# Science over the globe, part 2

We continue to recall the unusual and beautiful science-fiction videos "Science over the Globe" ( Science off the Sphere ) by astronaut Donald Pettit.

First part

## Episode 8. Swill

Curious effects begin if we replace the water with a non-Newtonian fluid on the laptop speakers (in this case, the starch solution of the pancake dough consistency). In a non-Newtonian fluid, the viscosity depends on the velocity gradient. Corn starch increases its viscosity during shear, so on vibrating dynamics part of the solution will behave like a solid and will tend to fly away. But after moving away from the source of vibration, the solution will again become fluid and will 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 speaker, as if it were something alive.

Question: Corn starch increases shear viscosity. And what will happen if you use a shear viscosity reducing agent instead, for example, ketchup?

A shear viscosity reducing agent will tend to scatter rather than pile up. At the edges of the column, where vibrations end, such a substance will gather and form a ring.

## Episode 9. Electrodiggeridu

Didgeridoo - the folk wind instrument of the Australian aborigines. The eucalyptus pipe with a length of one to three meters did not fit into the Soyuz, so Donald had to experiment. On the ISS there were pipes for a vacuum cleaner, which, it turns out, make a very similar sound (compare with the original instrument ). Just a pipe, a pipe with a nozzle or two connected pipes sound differently. And in order to delight not only the ear, but also the sight, Don Pettit and Daniel Burbank live recorded the sound on the microphone and fed it to the speakers. The resulting experimental tool mixes science, culture, physics, and cleaning items.

Question: Why does the amount of water on the columns affect how often splashes fly out?

The more water, the larger its surface area. The speakers act with force on the hemisphere of water, increasing the pressure inside. Pressure is a 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 it is that at some point it will overcome the force of surface tension, and a new drop will fly away.

## Episode 10. Legovatty

On the ISS there is a LEGO. Even more fun, there is even an official NASA manual with examples of useful educational designs. But, since the idea of ​​Lego is in the works, Donald solemnly discards the instructions and collects the Van de Graaff generator with a Leyden jar . These ancient devices (the Leyden bank will soon be 275 years old, and the generator is 90) look a bit strange on the ISS, but nevertheless, they work fine. The Van de Graaff generator allows you to get a very high voltage (with a very small current), and the Leyden bank is a simple capacitor. As a result of their work, distinctly audible electrical discharges are obtained. And at the end of the video Donald, rubbing foam about different materials, tells him a positive or negative charge. As a result, a charged piece of foam is attracted to an oppositely charged generator, or repelled by a similarly charged one.

Question: Why is a household outlet in which a voltage of 220 volts is life threatening, but Donald can safely touch a leyden jar with a voltage of 30 thousand volts?

Kills current, not voltage. Voltage only determines the way in which current flows (it follows that with a very small voltage, even a large current will not flow through the human body and will not be dangerous - approx. Trans). A Leyden bank can have a voltage of 30,000 volts, but has a very small charge, which means that the current will be very small. The Van de Graaff generator generates a very small current, and therefore it does not make sense to use it in a power plant. And in the outlet can be a very large current, which makes it deadly.

## Episode 11. We burst balls in zero gravity

As a child, some of you filled the balls with water and threw them from a height (or someone). It is good to be an astronaut - you can burst balls with water in space and call it a popular science program. Seriously, after the ball burst, interesting things happen to the water. First of all, there are two shock waves that form a shape similar to a cylinder. Then the water in its shape becomes like a potato and, if it were given time to calm down, in the end it would become a sphere.

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

When the ball bursts, the water is in the form of a potato, and an impulse comes in from the ends. Most likely because the ball is thicker at the ends. Then the water is flattened into the cylinder, and the surface tension forces keep it from splitting completely. At this moment, the surface tension from the sides compresses the water, making it potato-shaped, and restarts the cycle. Over time, the water calms down and becomes a sphere.

## Episode 12. Spring Theory

In zero gravity, the spring will overcome only the force of friction on the air (and it is small), and the nut suspended between the springs will fluctuate very steadily. The period of oscillation depends on the mass, and space scales operate on this principle - the astronaut takes the place of a nut on a powerful spring. But to simulate gravity with a spring, having hooked it to the pendulum, was not particularly successful - the harmonic oscillator turned out more likely, because the oscillation period will depend on the mass (in the physical and mathematical pendulums the mass of the load is not important).

Question: Twenty oscillations make the first nut in 21.26 seconds, the second - 10.7 seconds, and the third - 14.2 seconds. What is the mass of nuts relative to each other?

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: In the task, only the nut mass changes. It is proportional to 1 / (f) ^ 2. Knowing the frequency, we obtain the mass ratio.

## Episode 13. Astroduva

The simplest action “to blow water” in weightlessness gives rise to a complex interaction of surface and internal waves, which is also so beautiful that almost half of the video we hear Donald's enthusiasm. And if you sprinkle water instead of air, then its greater impulse may even generate a large bubble inside the water. At the same time, thanks to capillary forces, the water bubble is held in the frame, sticking to the wire. And then, “be it a parallelepiped,” the experiment will be drunk, for the pathos of saving resources.

Question: How does the volume of water affect the response of the water sphere to the waves?

With an increase in the water sphere, its mass increases, and the sphere will have greater inertia. An increasing part of the impulse from the air will pass into the creation of waves, and less and less into motion of the sphere. Oscillations of a larger body will cause more water to roll back than a smaller body. Also, the surface oscillations take more time to reach the opposite end of the sphere.

## Episode 14. Yo-yo

Even in a toy like yo-yo, if you wish, you can find a lot of physics, especially in weightlessness. Donald shows tricks with yo-yo, inventing names for them (who first came up with the trick, he calls him, and, in weightlessness, the yo-yo, it seems, has not yet taken it). There is a rather funny long Donald passage in the video: “Know the physics of your toys. If you understand how it works, you can participate in great conversations. If you're a guy, you can impress girls with a story about physics. Of course, some girls will not be interested in this, but you should not communicate with such in any case. On the contrary (for girls) also works. And you can find a good job and play with pleasure in your free time. ”

Question: How is the cable maneuver trick ( 0:50 ) used in real satellites?