Sloshing is a problem with which anyone who has carried an overly full cup is familiar. Because of their freedom to flow and conform to any shape, fluids can shift their shape and center of mass drastically when transported. The issue can be especially pronounced in a partially-filled tank. The sloshing of water in a tank on a pick-up truck, for example, can be enough to rock the entire vehicle. One way to deal with sloshing is actively-controlled vibration damping - in other words, making small movements in response to the sloshing to keep the amplitude small. This is exactly the kind of compensation we do when carrying a mug of coffee without spilling. (Image credit: Bosch Rexroth; source)
There are five special points where a small mass can orbit in a constant pattern with two larger masses (such as a satellite with respect to the Earth and Moon). The Lagrange Points, named in honor of Italian-French mathematician Joseph-Louis Lagrange, are positions where the gravitational pull of two large masses precisely equals the centripetal force required for a small object to move with them. This mathematical problem, known as the “General Three-Body Problem” was considered by Lagrange in his prize winning paper (Essai sur le Problème des Trois Corps, 1772).
The five Sun–Earth Lagrangian points are called SEL1–SEL5, and similarly those of the Earth–Moon system EML1–EML5, etc. Orbits around Lagrangian points offer unique advantages that have made them a good choice for performing certain spacecraft missions. For example the Sun–Earth L1 point is useful for observations of the Sun, as the Sun is always visible without obstructions by the Earth or the Moon. SOHO, the ESA/NASA solar spacecraft is positioned there. read descriptions about invidual L-points here
Soap bubbles are ephemeral creations. The slightest prick will send them tearing apart in the blink of an eye. It may come as a surprise, therefore, that dropping a water droplet through a bubble will not break it. Instead, the bubble will heal itself using the Marangoni effect. In a soap bubble, the soap molecules act as a surfactant, lowering the surface tension of the water and allowing the fragile structure to hold together. When the water drop impacts the bubble, the local surface tension increases because of the relative lack of soap molecules. This increase in surface tension pulls at the rest of the bubble, drawing more soap molecules toward the point of contact. The effect evens out surface tension across the surface and stabilizes the bubble. You can test the effect at home, too. If you wet your finger, you can poke a soap bubble without popping it. (Video credit: G. Mitchell; via io9)
The evil geniuses at NASA Ames Research Center are trying to create super intelligent soccer balls with a top-secret vaporized serum! … er … wait, no. They’re just studying the aerodynamics of the official World Cup ball - the “Brazuca.”
The mass of quantum particles is fundamentally unknowable
"This is because there’s that same inherent tension-and-uncertainty between energy and time as there is between position and momentum! So if you have a very small uncertainty in the timescale of a particular system, there must inherently be a very large energy uncertainty.
Think about this in terms of a particle’s lifetime, now. If a particle stably (or quasi-stably) exists for a very long period of time, its energy uncertainty can be very small. But what of an inherently short-lived, very unstable particle? Its energy uncertainty must be huge to compensate; Heisenberg demands it.
And now for the kicker: if there’s a large uncertainty in a particle’s inherent energy, and we know that there’s an energy-mass equivalence via E = mc^2, then the shorter a particle’s lifetime is, the less well-known its mass can be, even in principle!”
Like many sports, the gameplay in football can be strongly affected by the ball’s spin. Corner kicks and free kicks can curve in non-intuitive ways, making the job of the goalie much harder. These seemingly impossible changes in trajectory are due to airflow around the spinning ball and what’s known as the Magnus effect. In the animation above, flow is moving from right to left around a football. As the ball starts spinning, the symmetry of the flow around the ball is broken. On top, the ball is spinning toward the incoming flow, and the green dye pulls away from the surface. This is flow separation and creates a high-pressure, low-velocity area along the top of the ball. In contrast, the bottom edge of the ball pulls dye along with it, keeping flow attached to the ball for longer and creating low pressure. Just as a wing has lift due to the pressure difference on either side of the wing, the pressure imbalance on the football creates a force acting from high-to-low pressure. In this case, that is a downward force relative to the ball’s rightward motion. In a freely moving football, this force would curve its trajectory to the side. (GIF credit: SkunkBear/NPR; original video: NASA Ames; via skunkbear)
Richard Feynman discusses why there is a difference between the past and the future, in this clip from his legendary 1964 lecture series at Cornell: The Character of Physical Law.
It’s well worth taking 45 minutes out of your day to hear Dr. F explain why the workings of nature unfold in one direction. You see, while we innately know that the future is different from the past, and so much of our conscious experience is built around the fundamental just-so-ness of time moving forward, the equations of physics describing phenomena from gravity to friction can be run in either direction without breaking the rules. Yet irreversibility is what we observe.
That’s where entropy and probability come into play. When we take into account complex systems, like the jiggles and wiggles of the uncountable atoms that make up our bodies and this chair and my coffee and our world and even out to the scale of the universe itself, there is simply a greater chance that things will become more disordered than less. It’s not that the universe can’t run in reverse, it’s just that there are so many other ways for it not to.
Or as Feynman says, nature is irreversible because of “the general accidents of life”.
This seven-part series, which Open Culture has assembled in its entirety, captures the physicist in his prime, one year before he won the Nobel Prize and became a household name. Feynman was seemingly born for the scientific stage. He had this uncanny ability to weave profound observations of the universe’s inner workings with off-the-cuff (and often brash) humor. James Gleick wrote of Feynman’s unique style and skill:
He had a mystique that came in part from sheer pragmatic brilliance–in any group of scientists he could create a dramatic impression by slashing his way through a difficult problem–and in part, too, from his personal style–rough-hewn, American, seemingly uncultivated.
This clip was a huge influence on my recent video Why Does Time Exist? Although my take scarcely measures up to Dr. Feynman, you can watch below: