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Case-lesson "The mobile phone means everything to me"
Case-lesson "The mobile phone means everything to me"
nokia 3310 and nokia 6 - photo by REUTERS

Section: Science, Nature and human

The level (grade): 7-8

Subject: Applied science

Objective: To systematize multi-vector knowledge which is used in the design of mobile phone

What kind of information is there waiting for me?

  • How does mobile phone work?
  • Why is it called a cellular mobile communication?
  • Why do some airlines ask passengers to turn off the cell phones?
  • How are physics, chemistry and mathematics involved in the design of the phone?
  • What fundamental and practical knowledge will be useful for me?
  • How to calculate the probability of my phone?
  • How to find a profitable mobile plan?
  • How does the cell phone affect to a human?
10 scans for objects, phenomena and practices:

Today the mobile phone is considered the as device, which no modern person can live without.

It has the tools that we use most often (15-20). There are those which we turn much less (200-300). Looking at this tiny device, it is difficult to imagine how it "holds" hundreds of gigabytes of information. And how the constructors created it?

The phone is not just a piece of life of the individual, but also a marker of progress and innovation. Science and Technology Achievements are reflected in the capabilities of mobile phones. New needs of mobile phone users motivate inventors, researchers, developers in search of modern scientific solutions.

It also promotes knowledge, because finding new information with a modern phone is easier and faster. It inspires businessmen, designers and it dictates fashion. Now few people can live without it. But it is quite a diffrent thing - how to choose your phone and enjoy all of its features and applications?


Your mobile phone is based primarily on the radio. Principles of radio communications are the following. Variable high frequency electric current, which is created in the antenna transmitter, causes the space around the antenna high frequency electromagnetic waves. When the waves reach the receiver antenna, they induce in it an alternating current of the same frequency at which the transmitter operates.

To deliver high sound vibrations alter or modulate the electrical oscillations using low frequency (audio frequency). This method is called amplitude modulation.

At the receiver with modulated high frequency vibrations produce low-frequency vibrations. This conversion process is called signal detection. The resulting detection signal corresponds to the audio signal, acting on microphone transmitters.

That is, we have the string "sound vibrations - electromagnetic waves - sound waves."


The main elements of the network are handsets and base stations. The antenna base station is divided into several sectors, each of which is directed at its side.


Mobile telephony is a type of modern mobile radio. Its peculiarity is that the entire coverage area is divided by the coverage of individual base stations (BSS). In a perfect flat surface without buildings covering from one station is a circle. But these overlapping circles have formed hexagons - cells. That's why mobile phones are also called cellular.

We do not even notice the work which our mobile is "busy" with when we use it or leave it pending calls. When switched on the phone listening airwaves, seeking alarm base station. Finding the station, the phone sends to it a unique identification code. The station and the phone constantly in contact, communicate. Communication can be both digital and analog. The range of such station is 35 km. The phone can measure the signal strength from 32 stations simultaneously, switching to those from which the signal is stronger.

Operators have agreed among themselves, as subscriber out of range of your network can switch to another. So, it is roaming works.

Mobile (cell) phone works by electromagnetic waves. Electromagnetic wave propagation is the process of electromagnetic interaction in space as variables connected by electric and magnetic fields. Its most important characteristics are the frequency and length. Frequency characterizes not only separate channel, but the entire network. The wave vibrations propagating through space points towards "advancement" wave: the same point in space, moving, and create a wave. This movement in physics is called forced oscillations.

An important feature of the network is the frequency and wave vector.

Depending on the frequency the electromagnetic waves belong to one of the spectral ranges.

Waves in various different bands interact with physical bodies. Waves with greatest frequency are radioactive radiation with a frequency of up to tens of nanometers - waves used for radiography, with a length of hundreds of nanometers - are ultraviolet radiation. Visible light falls in the range of 400 to 700 nm. Millimeter and centimeter ranges - are infrared waves. Longer wavelength belongs to radio waves.


Consequently, electromagnetic waves with the lowest frequency (or the largest wavelength) belong to the radio. Radio used to transmit signals on distance via radio, television, mobile phones. On the radio front works thed radar. It is divided into radio meter, decimeter, centimeter, millimeter, depending on the length of electromagnetic waves.


Why do some airlines ask to turn off the phones during taking off and landing?

There is a probability, although extremely small, that frequency of the phone and appliances plane coincides.

