This simple demonstration shows the power of surface tension, especially at small lengthscales. Another way to break the surface tension holding the water in the sieve would be to spray the top of the jar with soapy water. The soap acts as surfactant, decreasing the surface tension such that the water is unable to counteract the force of gravity.
Tag: physics
Impinging Without Coalescing
Three impinging jets of silicone oil rebound without coalescence due to thin-film lubrication between the jets. The motion of the oil replenishes the thin layer of air separating the streams. The same phenomenon keeps droplets from coalescing as well. (Photo credit: BIF Lab, Department of Engineering Science and Mechanics, Virginia Tech) #
Blast Waves
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Watch closely in this high-speed video of a bomb exploding and you will see the spherical blast wave moving outward as a visual distortion. The increase in temperature caused by the leading shockwave changes the index of refraction of the air, bending the light and distorting our view of the background. The mechanism is similar to schlieren photography, which has been used for more than a century to capture images of compressible flows.
Guinness Physics
Take a look at the physics of a pint of Guinness, including the formation of foam, the circulation of bubbles, and the importance of nitrogen and surfactants. The Physics of Fluids paper the host refers to is available here. (And, yes, I will admit to debating the physics occurring in my pint glass while in a pub.) # (via Martin)
Sound and Harmonics
The vibrations we perceive as sound, whether in air, water, or any other fluid, are tiny pressure waves emanating from a source, transmitting like ripples across a pond, and finally being caught by our ears and translated by our brains. In this video, the mechanisms and mathematics of sound and harmonics are explained. Although we’re most familiar with these concepts in acoustics, the same principles are used when studying other oscillatory motions, including pendulums, mass-spring systems, disturbances in boundary layers, and the vibrations of a diving board. All of these things rely on the same fundamental principles and mathematics.
Feynman: The Universe in a Glass of Wine
Some wisdom for you this Friday from the incomparable Richard Feynman:
A poet I think it is who once said the whole universe is in a glass of wine. I don’t think we’ll ever know in what sense he meant that for the poets don’t write to be understood. But it is true that if you look at a glass of wine closely enough, you’ll see the entire universe.
There are the things of physics: the twisting liquid, the reflections in the glass, and our imagination adds the atoms. It evaporates, depending on the wind and weather. The glass is a distillation of the earth’s rocks and in its composition, as we’ve seen, the secret of the universe’s age and the evolution of the stars. What strange array of chemicals are in a wine? How did they come to be? There are the ferments, the enzymes, the substrates and the products, and there in wine was found great generalization: all life is fermentation. Nor can you discover the chemistry of wine without discovering, as did Pasteur, the cause of much disease. How vivid is the claret, pressing its existence into the consciousness that watches it?
And if our small minds for some convenience divides this glass of wine, this universe, into parts: to physics, biology, geology, astronomy, psychology and all, remember that nature doesn’t know it. So we should put it all back together and not forget at last what it’s for. Let it give us one final pleasure more: drink it up and forget about it all.
(submitted by @jerrodh)
White Hole Analogues
A white hole–the cosmological opposite of a black hole–is a singularity from which matter emerges but which matter can never enter from beyond the event horizon. Hydraulic jumps, those rings that sometimes appear in the kitchen sink, turn out to be a physical analog of this behavior. The photo above shows a hydraulic jump with a needle placed inside the event horizon. In the wake of a needle, there’s a Mach cone, just like when an object moves faster than the speed of sound. For more, see the Photonist. (via freshphotons)
Note that we mentioned this item a few months ago, but the full paper has just been published.
DIY Non-Newtonian Fluids
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We’ve featured the non-Newtonian fluid oobleck here before, but it bears repeating as a fun and easy exercise for anyone to do at home or at school, especially with kids. For extra fun, try vibrating it, using it as liquid armor, or filling a pool and walking on it.
How Not to Get Wet in the Rain
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Ever wonder how to minimize how wet you get if you’re caught in the rain without an umbrella? This lecture discusses just that problem and how to calculate an answer. I actually solved a version of this problem when studying for my PhD quals, only I first had to determine the terminal velocity of a rain drop (~10 m/s assuming a 4mm spherical drop) and work from there. We also had to compare moving upright to running at an angle. It makes for an interesting little diversion. (via physicsphysics)
The ABCs of Physics
b=buoyancy is part of Ashley JM’s photo set The ABCs of Physics. In her words:
Buoyancy is what causes less dense objects to float in a more dense fluid, such as a helium balloon in air. There is a buoyant force that pushes up on the object, equal to the weight of the displaced fluid.
That little diagram up there is called a force diagram, they can be even more daunting than equations at times. This one shows that the buoyant force up on the balloon is equal to the force of tension in the string, this keeps the balloon in equilibrium.
Be sure to look at the rest of her physics photos! # (via physicsphysics)
