What dust is made of, is toothpaste good for teeth, is cow's milk really good for children, and other questions from our readers.
What is the main dust in our apartments, and what exactly is it harmful?
Veronica M., Cheboksary
The lion's share of house dust is made up of small particles of organic origin - first of all, the remnants of dying cells of the epidermis of our own skin. It also contains scraps of tissue and paper fibers. Other components of house dust enter the room with the outside air and can be quite diverse: pollen from plants, particles of soot from car exhaust, etc. House dust is a habitat for the smallest mites, rather harmless saprotrophs that feed on its particles. These spiders do not tolerate known diseases and do not spoil food, however - like the dust itself - they can cause the development of allergies, including in a very unpleasant form of asthmatic diseases.
Which city in the world is considered the largest in terms of population today, and which ones are in second and third places?
Irina Vorontsova, Sochi
Many of the largest metropolitan areas do not have clear boundaries that would separate them from satellite towns and suburbs. Therefore, in modern urban studies, it is customary to talk about urban agglomerations that unite the megalopolis itself and its immediate surroundings. In the list of the most populated agglomerations, the leader is Tokyo with almost 35 million inhabitants. Two Chinese monsters are stepping on his heels - Guangzhou (32.3 million) and Shanghai (29.4 million). In general, the top ten largest cities are entirely Asian "tigers", with the exception of the 22 millionth Mexico City, which closes this row. The largest agglomeration of Russia - Moscow - is still in 16th place: its population is estimated at 16.6 million people. St. Petersburg is in 73rd position, and there are no more in the first hundred of the largest cities of the former USSR.
What are monkeys capable of? They are known to understand speech, but can a monkey be taught to read and write? What else can she do?
Alexander M., Omsk
Some of the great apes - chimpanzees, orangutans, bonobos, and gorillas - are indeed capable of associating specific concepts with specific symbols in a language, but their ability to master a real language with its complex syntax is rather limited. Most often they are compared to the abilities of young children who are just beginning to master speech. The most "genius" primates can accumulate quite an impressive vocabulary of dozens of concepts, but they compile sentences of a maximum of two or three words in length. But in general, the cognitive, cognitive capabilities of our closest relatives are a vast and fascinating topic, worthy of at least a separate article, and we will definitely tell you more about it in more detail. Suffice it to mention that monkeys can master the rudiments of economic thinking, deliberately deceive each other (and people), and even have a sense of humor - albeit quite peculiar.
Is toothpaste so useful for teeth, and what happens if you don't brush your teeth at all?
Arkady Loginov, Novosibirsk
If you don't brush your teeth at all, you will soon need dentures. The key benefit of this process is the removal of food bits that always remain in cavities and gaps between teeth, in the folds of the gums and cheeks, and serve as a substrate for the nourishment and reproduction of many bacteria, including those that cause tooth decay. In addition, cleansing removes sugar - ideal nourishment for these same harmful microbes.In addition, modern tooth-cleaning pastes contain special substances that can have an active antimicrobial effect (for example, triclosan or chlorhexidine) or are simply capable of strengthening enamel (fluoride or xylitol - urea). Treatment-and-prophylactic pastes can reduce the sensitivity of tooth enamel, weaken inflammation, absorb unpleasant odors … Brush your teeth more often: toothpaste is really useful.
What are the modern concepts of artificial intelligence based on: only on intelligence, or can human feelings theoretically be programmed as well?
Anatoly Sokolov, Minsk
It all depends on what is meant by reason, intellect and feelings. If we are not talking about a feeling, say, of duty to the Motherland or love for one's neighbor, but about emotions, which are one of the basic functions of our brain, then many modern computer models are trying to include them. For us, feelings (fear, pleasure, etc.) serve as key markers of the significance of information, which determine many of the processes of its processing. Such "simulators of feelings" can serve as an equally important service for computers, ensuring the selectivity of the choice and processing of data.
Is cow's milk really good for babies?
Anna O., Moscow
The question of the usefulness of cow's milk remains controversial, but judging by current trends, its healing power in the past has been greatly exaggerated. To begin with, milk sugar - lactose - is not a very friendly substance for the human body, and the majority of the world's population is still unable to assimilate it. However, this does not apply to the inhabitants of Europe, where the gene for lactase resistance is very widespread. At the same time, cow's milk is extremely rich in easily digestible minerals, primarily calcium useful for bone growth. It contains a lot of magnesium, potassium, sodium, phosphorus, chlorine and sulfur, many trace elements, including zinc and iron. On the other hand, these substances are much more abundant in other healthy foods, such as cabbage. In a word, discussions around milk continue.
How to light a fire without any modern tools - matches, lighters, flammable liquids, etc.?
Sergey B., Sevastopol
For hundreds of thousands of years that a person has been familiar with fire, he has invented a great many ways to breed it - matches and lighters have become only the most modern and fastest. Fire can be obtained by heating fine, flammable tinder (such as wood dust) by rubbing or concentrating sunlight through a lens made of glass or water. Fire is made by passing a weak current through metallized paper-foil, in which cigarettes in a pack are packed. There are countless ways - we can recommend to look at the YouTube video channel of the famous Russian adventurer Grigory Sokolov, who in his videos demonstrates in detail many of the most original ways to get fire in any conditions.
What is the swing of the pendulum based on?
Grigory T., Tomsk region
From the point of view of physics, the swing of a pendulum is a harmonious transition of potential energy into kinetic energy and vice versa. This can be the elastic energy of a compressed spring or a load lifted in the gravity field.