In fact, in modern airplanes devices work on other frequencies. Therefore, not all airlines impose such a requirement to passengers.

For aircraft operating frequency range is 90-150 Hz. Including the piloting purposes of the navigation devices. For some devices used beacons airports operating frequencies are 329-335 MHz frequency range. The frequency is the same number of standard GSM 1-2 GHz with standard UMTS 2-4 GHz. For a 3G frequency is about 2 GHz.

Also, all mobile phones have mode "on the plane." Mode " on the plane " is a setting that allows you to quickly turn off all wireless communication means. By means of wireless communication includes Wi Fi, mobile broadband, Bluetooth, GPS or GNSS, at a short distance radio communication (NFC) and more.

Are smartphones afraid of sun?

Another type of physical phenomena, which is associated with your mobile phone is light. First of all, it is about the screens of our phones. Most modern phones have touch screens. The development of sensor technology is in two directions: resistive sensors (such that you can manage any objects) and capacitive sensors (those that react only to objects that conduct electricity). Latest let you control some areas of the screen simultaneously - this is the multitouch.

The capacitive touch screen is a glass panel covered with a transparent resistive material (commonly used the alloy of indium oxide and tin oxide). The electrodes are located on the corners of the screen, served on the conductive layer a small AC voltage (equal for all corners). When you touch the screen with your finger or other leading object a leakage current appears. Thus, the closer finger is to the electrode, the less is the resistance of the screen. This means that the current strength is greater. The current in all four corners of registered sensors and transmitted to the controller calculates the coordinates of the point of contact.


But such capacitive technology is a significant drawback - it is a complicated control in cold. Resistive technology does not have this disadvantage.

The sun rays affect the screen: the higher the allowable brightness of the screen, the easier it is to read information from a sunny day.

Light is falling on the screen (the surface) at a certain angle. Part of this light is absorbed, some is reflected. The percentage of absorbed (or reflected radiation) will depend on the color of the surface. That is, each pixel of the screen will reflect and absorb light in its own proportions depending on the color.


Thus, for the user is important phone screen illumination.

Illumination is a physical quantity equal to the luminous flux that falls on the illuminated surface unit ("lux" is its unit of measurement):


where F - luminous flux; S - area that is illuminated (in square meters).

For this you can calculate the ratio of luminous flux that is directed to the mobile screen in different conditions. Illumination in different conditions is:


That is, if my phone screen area is 0,008 square meters, then it will be under different conditions fall a luminous flux:


So not only the brightness of the screen is important, but the illumination while using it.


What is the illumination of the screen of your phone in this moment of time? What it will be at night? Compare the calculations.

Why my phone is running out so fast? Which phone is "durable"? Can chemistry help find a "long-playing" battery?

Yes, because the main principle of the battery is receiving electrical current by chemical reactions. And on what elements of the periodic system will be used depends on the length of battery "life" to discharge.

Important parameters for assessing batteries are:

• High density electrical;

• The number of cycles "charge - discharge";

• Optimal size.

Types of batteries which are used in mobile phones (lithium is the most widespread among them):


Lithium-ion batteries have a high electric density, large number of cycles "charge-discharge". This battery consists of electrodes (anode and cathode) separated by a porous separator that is permeated electrolyte. Packet electrodes placed in a sealed enclosure.

Another type of battery is Torah. This is a new generation of rechargeable batteries, which now "takes a step" from research laboratories to real life.

Thorium (Th) is a metal with weak radioactivity. It does not bring damage to life and health (exception is getting directly into the blood). It is not included in biospheric processes as a factor which is not harmful to the environment. Thorium is used for concept cars (representational new generation of car models) and Innovation "advanced" battery models (including mobile phones).

Future thorium battery depends on how they are in operation soon.

Nickel-cadmium has little energy for large size of the battery. They are found only in old phones.

Lithium-polymer batteries are the most technological. They have a minimum thickness used for ultra-thin phones. Also, these batteries are installed in electric vehicles.

In general, the electrochemical reactions occurring in the battery can be represented as follows. Imagine a metal plate that is immersed in water. Under the influence of polar water molecules metal ions detached from the plate and hydrated pass into the liquid phase. The liquid phase thus receives a positive charge, and the metal plate has an excess of electrons. The longer the process is, the greater the charge has both plate and liquid phase. Will have the process on the scheme:


where Me(solution) - metal in the solid phase;

Me(solution)n+ - in a rare phase in the form of ions to the discharge n+

(if removed two electrons - charge 2+, 3 electrons - 3+ etc.);

ne - removed electrons (2,3 etc.)


For summer, for example, the reaction scheme will look like:



If the environment changes, the balance moves (principle of Le Chatelier). Instead of water a solution of salts or special gel or special porous materials - membranes can be used. They have a selective ability - pass only ions that we need for battery. In summarizing the external current electrochemical process will have two parts: the first is on the anode, the second is on the cathode.

At the cathode metal ions are reduced to metal in a solid (metallic form):

Me(solution)n+= +ne = Me(solid)


For lithium cathode pass this process:

Li+(solution) + e = Li (solid)


At the anode goes further oxidation of metal ions:

Me(solution)n+ - хe = Me(solution)(n+x)+

where xe - «removed» by oxidation of x electrons

Me(solution) (n+x)+ - the metal in the oxidized form received a new charge (n+x)

Given the possible degree of oxidation for Li (1), this process will go simply by increasing the amount of oxidized ions.


To these basic chemical processes can be reduced most modern battery operations.

Why soes phone run out?

For this we use the explanation by Daniel Abraham, a scientist from Arahonnsk National Laboratory, which investigates lithium-ion batteries. He draws an analogy between the battery and a bucket with water. Charge is filling buckets. Extent bucket is battery capacity, the speed with which it can fill its power. But time, the effect of temperature and other factors form a "hole" in the bucket. By analogy with a bucket - "water leaks." Lithium ions are removed, link. They lose the ability to move between the electrodes. Over time, the number of bound ions is increasing. The phone that charged every few days, begun charging each day. After some amount of time the ion battery will not contain any useful charge - "bucket stops to hold water."

Why heat is harmful to my phone? When the temperature of electrolytes decompose faster, and the rate of adverse reactions, which bind lithium, is also increasing. So the battery is discharged faster, and another cycle of "charge-discharge" can be removed from the life of the phone.


Find out what type of battery your phone and the phones of parents or friends have. Follow how often they need charging. Consider how this can be explained?

Modern mobile phone is a child of many advanced technologies. Large companies with modern laboratories and brilliant teams of specialists are working on its improvement.

Areas of improvement are different from modern "e-filling" for convenient and interesting design, from ultramodern software to new special body material or screen.

Let's try to understand this area.

First direction is information technology.

Question: "What is better, iPhone or smartphone Android? » akin to heated debates. Who are the companies that broke forward in convenience and innovation? Typically, this option leads to a choice when buying.

So, the first facet - the technologies incorporated in the operating system. The main parameter estimates such technology - simplicity and individual settings. Another facet is the ability to support other devices compatible with them. An important focus is the development of "user-friendly interface."

For example Android supports Flash, which is used in many sites. In addition, the source code is open (it is available for all programmers) that allows developers to use it to create applications.


Another important facet in the development of information technology is to synchronize with other devices. It can be an impact not only for technical creativity. For example, the group «Brunnettes Shoot Blondes» from Krivoy Rog removed the clip using 14 synchronized gadgets. Currently clip to YouTube receives more than 8 million reviews.

Recently, 3G technologies are on everybody`s hearing. This term has become not just fashionable, it is to some extent seen as a synonym for the word "development" and "progress." In what is the essence of this technology? 3G is a term used to describe the new generation of mobile services. Literally it means "third generation." It is a set of standards and protocols provided by the companies - operators and used by subscribers. The list of standards and protocols approved by the International Telecommunication Union, and called IMT-2000. It is based on a system of UMTS (universal mobile telecommunications system), which can reach speeds of 42 Mbit / s.

This channel allows multimedia services "on the fly", to "Stream" - live broadcast events. The main key to implementing 3G is appropriate allocation of radio frequencies. 3G era is steadily moving through the world.

There is a modern myth that smartphone cameras have replaced conventional cameras. Technology development is on the one hand in the fight for megapixels, on the other hand - for the use of devices such as flash auto-focus or phone. Modern smartphones use technology that allows even FullHD.

The camera can also be used to scan and object recognition. A striking example of fashion is QR-codes. They give the ability to "read" coded information about the product, facility service.

Example of QR-Code

QR-Codes cameras are designed specifically for smartphones. Three squares at the corners of the code make it possible to normalize the size and orientation, the angle at which the sensor is located relative to the surface of the image. QR-codes can be seen not only on goods and advertising banners, but also on informative boards for tourists (near monuments or art-objects).

Mobile Phone absorbs the technological achievements of modernity. But it encourages development. For example, the development of GIS technology allowed using them for navigation in mobile phones. But most mobile phones had "grow" in the technical and information plan for such possibilities.


Find out which was the first phone of your parents. How is it different from yours? Think about what opportunities you would like to see in your phone and make a "task" for phones developers.

Probability theory and study at school and at university. From simple tasks acquaint students in 5th grade. There is an interesting question: can we assess the probability of failure of a mobile phone?

This is a difficult question to answer is influenced by many factors. But we can use snippets algorithm used to evaluate the reliability of large ATE (automatic telephone exchanges). Although our version would be a much simpler form.

To start, let`s consider on some terms:

Efficiency - something the state in which it performs its job effectively (normally a working phone).

Disclaimer - an event that causes abnormal function (broken casing, screen, filled with sticky juice "caught" the virus from the network, etc.)

Failure - thing that is self-removing (we usually tell about “the phone suddently stopped working and then started again after a while»).


Probability of failure - the likelihood that the phone fails over time:

P = n / No

n - Number of elements that were denied for some time;

No - The number of elements in the question.

Then the probability of trouble-free operation will be:

P = 1 - n / No.

That is one we have received eternal ideal phone that never breaks.

I will consider the time of last year. Telephone for myself conditionally is divided into the following elements: Battery (why it is running we reviewed in Chemistry) screen (the best technology); software, e-filling and casing. Only 5 elements.

Then count only rejections but not failure. Last year the screen was crushed for one time and one time the old battery was replaced. Only 2 failures. So we get:

P = 1 - n / No = 1 - 2/5 = 1 - 0.4 = 0.6 or 60%.

So my phone will work flawlessly in 60% of cases. And yours?


Calculate the probability of your phone.

The modern world criated an aphorism: "If you want to hate a melody, put it in alarm ringtone". We wake up at the sound of mobile phone, read news, weather, communicate in social networks and chats, take pictures and shoot video. All this from a mobile.

From the usual "dialer" it rose to a mobile phone gadget that can replace the camera, computer and many more.

Very often the mobile phone is used to search for information. Search strategy depends on what information you want to find. If you already know what kind of information you need, you have to use Internet resources prospectus.


Just another case, if you know "what it takes", but did not know "where it can be." In this case, the key should be to solve the problem correctly formulated request for a search engine (Google, Rambler, Bing, etc.).

It is important to focus not only on itself "intended finding" but those phrases, words, that it can "accompany" (keyword search). You will have a "sentence". For example, we will seek trains that pass through Lviv. The phrase would have to look "all trains that pass through Lviv". But the search engine will look for just such a set of words and the information that could be needed will be "bypassed" by the system. Therefore, the next step should throw all the "words-parasites" that have key roles to search. This is an example of this - "passing through".  Correcting the phrase into 'schedule trains Lviv ", we’ll get exactly what we were looking for.

Sometimes, on the contrary, it was necessary to find information on a specific phrase. For example - a poem. Then you can enter it on line or some famous words and use quotes "". Quotes are operator "exact match". For example, the poem "Roses are red and violets are blue…" will lead us right to the desired text.

There is an operator of international obligatory presence of the words "+". Or an operator of international obligatory absence of the word "-". For example, "All computer magazines + Chip" (if we want to see this magazine in search results).

You can search on even particle keyword using * or ? . They represent a part of the word random.

What if you need to find out whether the information is reliable? Then, first of all, look at what you are dealing, or the fact of its assessment. The next step is to search for similar information from different sources and compare it. This implies important criteria of reliability of information - "coherence".

Check the unique information (exclusivity) using special sites. For example: Copyscap, Advego Plagiatus.


The phone is not only a tool of voice communication. Thanks to the mobile Internet, we can get on with it in social networks. Most of them have a mobile version, which is more convenient for perception in the phone.

There are analogues of Skype, adapted to the peculiarities of using mobile phone. An example is application Viber. It enables communication between users working on the computer (tablet, laptop, etc.) and the owner. Contacts in Viber can be added as a phone number. It supports voice and text communication.

