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Science on the globe, part 2 / SurprizingFacts

We continue to recall the unusual and beautiful popular science videos "Science off the Sphere" by astronaut Donald Pettit.

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The Episode 8. The Liver

Curious effects begin if on the speakers for the laptop we replace water with non-Newtonian liquid (in this case – starch solution consistency of pancake dough). In a non-Newtonian fluid, the viscosity depends on the velocity gradient. Corn starch increases its shear viscosity, so on the vibrating dynamics part of the solution will behave like a solid and will tend to fly away. But after leaving the source of vibration, the solution will again become a liquid and begin to experience surface tension forces that will tend to drag it back into the speakers. As a result, a complex form appears that will change its appearance and move far enough away from the dynamics, as if something alive. ] Question: Corn starch increases the shear viscosity. And what will happen if we use a shear-reducing substance, for example ketchup, instead of it?

Response

The shear-reducing substance will tend to fly apart rather than gather in a heap. At the edges of the column where the oscillations end, this substance will collect and form a ring.

Episode 9. Electrodeaderid

Didgeridou is a national wind instrument of Australian Aborigines. Eucalyptus pipe length of one to three meters in the "Union" did not fit, so Donald had to experiment. At the ISS, there were pipes for the vacuum cleaner, which, it turns out, produce a very similar sound (compare with the original instrument). Just a pipe, a pipe with a nozzle or two connected pipes sound different. And to delight not only the rumor, but also the vision of Don Pettit and Daniel Burbank, they wrote the sound to the microphone live and handed it to the speakers. The resulting experimental tool mixes science, culture, physics and objects for cleaning.

Question: Why The amount of water on the columns affects how often the sprays fly off?

Response

The more water, the larger the surface area. Dynamics act with a force on the hemisphere of water, increasing the pressure inside. Pressure is the force divided by the area, so in the big drop the same sound will create less pressure than in the small one. And the lower the pressure, the less likely that at some point it will overcome the force of surface tension, and a new drop will fly away.

Episode 10. Legohvats

On the ISS there is LEGO. What is even more fun, there is even an official instruction from NASA with examples of useful educational designs. But, since the idea of ​​lego is in the works, Donald solemnly discards the instruction and collects the generator of Van de Graaf with the Leiden jar. These ancient devices (the Leyden bank will soon be 275 years old, and the generator – 90) look a bit strange on the ISS, but, nevertheless, work fine. The Van de Graaf generator allows obtaining a very high voltage (at very low current), and the Leyden bank is a simple condenser. As a result of their work, distinctly audible electrical discharges are obtained. And at the end of the video Donald, rubbing the foam on various materials, informs him of a positive or negative charge. As a result, a charged piece of foam is attracted to an oppositely charged generator or repulsed from a charged generator.

Question: Why is a household outlet in which the voltage of 220 volts is dangerous to life, but Donald can safely touch the Leyden jar with a voltage of 30,000 volts?

Answer

Killing current, not voltage. Voltage only determines the way the current flows (hence, with very little voltage, even a large current will not flow through the human body and will not be dangerous). The Leiden can have a voltage of 30,000 volts, but it has a very small charge, which means that the current will be very small. The Van de Graaff generator generates very little current, and therefore it makes no sense to use it at the power plant. And in the socket can be a very large current, which makes it deadly.

Episode 11. We shoot balls in weightlessness

As a child, some of you filled the balls with water and threw them from a height (or into someone). It's good to be an astronaut – you can burst balls with water in space and call it a popular science broadcast. Seriously, after the balloon has burst, interesting things happen with the water. First of all, there are two shock waves that form a figure, similar to a cylinder. Then the water becomes more like a potato and if it were given time to calm down, eventually it would become a sphere.

Question: Why does water fluctuate between cylindrical and potato-like forms?

Answer

When the ball bursts, the water is in the form of a potato, and an impulse appears inside with Ends. Most likely because the ends of the ball is thicker. Then the water is flattened into the cylinder, and the forces of surface tension keep it from being completely shattered. At this moment, the surface tension squeezes water from the sides, making it a potato-shaped shape, and starts the cycle anew. Over time, water calms down and becomes a sphere.

Episode 12. The theory of springs

In zero gravity, the spring will overcome only the frictional force of air (and it is small), and the nut suspended between the springs will oscillate very steadily. The period of oscillations depends on the mass, and on this principle the space scales work – the cosmonaut takes the place of the nut on a powerful spring. But to simulate gravity with a spring, hooking it to a pendulum, was not particularly successful – it turned out to be more of a harmonic oscillator, because the period of oscillations will depend on the mass (in physical and mathematical pendulums, the mass of the cargo is not important).

Question: Twenty hesitations the first nut commits in 21.26 seconds, the second – 10, 7 seconds, and the third – 14.2 seconds. What is the weight of the nuts relative to each other?

Answer

The first nut is 3.95 times heavier than the second and 2.24 times heavier than the third. The third is 1.76 times heavier than the second.

Explanation: Only the mass of the nut changes in the task. It is proportional to 1 / (f) ^ 2. Knowing the frequency, we get the mass ratio.

Episode 13. Astrodovs

The simplest action "blowing on water" in zero gravity generates a complex interaction of surface and internal waves, which is also beautiful enough that almost half of the video we hear Donald's delight. And if you sprinkle water instead of air, then its greater impulse can even generate a large bubble inside the water. In this case, thanks to the capillary forces, the water bubble is held in the frame, adhering to the wire. And then, "if it's a parallelepiped," the experiment will drink, for the pathos of saving resources.

Answer:

As the water sphere increases, its mass increases, and the sphere will have a large inertia. All the greater part of the pulse from the air will pass into the creation of waves, and an ever smaller sphere of motion. Oscillations of a larger body will cause a greater rollback of water back than a smaller body. Also, surface vibrations will take more time to reach the opposite end of the sphere

Episode 14. Yo-yo

Even in a toy like yo-yo, if you want, you can find a lot of physics, especially in weightlessness. Donald shows tricks with yo-yo, coming up with names for them (who first invented the trick, he calls it, and in weightlessness, yo-yo does not seem to have been taken yet). In the video there is a rather amusing long passage of Donald: "Know the physics of your toys. If you understand how it works, you can participate in wonderful conversations. If you are a guy, you can impress girls with a story about physics. Of course, some girls will not be interested, but with such in any case, do not talk. On the contrary (for girls) also works. And you can find a good job and play with pleasure in your spare time. "

Question: How does the "maneuver with rope" trick (0:50) be used in real satellites?

Answer

Yo-yo Donald works as a terminal mass in a wire system with momentum transfer. Donald twists a thread (rope), causing centripetal force in yo-yo. Given that the two-body system revolves around the common center of mass, and Donald's hand simulates a satellite, the yo-yo and the hand will experience constant acceleration. Transmission of the pulse will occur if the terminal mass is released, which will lead to a change in the orbit of the satellite.

Illustration for clarity:

 image

Trans. – a similar experiment was carried out with a capsule of "Fotino", which was successfully removed from orbit by a cable.

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