Budget physics

Quantum Re-Excitation: Phosphorescence 

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Quantum Re-Excitation: a green laser should not normally be able to induce a phosphorescent glow, but if the material is already excited a green laser can re-excite it as seen here. Glow-in-the-dark phosphorescence is a quantum mechanical phenomenon where high energy photons (like those from a near UV laser pointer) are absorbed by electrons which are then boosted to higher energy levels. The glow comes from these electrons emitting lower energy photons (green in this case) as they jump down through a series of energy levels back towards their ground state. If an electron is only partially down the cascade path, lower energy photons from a green laser can bump it back up to the excited state. Quantum mechanics is all about discrete jumps in energy like what is happening here. 

Einstein's Drinking Bird Toy

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Wikipedia has wonderful details about the rich history (and further descriptions of the operational principals) of the Drinking Bird

Einstein’s Drinking Bird: this antique drinking bird toy was made in 1946, and this exact version sat on the kitchen table of Albert Einstein where many reports by friends and family told how the famous physicist was greatly amused by it, and that over a period of a few weeks he figured out its hidden operating principles. It turns out that this classic physics toy is a functional heat engine (swipe to see a familiar modern version) where cooling by evaporation at the head/beak leads to lower pressure in the top bulb, the pressure in the bottom bulb pushes the dichloromethane fluid (here dyed red) up the neck making the bird top heavy and the bird tips over dipping its beak and letting the fluid return to the bottom bulb. The process repeats, and as long as the top bulb stays wet and cooler than the bottom this heat engine will continue to cycle. 

Bouillant de Franklin (Hand Boiler)

A variety of shapes and colors are available 
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Bouillant de Franklin (Hand Boiler): reversible liquid-gas phase transition device made famous by Benjamin Franklin who was one of the first to describe the physics of its operation. The boiling point of dichloromethane is slightly below body temperature - heat from a hand increases pressure in the bottom bulb pushing the green (dyed) liquid through the glass pipe to the top. A vintage handmade version from France.

Nautilus Spiral Gears

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Nautilus Spiral Gears: an extreme example of non-circular gear sets. This set is based on the famous Fibonacci spiral and evokes the cross section of nautilus shell with internal chambers. If one gear of this set is turned at constant speed, the other will turn with an varying speed. A 3D print of Misha Tikh and the research of Balint et al. 

Phonotrope Spinning Gears

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Phonotrope Spinning Gears: one more amazing phonotrope from apyrodesign. When the rate of rotation matches the rate of the smartphone video process (wait for it) twelve animated gears appear to mesh and turn. The precision laser cut acrylic is specifically designed to interact with the video process, similar to the animation effect of a flip book, but in a repeating cycle like that of the phenakistiscope, the 1833 invention that started moving media animation that lead to the development of movies and video.