There are specially designed for mobile applications players (music or video player). Depending on the format of the movie should use a variety of them.

A separate chapter in the development of relations "phone - internet" is mobile game. Some of them have become a cult; have created a niche in the entertainment industry. There is a vivid example where mobile game has moved into real life - Angry Birds. There are both amusement parks created based games (like Angry Birds park in Finland), so the individual attractions.

The cult game Angry Birds

Amusement Park

Mobile Internet can not only use other people's sites, but also to put their own content.

You can upload photos, video, process them online.

Ordinary SMS can be used with e-mail. Finally, there are special mobile versions of e-mail.


Mobile phones and the Internet are closely linked. The main thing is to use a symbiosis with benefit and pleasure.


Explore what sites do you visit most often on the phone, what applications do you use most often? Consider why.

Mobile Phone is in all spheres of human activity. And business is not an exception: the production of mobile phones, software development, providing radio frequencies, providing service or telecommunications services, design, advertising, logistics, sales.

Large companies - manufacturers compete by trying to sell the maximum number of items - phones or phone accessories. Competing companies - operators are trying to give the most attractive tariff and attract maximum number of customers. With the competition between some of them can be seen both in the series interesting: who will pass?


An important issue for the owner of the phone is the rate - how much to pay for calls, SMS and mobile inernet. The formation rate impact: the value of the network, the cost of calls within the network and to numbers of other operators, Internet speed, the cost of calls to regular phones, the cost of SMS.



Choosing a tariff should consider what exactly you use most: SMS, MMS mobile Internet as your "Contacts" use the services of the same operator.


Find out more about existing tariffs and choose the one that suits you. What are the arguments of the choice? What tarif do you use now and why?

Mobile phones have become an essential means of communication between people.

Try to look around you and you will notice how many people are at the moment talking on a cell phone.

But how did we live without mobile, how communicated with others? The answer is simple: we communicated with others in the same way, but in live. And it is because we use mobile not always when it is necessary but just because we can. Now, to talk with friends who live on the floor below, it is not necessary to go down, we need only to dial the familiar number or "knock" to them in Skype, Viber...


Mobile Phone is person’s assistant in many situations when you need talk to someone fast. The possibility of rapid communication not only speeds up the search for information and decision-making by man. The string "Task" - "Information" - "Resolution" is passed now much faster. Simple everyday example: you decide whether you need a sports jacket tomorrow. Today for some reason you were not in school. Tomorrow – physical training. First, watch the weather (through telephone applications). You can then call classmates (here is mobile again!), found if physical education classes are planned outdoors. Knowing weather forecast and where the lesson will take place, the solution becomes obvious.
Widespread received photos or capture "selfie." This trend has a positive effect: people can explore their facial expressions (and it is better to learn that it is important for public appearances), find new features "open" themselves or friends in the world from a new angle, "try on" the role or behavior model. Sent selfie bring you "closer" to those who are far away, uplifting the mood.


The degree of mastery of a certain type of person’s information is evident in its language. How properly and adequately the concept is used such person has this information. Some are not entirely correct use the device names - modern means of communication. That's a "crib" for this case:


Mobile phone has artificial intelligence. For mobile phone (the operating system) is able to make decisions, program or application "hung" and it should close by to offer contextual advertising ...


Examples of artificial intelligence - Android and iOS. Both operating systems have the following features of Artificial Intelligence:

1) The ability to choose and make the best decisions on the basis of earlier experiences and analysis of external influences (Any relies on intelligence activities).

2) The most important difference between genuine software artificial intelligence of simple applications is the ability to "think" with images. (With imaginative thinking today became available technologies such as compression and coding of information, processing of biometric images to optimize color gamut, like search, analysis of the meaning of images, automatic cataloging information, recognition algorithms and classification of images.)

Artificial Intelligence - promising area of technological development.


For example, Google plans to create artificial intelligence that would allow improved sorting information to search requests. Such development should be completed by 2029. The result should be an intelligent search engine that has emotional intelligence. It has to understand human emotions.

Japanese National Institute of Information develops artificial intelligence system, called Todai Robot. It must seize this level that in 2021 successfully pass the entrance exams in the leading universities of the country.


Explore what exactly signs of artificial intelligence has your phone got?

It would seem that sharing between a mobile phone and cinema, Hollywood stars? In addition, of course, the phone in the frame - a familiar feature of our time, which is no longer a surprise or admiration?

But this relationship exists. His name is Hedy Lamarr.


Hedy Lamarr is an Austrian-American actress and inventor.

Mathematically gifted, she and composer George Anteyl invented a method of spread-spectrum communications and frequency hopping adjustment required for wireless connection of the pre-computer era to the present day.

She played in 30 films, earned 30 million dollars, and has got a star on the Walk of Fame.

But in addition to movies, Hedy Lamarr engaged in science. Back in 1942, she patented a system to manage at a distance of torpedoes. Now this technology is used in the "peace line" - in our mobile networks. The value of technology "frequency jumping" was evaluated only over the years.

Actress birthday - November 9 –is the Day of the inventor named in German-speaking countries. Without Lamarr invention there would be no flying military satellites cellular phone standard GSM would not work, there would be no Bluetooth headset.


A new model is not even on sale, but at a previous advertising company as it begins high demand. Mobile phones become unfashionable, even without having technically obsolete. Importantly phone is "Status" attribute, reflecting all changes of life.

Successful advertising campaigns encourage fashionistas to "upgrade" the phone to the long-awaited news. Even in spite of their price that "animates" the market of consumer loans, many people want a new phone now, and pay for it "sometimes and gradually."

For example queue for iPhone 6S lined up for 4 days before the start of sales:

The queue for the iPhone 6S in Germany

Advertising companies are promoting not only the phone itself, but also related products (mobile accessories): headsets, headphones, blankets or chains, for example. In this case, designers offer huge scope for creativity: successful decision, trendy finishes, using the popular image and we have “ideal" trendy goods. In this case the appeal is reinforced: fashion phone in a cover from a reputable manufacturer of fashionable image. Some advertising campaigns oriented to specific categories of customers: women, girls, teenagers, etc.

Modern phone-bracelet.

Fluidity fashion drives technology contributes to their development. But it is important not to do sensible approach to fashion: buying something new for status only the sake, not for opportunities, it is not good life position.
Although for many people the question of status is also very important, as they pay attention to brands. Technology allows brand promotion to become such a commodity that is easily learned. This allows, in turn, receive additional income from the so-called "intangible assets", which include trademarks, brands, and patents. As a result: the brand product has advantages for both producer and consumer.
Such goods like cars, watches and smartphones, called threevector as they meet just three consumer needs. For example, the car can be seen as a convenient vehicle, a professional agent and a subject of prestige.

The same situation is with the clock. It can be beautiful; can simply show the time may be an indicator of the status of the owner. Concepts of car and smartphone with a flexible transparent screen

Smartphones can also perform the minimum number of required user functions, can be an indicator of "modernity" user, and may be the subject of prestige.



On the one hand, the ratios of the third vector (a measure of prestige) in a society are predominantly negative. But on the other hand, the third vector indicates the prospects of development of new technologies and consumer qualities of goods.


Make your own version of a fashion phone for girls and for boys.
Summarizing lesson






Locations of the lesson:


Case lesson takes place in the classroom. Carrying classes at the museum, park, library...



Teams of boys and girls.

The score of the competition between teams was

Targets for them:

 • What light output will fall on the smartphone screen area of 105 suare santimetres at a sunny day and at night under the artificial lighting? What part of the light flux is reflected, provided that all screen pixels are white?

• What is the probability of the phone, which replaced the screen during the year, card and battery?



Make 5 questions to the case lesson material (individual task).


Duration of Case:


90 minutes(double lesson).



Ability to circuit classes with student-double for:

It is possible



The results produced and competence:

- The ability to find quickly the necessary information on the topic and related thereto;

- The ability to use creatively the information to practical purpose;

- Mastering specific knowledge of chemistry, physics and other technologies sections (shown in the scan);

- The ability to "construct" knowledge-based receiving the information received and their segments;

- Upgrade intellectual and communicational skills.



electromagnetic wave, sound waves, light, light output, absorption, reflection, Mettlach, anode, cathode, electromagnetic reaction ion Odds



Larisa L. Hrabovska


Took part in case apgrade:



The End

«Knowledge always needs to be fresh!»

Interesting facts

During the life a person has such an amount of saliva that two swimming pools of medium size could be filled with it.

Found a mistake? Highlight the text and press Ctrl + Enter. We would be very grateful!

Found a mistake? Highlight the text and press Ctrl + Enter. We would be very grateful!