The videos came out as a popular science show, with an interval of a week or two, and at the end of each clip, Don asked the audience a thematic question. Answers under the spoilers, so you can calmly think (there are very difficult questions). Speech in the commercials, of course, is English, but you can read the automatic translation of subtitles, and I previewed the video with comments / explanations.
Episode One . Experiment with knitting needles
On the ISS, you can take a small amount of personal belongings, and knitting needles, most likely, went into space for the first time. But not for knitting, but for experiments with electrostatics. If you rub the spoke, it will become electrically charged. And having an opposite charge a drop of water will be attracted to it, flying around in circles. The force of attraction is subject to the law of inverse squares, and the drop will move as a small satellite (gravitational forces also obey this law). With one exception, the source of gravity in nature can be represented by a material point (stars, planets and other heavy objects have a spherical shape), but here the force field is cylindrical, and the droplet moves not in the plane of the orbit, but in the three-dimensional region. The droplet motion can also be compared to the behavior of charged particles of the solar wind falling into the Earth's magnetic field.
At the end of the video, Dr.. Pettit places nylon spokes near the syringe, which injects water near the Teflon knitting needle. Why should Don need a nylon needle, and why should the second spoke be Teflon?
Teflon takes electrons from those materials that rub it, acquiring a negative charge. Nylon, on the contrary, gives away electrons when it is rubbed, and acquires a positive charge. Drops of water, flying around the nylon knitting needle, acquire a small positive charge from it. Different charges are attracted, and water drops begin to tend to the negatively charged spokes.
The second episode. Bistronavta
This is not said in the video, but a cup for drinking in weightlessness invented the same Don Pettit back in 2008 in his previous flight. Usually astronauts and astronauts drink from plastic bags with tubes. They can be used to make powdered drinks, make tea or coffee. But if we make a special cup with an angle on one side, the capillary effect will cause the liquid to rise in this place. And from the cup you can sip the liquid. In the video, astronauts and astronauts for the first time clink glasses in zero-gravity conditions. The design of Pettit is quite simple, then developed beautiful curly cups, but the effect they use is the same. The same capillary effect is used in "serious" missile construction – such angles keep liquid fuel near the neck of the tanks, so that when starting up in the engines did not hit the bubble of gas boost. Only then, when the engine starts to gain traction, liquid fuel will be below under its own weight.
Question: Why can not we use a regular cup in weightlessness?
Because of the wetting forces, water will tend to spread over the walls. A small indignation like sipping can tear water off the surface. If the surface tension forces can not hold water, it will fly away everywhere. In the space circle, the liquid remains at the walls, and the capillary forces do not allow water to detach from them when you drink.
Episode 3. Physics of thin films
On Earth, you can get a film of water only if you seriously reduce its surface tension. This experiment is often involuntarily put by children, playing with soap bubbles. When there is gravity, you can not get a film of distilled water, but in zero gravity, amazing effects appear – drops of water that have been thrown out of the syringe can enter the film, reflect from it, or even fly right through. And if we take a soldering iron and create a temperature gradient, the Marangoni effect will appear in the film – the displacement of the substance due to the difference in the surface tension. In this case, you can get the movement in the opposite direction. If the film of water is convex, that is thicker in the center, then the convection will be sideways, and if the film is concave, that is, thinner in the center than at the edges, then convection will be directed to the center
Question: Why does the shape of the water film determine the direction of the Marangoni effect?
Heating Reduces the surface tension, and water begins to move away from the heat source. But in which direction will it go? Water heats up faster where its layer is thinner, so it tends to go along a more subtle path. In the case of a convex film, these are the edges, in the case of a concave – the center.
Episode 4. Vortices and lenses
We continue experiments with thin films. In them, the viscous forces are relatively weak, so if you twist such a film, pre-colored, it will be seen that it is able to rotate by minutes. A drop of dye, hitting the film, forms a mushroom shape, in fact, which is a longitudinal section of the vortex ring. The same effect can be obtained if the blow through the tube on the film. Well, finally, the water film works like a lens – convex will be collecting (positive), and concave – dissipative (negative). Flat film will neither increase nor decrease the image.
Question: How does viscosity affect the Vortex?
The greater the viscosity, the less the vortex, because, the greater the viscosity, the greater the attraction of the molecules, therefore, for example, in vortices will be less than in Water
Episode 5. Entertainment with antipusters
Due to the forces of surface tension in weightlessness, one can make a bubble from the air inside the bubble from the water, and with a certain luck for a while – a bubble from the air inside the bubble from the water flying inside the air bubble inside the water bubble. And all this is still rotating.