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Sounds with a high frequency, over 20000 Hz is ultrasound. They are very weakly scattered, go like a "ray" and therefore very convenient for location. For this reason, not only bats, but also modern instruments - sonars, use ultrasound for echolocation, especially in water...

Now we talked about how fraction takes its natural shape - spherical. If you remember what was said earlier about weightlessness of the falling body and take in the calculation that at the very beginning of the fall one can neglect the negligible air resistance, then realize that the falling portions of the liquid must also take the form of balls. Indeed, falling rain drops have the shape of balls...

Attach a colored piece of paper to the rim of the cartwheels (or to the bicycle tire) and watch it during movement of the cart (or bicycle). You will notice a strange phenomenon: while the piece of paper is in the lower part of the rolling wheel, it is seen quite clearly; in the upper part it flashes so quickly that you do not have time to see it...

On the inertia in rotational motion the device of original entertainment is based - "the wheel of laughter", which can be seen, for example, in the parks of culture. Visitors here have a chance on themselves to experience the action of inertia...

Crystals are solid substances that have a natural external shape of regular symmetrical polyhedra based on their internal structure, that is, on one of several certain regular arrangements of matter constituents (atoms, molecules, ions). The particles forming this solid matter form a crystal lattice. If the crystals are heated to their melting point, they begin to melt...

A long jump of the master of parachuting, begins at an altitude of about 10 km. Only after flying a significant part of the way, he pulls the ring parachute and the last hundred meters goes down, hovering on his umbrella...