Why?

2023-05-21 14:00:12 WHY do people like the smell after it rains?

The smell of rain has a term: petrichor.

When rain falls on the ground, water enters microcracks and pores. The air in them forms bubbles on the wet surface, which, when they burst, release many microdroplets into the air.

These tiny particles, containing oils of plant origin, are picked up by air currents and are spread around, creating that unique and beloved by many fragrance.

For the same reason, by the way, when it rains, a huge number of soil bacteria end up in the air. So when you say you smell wet soil, it is actually a molecule produced by a certain type of bacteria. This molecule, geosmin, is created by Streptomyces bacteria. Открыть/Комментировать

2023-05-20 21:00:06 WHY are there no tides in the Black Sea?

In the Black Sea, tides occur independently of the World Ocean, as tidal waves do not pass through the narrow straits of the Bosporus and the Dardanelles. Tidal forces are related to the different force of lunar gravity acting on parts of any water area not equally distant from the Moon.

The Black Sea water area is much smaller in cross-section than the entire Earth with the World Ocean. Hence, the tidal forces are just as small here.

The water in the sea is actually just rocking, as in a basin: the amplitude of the tide on the east coast, in Batumi, reaches 13 cm, on the west, in Burgas, - 10-11 cm, and on the southern coast of Crimea sea level rise is no more than 1 cm. Открыть/Комментировать

2023-05-20 14:00:08 WHY does the water jet narrow toward the bottom?

Slow and calm - laminar, as physicists say - the jet from a circular faucet first has a cross-section equal to the inner diameter of the pipe. Under the action of gravity, the flow accelerates, and since the flow of water doesn't change, the jet should narrow.

One can take a different look at it. Among two drops, that came out of the pipe with a small time gap, the first one starts accelerating earlier, and its detachment from the second one is constantly growing. Thus, gravity stretches the jet vertically. Since the volume of water between the drops remains the same, the jet is thinning.

At that, it is compressed by surface tension forces, and when the jet becomes quite thin - 2-3 mm - they also crush it into separate drops. Открыть/Комментировать

2023-05-19 21:00:29 WHY is it dangerous for cats and dogs to go extinct?

Many cats and dogs, especially ornamental breeds, are almost incapable of making their own food in the wild. Even urban stray dogs and cats live mostly off people - intentional feeding and food scraps.

Furthermore, even completely feral dogs tend to lose competition to wild dogs like wolves, coyotes, etc. Living in the same territory as them, without human support, willing or unwilling, they quickly become extinct. However, in the absence of wild competitors, some dogs and cats are quite capable of mastering an independent life.

The most famous example is the Australian dingo, the feral descendant of domestic dogs, now the largest predator in the Australian fauna. In Australia, as well as in a number of other places, there are stable populations of feral domestic cats. Открыть/Комментировать

2023-05-19 14:00:42 WHY is maple syrup hard to obtain?

The tradition of maple sap harvesting, borrowed by Canadians from the Indians, took shape in their favorite and annually held in March, the national holiday of the inhabitants of Southern Quebec and Ontario. It is possible to get 20-25 liters of the most valuable sap from one tree only from sugar maple (Acer saccharinum).

These trees, which reach 30 m in height, grow in the south-east of Canada. To collect the sap, an incision is made on the trunk, approximately 20-30 cm above the ground, into which tubes are inserted leading to vessels where the sap, called passoka, flows. To obtain a sweet maple syrup or sugar, which instead of sucrose contains more useful dektrose and trace elements, the juice is thickened by evaporation. It takes 40 liters of juice to make 1 liter of syrup.

Maple syrup is an essential ingredient in many Canadian dishes. It is used in ice cream, soufflés, porridges and even some meat dishes. Открыть/Комментировать

2023-05-18 21:00:33 WHY do persimmons cease to be astringent after freezing?

The astringent taste of persimmons comes from tannins, substances of a phenolic nature. The fruit has enzymes in its tissues capable of hydrolyzing these compounds, which leads to the destruction of the latter. However, tannins and enzymes in the unripe fruit reside in different intracellular structures separated from each other by membranes.

During freezing, ice crystals rupture the membranes, and after defrosting, the tannins are hydrolyzed. Their destruction also occurs as the fruit ripens, so a fully ripe persimmon is not astringent. Открыть/Комментировать

2023-05-18 14:00:42 WHY do people blink?

Studies tell us that the average person blinks once every 2 to 10 seconds. We do this automatically as our eyelids protect our eyes from damage. Sometimes we blink intentionally, using what is called "sign language". As an example, we may blink to get attention, inviting another person to flirt. Sometimes we blink to express surprise, as if to say, "I can't believe my eyes!"

In humans, the inner surface of the upper and lower eyelids, as well as the eyes themselves, are lined with a thin, almost transparent membrane, the conjunctiva. The conjunctiva serves to moisten the surface of the eyes, because they need moisture to move properly. During blinking, the eyelid spreads moisture through the conjunctiva and also directs it to the corners of the eye. Открыть/Комментировать

2023-05-17 21:00:30 WHY does a dozen bear a separate name?

For it has many divisors

A dozen is the smallest number that has six different divisors, four of which are in a row: 1, 2, 3, 4, 6, 12. It is convenient in use, so counting in dozens was used in some monetary systems and in cattle breeding, where derivatives were also used.

Inch dozens are grosses (144) and dozen grosses are masses (1728). We are left with the division of the dial into 12 hours and the word "dozen" from duodecimal counting. Открыть/Комментировать

2023-05-17 14:00:40 WHY is the unknown in mathematics commonly denoted by the letter x?

The Spaniards used this letter to write the Arabic word for "thing”.

The story began in the ninth century in Khorezm in what is now Uzbekistan, where the mathematician Al-Khorezmi laid the foundations of the science of solving equations - algebra.

Its name comes from the Arabic term "al-jabr," which means the transfer of an equation term from the left side to the right side with a change in sign. Открыть/Комментировать

2023-05-16 21:00:31 WHY can't bees fly over mirrors?

In 1963, the Austrian entomologist Herbert Heran and the German behavioral scientist Martin Lindauer noticed something strange about the way honeybees fly through the air. When a group of bees was trained to fly over a lake, they could only fly safely to the other shore if there were waves and ripples on the surface of the water.

At the same time, when the lake was mirror-smooth, the insects suddenly lost their orientation - and even fell into the water. The results of that study confirmed the idea that bees use visual cues to navigate during flight.

In other words, when the surface below the bees is mirrored, the insects assume that the ground below them is much farther away than it really is, and they lower their altitude to the limit. Открыть/Комментировать