooze Tube
View this post on Instagram

Ooze Tube: viscous polyisobutene fluid timer toy. Some interesting physics phenomena are found in this kinetic art novelty item: the "liquid rope-coil effect" where the fluid thread coils and stacks as it lands on the pooling surface, and a curious periodicity in the rate of flow that is related to the formation of non-spherical bubbles as the air and fluid trade places (shown in time-lapse). The physics of the coiling effect is complex (see the link in my blog). Broadly speaking the coiling is due to the bottom of the fluid rope widening at the contact point with the surface, and as it widens the fluid slows down but not evenly. This uneven rate of flow produces a bend and the elasticity of the stream constrains the rope to a limited radius- hence a stack of coils. ➡️ Follow the link in my profile for info on where to get this and many of the amazing items featured here on @physicsfun #ropecoil #viscosity #fluiddynamics #fluidmechanics #physics #physicstoy #viscousbuckling #geophysics #helix #helicalcoil #liquidrope #liquidropecoileffect #ooze #oozetube #coileffect #kineticart #science #scienceisawesome

A post shared by physicsfun (@physicsfun) on

Many colors (and two sizes) to choose from:


From Educational Innovations: BUY NOW
Ooze Tube

From Amazon: BUY NOW
Ooze Tube


The physics of the liquid rope-coil effect is pretty complex. Here is a recent scientific paper on the topic with nice illustrations.

Journal of Fluid Mechanics: Multiple coexisting states of liquid rope coiling


Miniature Van de Graaff Generator
View this post on Instagram

Van de Graaff Generator: this miniature electrostatic generator can create potentials of more than 50,000 volts allowing sparks to jump a couple centimeters through dry air. Similar physics to the sparks created when shoes scuff on carpet, a moving rubber dielectric belt carries electrons away from the top sphere leaving it positive charged- as can be seen by the electrostatic repulsion of some Mylar strands. A small battery powered 3V motor drives the belt via the bottom pulley in this unit that costs less than $10 US. With appreciation to @educational_innovations for sending me this device. ➡️ Follow the link in my profile for info on where to buy this device and other amazing items featured here on @physicsfun #physics #physicstoy #physicsfun #electrostaticdischarge #electricity #staticelectricity #electromagnetism #vandegraaff #vandegraaffgenerator #breakdownvoltage #spark #electrostatics #highvoltage #science #scienceisawesome #dielectric #triboelectric #triboelectriceffect

A post shared by physicsfun (@physicsfun) on


This device is sold as the "Static Shocker" hands on lab. Get one here for $8.95! :


From Educational Innovations: BUY NOW Static Shocker Mini Van de Graaff

The device can use an empty aluminum can for the top electrode which works- but this $9 hollow steel sphere looks and works even better- I used the 80mm sphere:

From eBay: BUY NOW Hollow Steel Sphere


Vintage Flicker Bulb
View this post on Instagram

Vintage Flicker Bulb: the flexible 15 Watt carbon filament in this bulb oscillates back and forth producing a slight resemblance to a flickering flame. A magnet attached to the side of the bulb pushes on the magnetic field produced by the current flowing in the filament. Since US house mains current is AC at 60 Hz the current flow changes direction many times a second which in turn allows the magnet to push the filament back and forth at the same rate. Magnetic fields can add and subtract- here a strong magnet is used to temporarily make the filament go into chaotic oscillations. Light bulb physics! ➡ Follow the link in my profile for info on where to buy bulbs like this one and other amazing items featured here on @physicsfun #flickerbulb #electricflame #AmperesLaw #magnets #magneticfield #magnetism #electromagnetism #filament #lightbulb #flickerflame #physics #physicstoy #noveltybulb #science #scienceisawesome

A post shared by physicsfun (@physicsfun) on

Similar bulbs available here while supplies last:

From eBay: BUY NOW Flicker Flame Bulb


Superellipsoid
View this post on Instagram

Superellipsoid: the "super egg" is a mathematical creation of Danish scientist and artist Piet Hein (also the inventor of the Soma cube puzzle). The equation of the superellipse is that of a regular ellipse, but raising both sides to the power of 2.5 instead of 2- the resulting curve had a flattened end that allows the superellipsoid to stand upright. The superelljpse has found use in architecture and design. This super egg is made of stainless steel. ➡️ Follow the link in my profile for info on where to buy this and other amazing items featured here on @physicsfun #science #math #art #mathtoy #mathstoy #PietHein #Hein #physics #physicstoy #superellipse #superegg #volumeofrevolution #ellipse #somacube #SergelsSquare

A post shared by physicsfun (@physicsfun) on

Vintage Super Eggs of Piet Hein can be found on eBay:

From eBay: BUY NOW
Superellipsoid by Piet Hein


Get one in brass from this shop:

From Etsy: BUY NOW
Brass Super Egg



Ambiguous Object

These type of objects were invented by mathematician Kokichi Sugihara, and you can buy his books here:

From Amazon: BUY NOW Ambiguous Objects by Kokichi Sugihara

Some 3D prints are available from many makers here:

From eBay: BUY NOW Ambiguous Objects


From Amazon (Japan): BUY NOW set of four ambiguous objects with booklet
This kit contains four white plastic illusion objects (including the arrow) and a booklet. I used the translate feature in the Chrome browser to place my order and it shipped to California in a few days.

The math and physics are described here in this technical journal article by Prof. Sugihara.


Ambiguous Object Illusion Mug
Available here

From eBay: BUY NOW Squirkle Mug Ambiguous Object Illusion


Tornado Spheres
View this post on Instagram

Tornado Spheres: two ball bearings welded together can be made to spin up to 2000+ rpm by the Magnus Effect using a stream of air. Shining three colored LEDs on the spinning pair produces an illusion of floating rings along with a second illusion that these rings are rotating and changing direction due to aliasing with the frame rate of the video camera (like the famous wagon-wheel effect). ➡️ Follow the link in my profile for info on where to buy this and many other amazing items featured here on @physicsfun #spin #rpm #tornadospheres #hurricaneballs #angularmomentum #physics #physicstoy #physicsfun #magnus #magnuseffect #torque #rotation #rotationalinertia #amazing #concavemirror #science #aliasing #wagonwheeleffect #scienceisawesome

A post shared by physicsfun (@physicsfun) on

Get a set here:

From eBay: BUY NOW Tornado Spheres
Get a concave mirror like the one in the video for less than $3 here:

From eBay: BUY NOW Concave Mirror
And get a set of inexpensive colored lights here:

From eBay: BUY NOW Color LED lights


Corona Discharge Trajectories
View this post on Instagram

Corona Discharge Trajectories: the ejected electron stream propels the end of a thin wire connected to a miniature Tesla coil. The corona discharge creates a glowing plasma at the end of the wire, but also imparts momenta that pushes the wire’s end into a final state circular orbit. The more interesting behavior occurs during the initial transient orbits which seem to be hypotrochoid type curves beautifully captured here using the Slow Shutter app. Please see seven posts back for details about this mini Tesla coil. ➡️ Follow the link in my profile for info on where to get this Tesla coil with wire end attachment and many other amazing items featured here on @physicsfun #physics #physicsfun #physicstoy #tesla #teslacoil #resonance #transient #transientmotion #resonantfrequency #resonanttransformer #highvoltage #coronadischarge #highfrequency #oscillations #inductance #coppercoil #science #rccircuit #scienceisawesome

A post shared by physicsfun (@physicsfun) on

Mini Tesla coil with wire end attachment:

From Amazon: BUY NOW
Mini Tesla Coil


Long exposure image captured using this Slow Shutter app:

From App Store: BUY NOW
Slow Shutter Cam - Cogitap Software


see videos and links below for more information and uses of this mini Tesla Coil


Gas Collection for Emission Spectra
View this post on Instagram

Gas Collection for Emission Spectra: pure samples of hydrogen, nitrogen and five Nobel gasses are subjected to the high frequency pulsed field of a miniature Tesla coil. Each gas has a characteristic breakdown voltage and emission spectrum- note that Nitrogen has the highest breakdown voltage and only glows when very near the coil where the field is most intense whereas Neon and Helium have the lowest breakdown voltage and begin to glow many centimeters away from the coil. The color of each gas is due to a mix of the colors emitted from electron energy transitions specific to each element- the basis of spectroscopy. The Krypton tube also exhibits interesting oscillations with this particular Tesla coil. ➡️ Follow the link in my profile for info on where to get this set and many other amazing items featured here on @physicsfun #neon #hydrogen #nitrogen #helium #argon #krypton #xenon #gascollection #emissionspectra #excitation #spectra #breakdownvoltage #paschenslaw #glowdischarge #glowdischargetube #teslacoil #highvoltage lightbulb #science #scienceisawesome

A post shared by physicsfun (@physicsfun) on

I made the display holder and I got this set of gas tubes here (about $7 per tube):

From eBay: BUY NOW
Gas Pure Element Samples


The breakdown voltages of the elements featured in this post are described by Paschen's Law:

Here is a excellent article with an overview of the physics of glow discharge and its application in lighting and other technologies.

See next video and links for where to obtain the mini Tesla coil


Miniature Tesla Coil
View this post on Instagram

Tesla Coil: miniature low current version of the famous air core double-tuned resonate transformer invented by Nikola Tesla in 1891. The thick copper of the primary coil is set into three windings around the many windings of the tall secondary coil. This one uses a modern transistor circuit to excite the radio frequency oscillations that produce a voltage in excess of 50kV in the form of pulses that cycle about 100k times a second. This version is fed by a 24V DC power supply and is fairly safe due to a low current (mA)- but the circuitry does get hot and demands a huge heat sink with fan (the metal base can burn skin when operating). The coils comes with attachments- the spike produces a purple corona discharge as the voltage exceeds the breakdown voltage of air with current flowing into the air or arcing over to a grounded piece of metal. The corona discharge imparts momenta, and here the ends of a bent wire are set into rotation from the slight push of the escaping electrons. ➡️ Follow the link in my profile for info on where to get this Tesla coil and many other amazing items featured here on @physicsfun #physics #physicsfun #physicstoy #tesla #teslacoil #resonance #resonantfrequency #resonanttransformer #highvoltage #coronadischarge #highfrequency #oscillations #inductance #coppercoil #science #rccircuit #scienceisawesome

A post shared by physicsfun (@physicsfun) on

For the price, this is the best one on the market I think and beautiful to look at in copper- the music function does not do much, but it is a great little Tesla coil and it comes with three accessories for the top. Please be sure to employ all appropriate safety precautions when utilizing any electrical circuity!

From Amazon: BUY NOW
Mini Tesla Coil


Wikipedia has the details on the essential basic physics and design of Tesla Coils



Click here for more:
Physics Toys,


UA-63736203-2

No comments: