The IYNT Problems motivate our participants to perform exciting experiments and present their findings during the competition.

The Problems reflect a broad spectrum of phenomena and come from various natural sciences, and consequently each Problem is highly individual. We may assess various aspects and qualities of the Problems by looking at how they perform in the actual IYNT stages.

Difficulty: some Problems are never rejected, but others are rejected quite often. The probability of rejecting a Challenge can be used to parameterize the difficulty of a Problem. It is easy to calculate such a probability by dividing the number of rejections with the total number of Challenges in the Science Fighs with a challenge procedure. For any given Problem, the sum of probabilities to accept a Challenge and reject a Challenge always equals 1.

Relative popularity: some Problems are frequent at the IYNT. They are reported by many Teams and are likely to be selected for Semi-Finals or Finals. As the IYNTs are not equal in size and not every Problem is eligible for any Science Fight, it is appropriate to perform weighting and introduce a relative popularity of a Problem. If all Problems would be equally popular and Teams would have no preferences, each and every Problem would have a relative popularity of 1.

The graph (hi-res image) shows the interplay between difficulty and relative popularity of all 161 IYNT Problems. Each point is one Problem, while the point size reflects the absolute number of Reports and corresponding statistical weight. Albeit there is a trend that Problems that are always rejected are less likely to be popular, there are particular exceptions when a Problem is never accepted in Selective SFs but is chosen for Semi-Finals or Finals. Seven Problems have exceeded the average popularity of 1 by a factor or two or more.

Expected level of solutions: some Problems obtain higher Grades because the Teams are more likely to come up with stronger solutions. The global average for Average Points ⟨P⟩ for all Reports is an appropriate measure.

The graph (hi-res image) shows the interplay between difficulty and expected Average Points ⟨P⟩ of all 161 IYNT Problems (except 13 that never have been reported.) Each point is one Problem, while the point size reflects the absolute number of Reports and corresponding statistical weight. There is no clear upwards or downwards trend.

The raw data on each of the IYNT Problems is reflected in the Table below. Note that the sample sizes for all Problems are very small, and statistical uncertainties are high.

  • Column R14 shows the total number of Reports on the Problem in the SFs with a narrower choice of options (SFs 1 through 4, plus Semi-Finals in 2015, minus SF 2 in 2014);
  • Adjacent column shows the total number of options 14 available for the Challenge in such SFs, in other words the number of choices from which the Problem could be picked up;
  • Column R56 shows the total number of Reports on the Problem in the SFs with a broader choice of options (Semi-Finals and Finals, minus Semi-Finals in 2015, plus SF 2 in 2014);
  • Adjacent column shows the total number of options 56 available for the Challenge or selection in such SFs, in other words the number of choices from which the Problem could be picked up;
  • Column nsR shows the total number of Stages wherein this Problem could have been in principle reported;
  • Column × shows the number n× of Rejected Challenges for the Problem during the whole IYNT;
  • Column shows the total number n of Challenges for the Problem during the whole IYNT; note that n=n14+n× except six main problems accepted at Semi-Finals in IYNT 2013;
  • Column p× shows the probability of rejecting the Problem equal to n×/n; note that n=0 for six problems at IYNT 2014, where p× is set equal to ⟨p×⟩ for the respective IYNT and respective scale bar is black;
  • Column ψ shows the relative popularity of the Problem equal to (R14⋅※14+R56⋅※56)/nsR;
  • Column P shows the global average of all Average Points P earned by all Reports of the Problem.

2013-021611130240.50 0.57 14.0
2013-035621130060.00 1.73 14.6
2013-046511130170.14 1.37 17.6
2013-052631130150.20 1.50 19.1
2013-062601130240.50 0.40 17.2
2013-073601130360.50 0.60 17.7
2013-083601130250.40 0.60 20.0
2013-093501130470.57 0.50 20.0
2013-102531130260.33 1.43 22.5
2013-113521130160.17 1.23 19.6
2013-122521130260.33 1.07 20.4
2013-21360616030.00 1.13 16.2
2013-22260016350.60 0.75 16.7
2013-23460016370.43 1.50 17.9
2013-24260016130.33 0.75 24.0
2013-25160016120.50 0.44 17.6
2013-26460016150.20 1.50 17.3
2013-31260016350.60 0.75 19.6
2013-32560016270.29 1.88 15.8
2013-33360016250.40 1.13 18.1
2013-34060016441.00 0.00 18.1
2013-35360016250.40 1.13 17.3
2013-36360016030.00 1.13 17.2
2014-0151005050.00 1.00 21.2
2014-0201601613221.00 0.00 20.5
2014-0301601613000.44 0.00 20.5
2014-0401601613111.00 0.00 20.5
2014-0501601613000.44 0.00 20.5
2014-0601611613111.00 1.23 25.4
2014-0701611613000.44 1.23 21.0
2014-0801611613111.00 1.23 24.3
2014-0911601613010.00 1.23 12.9
2014-1011611613010.00 2.46 22.9
2014-1111611613010.00 2.46 23.6
2014-1201611613111.00 1.23 17.4
2014-1311601613010.00 1.23 11.1
2014-1401601613000.44 0.00 20.5
2014-1501611613000.44 1.23 22.5
2014-1601601613111.00 0.00 20.5
2014-1711611613010.00 2.46 24.8
2014-2116005010.00 1.20 18.2
2014-2216005120.50 1.20 16.8
2014-2306005111.00 0.00 20.5
2014-2416005010.00 1.20 23.5
2014-2526005020.00 2.40 14.5
2014-2606005000.44 0.00 20.5
2015-01330010250.40 0.90 18.2
2015-02430010150.20 1.20 14.4
2015-03330010470.57 0.90 18.8
2015-0431401429030.00 1.45 17.4
2015-0511411429340.75 0.97 19.8
2015-0641401429040.00 1.93 17.2
2015-0721401429020.00 0.97 17.6
2015-0821401429130.33 0.97 20.8
2015-0931401429140.25 1.45 19.4
2015-1011401429230.67 0.48 12.3
2015-1121411429130.33 1.45 22.8
2015-1221401429130.33 0.97 18.1
2015-1321411429240.50 1.45 19.7
2015-1421401429020.00 0.97 22.6
2015-1511401429230.67 0.48 15.5
2015-1601401429331.00 0.00 18.6
2015-1711401429340.75 0.48 12.9
2015-21160010010.00 0.60 18.2
2015-22460010040.00 2.40 23.4
2015-23160010230.67 0.60 23.4
2015-24260010020.00 1.20 18.6
2015-25060010111.00 0.00 18.6
2015-26260010130.33 1.20 13.8
2016-012311721570.71 1.10 17.4
2016-022301721240.50 0.29 22.0
2016-035301721160.17 0.71 19.7
2016-0411401744450.80 0.32 18.8
2016-0501421744551.00 0.77 19.4
2016-0631401744250.40 0.95 15.5
2016-0751401744380.38 1.59 18.9
2016-0841411744150.20 1.66 21.7
2016-0921411744020.00 1.02 19.6
2016-1031411744030.00 1.34 19.4
2016-1151401744050.00 1.59 18.2
2016-1231401744250.40 0.95 18.7
2016-1321421744130.33 1.41 17.3
2016-1431401744250.40 0.95 19.2
2016-1511421744230.67 1.09 18.9
2016-1601411744331.00 0.39 22.4
2016-1701411744551.00 0.39 18.8
2016-21360016140.25 1.13 14.7
2016-22060016221.00 0.00 18.4
2016-23560016050.00 1.88 17.8
2016-24260016130.33 0.75 17.2
2016-25160016230.67 0.38 22.0
2016-26560016050.00 1.88 15.1
2017-015511730160.17 1.40 16.8
2017-023511730580.63 1.07 17.4
2017-0355017305100.50 0.83 14.5
2017-042501730460.67 0.33 17.6
2017-053501730360.50 0.50 18.0
2017-0661201748060.00 1.50 15.0
2017-0721201748460.67 0.50 15.4
2017-0821221748240.50 1.21 20.3
2017-0931211748140.25 1.10 16.5
2017-1051221748050.00 1.96 15.9
2017-1131211748140.25 1.10 20.2
2017-1211211748010.00 0.60 18.0
2017-1311211748120.50 0.60 14.9
2017-1441201748040.00 1.00 13.4
2017-1531201748140.25 0.75 16.9
2017-1631211748030.00 1.10 15.5
2017-1731211748140.25 1.10 15.4
2017-21360018250.40 1.00 16.1
2017-22260018240.50 0.67 10.8
2017-23260018240.50 0.67 13.9
2017-24360018030.00 1.00 16.9
2017-25560018050.00 1.67 13.8
2017-26360018030.00 1.00 15.7
2018-013611727030.00 1.30 17.6
2018-022601727240.50 0.44 21.1
2018-031601727120.50 0.22 13.9
2018-042611727130.33 1.07 15.6
2018-054621727040.00 2.15 17.6
2018-063611727140.25 1.30 16.9
2018-072611727240.50 1.07 17.7
2018-084611727040.00 1.52 16.5
2018-095621727050.00 2.37 17.2
2018-102601727240.50 0.44 13.1
2018-112611727020.00 1.07 19.4
2018-120601727111.00 0.00 16.0
2018-133511727470.57 1.19 15.3
2018-143501727250.40 0.56 12.4
2018-153511727470.57 1.19 14.1
2018-164501727260.33 0.74 13.9
2018-172501727460.67 0.37 22.3
2018-21260015240.50 0.80 10.2
2018-22460015040.00 1.60 10.6
2018-23360015250.40 1.20 13.2
2018-24360015140.25 1.20 17.3
2018-25160015450.80 0.40 17.2
2018-26260015130.33 0.80 15.3
2019-013621733140.25 1.58 19.6
2019-025611733160.17 1.42 15.2
2019-036601733060.00 1.09 18.3
2019-042611733020.00 0.89 21.0
2019-052601733240.50 0.36 21.0
2019-063601733030.00 0.55 14.2
2019-075621733160.17 1.94 18.6
2019-084601733260.33 0.73 16.8
2019-092611733240.50 0.89 16.2
2019-103611733140.25 1.06 16.8
2019-115611733050.00 1.42 22.3
2019-122601733130.33 0.36 18.7
2019-135511733490.44 1.27 17.2
2019-1455017336110.55 0.76 19.2
2019-151501733450.80 0.15 19.0
2019-167511733290.22 1.58 18.1
2019-173511733360.50 0.97 11.7
2019-21460021590.56 1.14 16.5
2019-22360021360.50 0.86 19.0
2019-23260021130.33 0.57 17.2
2019-24460021590.56 1.14 19.4
2019-25660021170.14 1.71 17.2
2019-26260021350.60 0.57 16.5
2020-011601726120.50 0.23 tba
2020-023611726030.00 1.35 tba
2020-032611726130.33 1.12 tba
2020-041611726120.50 0.88 tba
2020-054611726040.00 1.58 tba
2020-063601726030.00 0.69 tba
2020-071601726230.67 0.23 tba
2020-084611726040.00 1.58 tba
2020-093601726250.40 0.69 tba
2020-101601726340.75 0.23 tba
2020-112621726240.50 1.77 tba
2020-123611726140.25 1.35 tba
2020-133501726250.40 0.58 tba
2020-142541726130.33 3.00 tba
2020-152501726240.50 0.38 tba
2020-163501726470.57 0.58 tba
2020-174501726370.43 0.77 tba
2020-21260014020.00 0.86 tba
2020-22260014130.33 0.86 tba
2020-23160014010.00 0.43 tba
2020-24360014140.25 1.29 tba
2020-25260014240.50 0.86 tba
2020-26460014040.00 1.71 tba

All IYNT Problems in one list

2013-01. Invent Yourself
Suggest your own research problem for the Tournament and solve it.

2013-02. The Bulb in the Glass
There is a popular way to force onions in а glass, filled with water (see figure). The bulb gives roots and leaves, and at the same time the volume of water in the glass decreases. What factors can influence the speed of water uptake? Test your hypothesis by experiment.

2013-03. Magnetic Arrows
Place two suspended magnetic arrows close to each other. After a short time they will reach the equilibrium where the opposite poles are aligned together. Deflect one of the arrows by some small angle and release it. Both arrows will start oscillations. Investigate and explain the character of the coupled oscillations of the magnetic arrows.

2013-04. Fresh and Salted Water
Electroconductivity of natural water depends on concentration of dissolved salts. The table below shows the conductivity of water samples taken from different natural sources.
1. Match the sample source with its conductivity
2. What might be the source of water with 13.2 μS/сm conductivity?
3. At the tournament you will be provided by a sample of water. Measure the electroconductivity of the new sample. Decide whether it is distilled water, tap water or mineral water. Please, bring with you the equipment for the electroconductivity measurement.
      Source                                                                             Conductivity (μS/сm)    
      Black Sea
      Dead Sea
      Baltic Sea at Neva estuary
      Lake Baikal
      Moscow-river, upstream of Moscow City (in winter)
      Peat bog lake
      Moscow-river, downstream of Moscow City (in winter)

Possible values of the electroconductivity, μS/сm: 10; 125; 420; 580; 4580; 45600; 228000.

2013-05. A Compass and a Ruler
Two schoolboys – Alex and Boris – got a task to make a given segment (initial length L) n times longer. Alex is allowed to use a compass and a ruler. Boris is allowed to use a compass only while he is asked to plot only the end points of the final segment. Suggest some way (or a few ways) of solving the problem for both schoolboys. Choose a solution Alex might use and let A(n) be a total number of lines drawn by the compass and the ruler in the solution for a segment of nL length. Choose a solution Boris might use and let B(n) be a total number of lines made by the compass for the points at nL length. Find A(2), A(3), ..., A(10) and make a bar diagram 1. Find B(2), B(3), ..., B(10) and make a bar diagram 2. Determine which solution is the best calculating A(n)/B(n) for each case separately. What reasonable assumptions about A(n) and B(n) behavior for all n can you make from the comparison of diagram 1 and diagram 2? For example, what can you tell about A(n)/B(n) behavior when n goes to infinity?

2013-06. Nontypical Crystals
Crystals of substances have usually form typical shapes. For example, the sodium chloride crystals are cubes, and the crystals of alum are octahedrons. Is it possible to grow untypically shaped crystals, for example, cube alum (or as some other shape, but not octahedrons)? Explain your opinion and prove it experimentally. You can use your own examples of crystalline substances.

2013-07. Fastidious Flour Moth
For several weeks Lucy as a tourist was enjoying a nice travel. At that time a flour moth (Anagasta) found a way to some food stocks in her kitchen. Coming back, Lucy found, that moth larvae appeared in porridge oat, in dry figs and ginger, in shelled sunflower seeds and hazelnuts. Flour moth paid less attention to dried plumes. Salt, sugar, roasted coffee grains, beans, cinnamon, cocoa powder, jam and peas remain intact. Explain the preferences of the flour moth. If possible, test in laboratory other 2–3 stocks as food for moth. Avoid the infection of your own food stocks by any moth!

2013-08. A Good Battery
While in class, physics teacher has noticed that the TV remote control is not working properly. He was thinking that its battery has died. At the end of the lesson he suggested that the schoolchildren do a scientific research to buy the best battery for the remote control device. That is how the competition “Who buys the best battery” has started. Carry out a similar research. Based on its results, suggest the best battery you can buy in the store.

2013-09. Plant Fertilizers
You have got sodium hydrophosphate, barium dihydrophosphate, potassium phosphate, potassium dihydrophosphate, potassium nitrate, sodium chloride, copper(II) chloride, cobalt(II) nitrate, zink sulfate, aluminium sulfate. What substances could possibly be used to prepare soluble fertilizers for desert cacti (fam. Cactaceae) and moisture-loving spiderworts (Tradescantia)? What precautions should be taken not to cause harm to the plants?

2013-10. The Land lease Contract
The chief of the tribe Chingachgook is settling a bargain with a cowboy Joe. The chief is about to turn over some of the Indian land to the cowboy, but only the land which Joe will be able to fence around with the help of four stakes and the same number of ropes tighten between each pair of stakes. The chief also has put forward the demand according to which the lengths of the ropes are to come to the quantities of (1−7t), (14t+5), (7−6t) and (5−3t) where t is a certain number. What is the value of t at which Joe will be able to fence the largest area and what is the size of that area?

2013-11. Flowering Chrysanthemums
Chrysanthemum indicum is a well-known autumn-flowering ornamental plant from India. Indira from Delhi sent a new large-flowered variety of chrysanthemum to her friends. Fatma planted those chrysanthemums in Istanbul, where they gave flowers on October 1st. Helen lives in Moscow, and Mary lives in Sydney (Australia). But their plants produced flowers at another date, rather than in Istanbul. Explain this phenomenon and calculate when Indira, Helen and Mary will see the flowering chrysanthemums, planted by themselves.

2013-12. A Fireproof Handkerchief
This problem was suggested by the team of Moscow Suvorov Military School in the home stage of YNT-2012 and received the highest score from the Jury. Please watch the video (see link below). Carry out the similar experiments on your own and explain the results. Make sure you follow the fire safety rules during the experiments! The presence of your teacher is required!

2013-21. Onion
Prepare a thin layer of onion skin in water. Observe this layer at moderate magnification. Touch a salt powder with a wet needle. Place a few salt crystals in the field of view such that the crystals are visible in the telescope. Observe the behavior of the onion cells. Perform a similar experiment with the sugar crystals and compare the results. Explain the observed phenomena.

2013-22. Toilet paper
Take a carton tube from the roll of toilet paper. Close one of the open ends of the tube with a piece of toilet paper and fix it with a rubber ring. Fill the tube with salt and try to push the salt towards the closed end. Observe and explain the effect.

2013-23. Tea bag
Produce a standing vertical cylinder from an empty tea bag and ignite it from the top. Observe and explain the flight. Estimate the quantitative parameters. What happens if four tea bags standing close to each other are ignited at once?

2013-24. Soot on a paper card
Place a paper card above the flame of a candle. Describe the dependence of the soot spot on the distance between the flame and the card.

2013-25. String telephone
Produce a string telephone with a maximum range of operation and sound quality.

2013-26. Sunny spot
Produce a reflected light spot on a nearby wall. Investigate its shape. Now produce a similar spot on a remote wall. Compare and explain the two shapes.

2013-31. Sliced potato
Slice a potato into a large number of long similar rectangular bars 5 cm long. Prepare stock solutions of NaCl of six various concentrations from zero to a saturated solution. Place the slices into the solutions. Observe and investigate the behavior of the slices.

2013-32. Matches
Remove the striking surface from the side of a match box. Push the matchbox with a ruler along the edge of a table with various mutual orientations of the ruler and of the box. Observe and investigate the motion.

2013-33. Potato battery
Construct a power cell with a maximum output voltage powered by a potato.

2013-34. Blind spot
Draw a cross and a dot on a sheet of paper. Close an eye while looking at the cross from various distances. Explain the disappearance of the dot. Now draw a line passing through the dot. Repeat the test and explain the results. Try also with various lines and colors.

2013-35. Chemical colors
Produce as many colors as possible using the chemicals you are offered.

2013-36. Cagliostro's resistor
Produce a resistance of 3.75 Ohm using 10 resistors 10 Ohm each.

2014-01. Invent yourself
Formulate an open problem on your own and solve it. Topic: experiments using a microscope. Allowed magnification: from 10X to 40X.

2014-02. Potatoes
A classic board, as understood by carpenters, is a rectangular parallelepiped with significantly varied linear dimensions (length>width>thickness.) They call such a parallelepiped a bar if width and thickness are comparable. If all three dimensions are comparable, they call it a cube. When a homogenous board floats on the water surface, its biggest face is horizontal. A board “knows” perfectly this rule and always “abides” to it. But for a bar the rule becomes ambiguous and its behavior is determined by ratio of its density to water density. For a cube, it is even more “ambiguous” in this regard. Use potatoes for an experimental investigation of floating bodies of different shape. Regulate the density ratio through adding salt to water. Investigate the different ways of how bodies of various shapes can float.

2014-03. Discovery of chemical elements
Name ten most common chemical elements in the Earth crust. For one of them describe and, if possible, reproduce as many as possible of the experiments through which this element has been discovered.

2014-04. Pulse
Investigate how human pulse depends on the speed of running and fitness of the human. Come up with a parameter characterizing the fitness. Estimate how much energy the human spends on running in addition to normal body functions.

2014-05. Last droplet
A beaker is filled to the brim with water that dips into the middle of the beaker from a low height. Can you estimate what droplet will be “the last straw”, i.e. the drop that will make the water to spill over the edge of the beaker?

2014-06. Water on the Earth
The modern astrophysics states that the World Ocean emerged on the Earth due to a lengthy and intensive comet bombarding at a certain stage of the Solar System formation. Find out as many parameters of this grandiose phenomenon as you can.

2014-07. Tourist route
You are a manager at a travel agency developing sport and sightseeing trips. In a summer, a family with children wishes to make a week-long trip from Paris to Düsseldorf. They wish to cover part of the route on a bicycle (no more than 50 km per day) and part of the route on regional trains (no more than 2 hours per day.) Since the children have to sleep during the night, the travel should not start before 10 a.m. and finish after 8 p.m. on any day. The overnight stays should be possible at camping sites where pitching a tent is allowed. The trip should pass through interesting places.
Suggest a journey plan to the family and specify the following for each day: mileage on the bicycle, duration of train connections, highlights of the sightseeing. List the online resources required for a detailed planning of the travel. Take into account the usability of the services given the fact that the tourists speak only English.

2014-08. Droplet
Place a droplet of salt water on a glass plate and study the process of drying. How does the deposit of dried droplets depend on the salinity of water? Perform the same with a droplet of black tea.

2014-09. Traffic lights in a test tube
Volodya the fifth grader decided to collect as many liquids of various colors as possible in one tube. He succeeded to produce the “chemical traffic lights” as shown. Try to beat Volodya’s record.

2014-10. Straw
What is the maximum length for a vertical straw such that you still can drink non-carbonated water through it? Still can drink cola through it?

2014-11. Colorful bouquet
It is known that the color of a carnation flower can be changed if the flower is watered with an ink solution. Can the color of the flowers be changed by other methods? Explain the principle of your method. To what flowers is it applicable?

2014-12. Foxes and penguins
There are certain regularities in the distribution of closely related species of warm-blooded animals. For example:
1. North Africa is home for the smallest and long-eared Fennec Fox, and tundra is home for the bigger Arctic Fox, which has shorter ears and legs. The regular fox is something intermediate between them.

2. The biggest of the penguins, the Emperor Penguin (height over 120 cm), lives on the Antarctic coast; while the smallest, the Galapagos Penguin (height about 50 cm), lives in the tropical belt near the coast of South America.

Identify and explain the regularities in the distribution of warm-blooded animals across the Earth. Show your own examples evidencing these regularities.

2014-13. Format of photos
You have a photograph in the BMP file format (a natural scenery or a portrait.) Convert it to the JPG file format. The differences are nearly invisible though they exist. Propose a visual method to demonstrate these differences.

2014-14. Weight loss
Weigh yourself on a “good” balance immediately before the going to the bed in the night and then immediately after waking up. Did you detect a difference? Explain the results. Besides, what balance would you consider a “good” balance?

2014-15. Four points
Do the following experiment: put points at arbitrary positions on several sheets of paper, four points per each sheet. Suggest other participants of the experiment (e.g., members of your team) to do the same. Now connect sequentially these points with straight line segments so that they form a quadrilateral (cases in which a triangle or just a straight line are formed, should be discarded.) Now count the total number of the quadrilaterals (N) and the number of convex quadrilaterals (n), and calculate the ratio k=n/N. Likely to be that k>0.5.
Question: What is k for a very large N and why, if:
a) the experiment is performed by a computer and visualized on the display?
b) the experiment is performed by a computer, but is not visualized, and is carried out in a mathematical program?
c) the experiment is performed a large number of people?
d) a real experiment is not performed, but you find the ratio theoretically if N tends to infinity?

2014-16. Potatoes again
If a freshly dug potato tuber, or a tuber stored in a dark room, is left in the sunlight, its surface becomes green. Why does this happen? And what would happen to the color of the tuber if it is put again into a dark room for a long time?

2014-17. Measurement of color sensitivity
Some people (called color blind persons) have difficulties comparing the colors of two objects. But most people perceive the color difference at the first glimpse. The difficulties arise when the colors are hardly distinguishable, e.g. if colors of two leaves from the same tree need to be compared. How is it generally possible to quantitatively estimate the ability of a person to distinguish the color shades? Is a single numerical parameter sufficient, or a more complicated evaluation system is required?

2014-21. Density
One vessel is filled with fresh water. Another vessel is filled with salt water. Determine the density of the salt water assuming that the density of the fresh water is 1 g/cm3.

2014-22. Chemistry
Five test tubes contain aqueous solution of copper sulfate, ammonium sulfate, sodium carbonate, iron sulfate and calcium chloride. Determine what substance is in each test tube.

2014-23. File
You have a file called Dickens.doc. Produce another file containing the entire text and preserving the font size and style, structure of paragraphs and other attributes, but having the smallest possible file size in bytes.

2014-24. Square
Cut a rectangular figure out of a paper sheet sized 9×20. Now cut it into constituting parts such that one could put these parts together into a square.

2014-25. Sugar tower
A sugar tower is two or more stacked sugar cubes. Drip a few water droplets onto the top sugar tube and observe how the tower is destroyed. Explain the observed phenomena. We suggest to carry out simultaneous experiments with several towers and consider the number of cubes in a tower N and the number of droplets K as the variables.

2014-26. Ping pong
Demonstrate a neutral buoyancy using a ping pong ball, plasticine, salt and water such that the ball does not lift and does not sink.

2015-01. Invent yourself: Physics
Topic: precise weighting. Study the physical effects that influence precise weighting of solid objects with a mass of 10 to 100 g.

2015-02. Invent yourself: Biology
Topic: microorganisms. Suggest an investigation of such cases that allow for a quantitative study and reproducible measurements.

2015-03. Invent yourself: Chemistry
Topic: chemistry of potatoes. The ‘life’ of one potato tuber, from its growth in soil, to storage, and finally to human use such as boiling or production of chips, is a lengthy chain of chemical processes. Select and study one or several links of this chain.

2015-04. Sunset
The visible Sun disk touches the horizon and after a particular time interval disappears behind the horizon. What is the duration of this time interval? Explain the optical phenomena observed during a sunset.

2015-05. Falling ball
An electronic balance (1) is connected to a PC (5) in order to record the time dependence of the measured weight. A light frame (4) is mounted on a tall beaker (2) filled with water. The frame has a holder (3) allowing controlled release of a small ball such that it falls into the water. The beaker is placed on the balance as depicted in the Figure. Investigate how the readings of the balance reflect the different phases of the motion of the ball.

2015-06. Disappearing ink
Suggest a chemical formulation for the ink that would disappear after used to write a text. What parameters determine the time when the text becomes invisible? Is it possible to process the paper in such a manner that the text appears again?

2015-07. Pancakes
It is argued that pancakes can be so good looking that they ignite appetite by their appearance only. Suggest grounded scientific criteria to parameterize how appetizing the pancakes are.

2015-08. Library
One person has decided to download all of the fiction existing in the English language and store it on a single USB stick. He expects to find or generate the respective text files, compress them, and then index them conveniently. Is this ambition realistic? Suggest a plan to approach this goal and solve a partial problem of this plan.

2015-09. Distances in open space
How do astronomers measure distances between the planets of the Solar System, between the stars in our Galaxy, or between the galaxies? Determine the distance between the two space objects of your choice.

2015-10. Ice hole
You have drilled two ice holes in a frozen lake on a frosty winter day. One ice hole is close to the shore, while the other ice hole is far from the shore. Surprisingly, the height difference between the ice surface and the liquid water is different for each hole. How can you explain this? How can one use this height difference to determine the local ice thickness?

2015-11. Puzzle in a beaker
A researcher decided to measure the diffusion rate of ammonia in gelatin. He added some magnesium sulfate to the hot gelatin solution which set to a gel on cooling. He then poured some aqueous solution of ammonia onto the gel and left the beaker for two days. The researcher was surprised to discover white layers of precipitate in the beaker, as depicted in the Figure. Explain this phenomenon and determine what does the number of bands depends upon.

2015-12. Structure of a hair
The hair of various animals may significantly differ in their structure. What are these differences and how can you explain them?

2015-13. Shining orbs
Bright and rather unexpected white disks may appear in a photo taken with a flash in a dark room. Explain why such shining orbs appear in the photos.

2015-14. Galton box
In the Galton box, a regular 2D lattice of obstacles disperses a thin flow of falling particles. When falling on the bottom of the box, the particles show a normal distribution. Use various types or particles and different arrangements of the obstacles to find the conditions when the distribution is no longer normal.

2015-15. Fly
A fly can easily walk on a ceiling. How is this possible? Can one find such a ceiling that the fly would be unable to walk on?

2015-16. Smoke ring cannon
Construct such a vortex ring cannon that would shoot with smoke rings on a distance sufficient to hit the chairperson of your Science Fight.

2015-17. Starch monsters
A water suspension of starch is placed on a loudspeaker. Investigate and describe the resulting starch monsters.

2015-21. Horizontal Level
A red dot is marked on a wall in your Science Fight room. Put a blue dot on another wall at exactly same horizontal level.

2015-22. Pouring Water Out
Compare several methods to empty a bottle of water and indicate the fastest method.

2015-23. Granulated Sugar
Determine an experimental distribution of sizes of particles of granulated sugar.

2015-24. Chemistry
A list of four compounds includes CuSO4, K2Cr2O7, MgCl2, NaCl. Three of those are in three marked test tubes. Determine the contents of each test tube.

2015-25. Non-Linear Vial
You are given a vial loaded with metal nuts and closed with a cap. The vial floats on water if immersed vertically with the cap upside. However it sinks if put in water with the cap downside. Investigate and explain this behavior.

2015-26. Bitmap
Several bitmap files have the same size and contain look-alike images. There is however a particular variance between the images. Identify and parameterize this variance.

2016-01. Invent Yourself: Air Traffic
Some web services, e.g. Flightradar24, aggregate and provide data on positions, altitudes, speeds, and other parameters of almost any commercial flight in the World. Suggest an investigation of an interesting scientific aspect of air traffic or flights using such data.

2016-02. Invent Yourself: Weather Forecast
It is often argued that some of weather lore is true and has predictive value. Suggest a scientific test of two popular sayings forecasting respectively short-term and long-term weather trends.

2016-03. Invent Yourself: Human Reaction Time
The time of human reaction to sound, light, and other stimuli is an interesting parameter. What does this time depend on? Propose an interesting experimental study that concerns the time of reaction.

2016-04. Van der Graaf’s Cat
A cat may crackle when petted. Parameterize and investigate the static electricity in cat’s fur. How can one make this static discharge stronger or weaker?

2016-05. Tempest in a Glass of Water
When water is poured into a glass, its dynamics is complex and intense. Even when the liquid surface settled down, it may take time before the water flow slows down and stops. Investigate this storm in a glass.

2016-06. Dice
In many games, dice are thrown to obtain random results. How does the result of a die roll depend on its height above a table, if the die is released at zero initial speed?

2016-07. Plants in Motion
Various plants can turn in response to the position of the sun or other light sources. Investigate this motion experimentally and theoretically.

2016-08. Zipf’s Law
Human language is described by unusual distributions. Take your favorite book and count how many times the most frequently appearing word (rank one) appears; the second most frequent word (rank two) appears, etc. Investigate and explain the dependence of the word count on its rank in the frequency table. Would it be the same for another book in the same or different language?

2016-09. Cinder
In the Middle Ages, people used to wash the cloth in cinder. Study the effectiveness of cinder in washing clothes.

2016-10. pH Indicator
The juice of many fruits or vegetable crops contains a natural pH indicator that changes colors according to the acidity or basicity of the solution. Investigate such pH indicator juices and their mixes. Propose the most precise and effective composition and compare its properties with those of common indicator paper.

2016-11. Corrosiveness of Cola
It is often argued that cola is so corrosive that can be used to clean metal objects. Investigate this property of cola.

2016-12. Ants and Food
Investigate what food attracts ants. Try different foods and introduce parameters to describe the reaction of ants.

2016-13. Firelighting
Investigate various methods to start a fire by friction.

2016-14. Effervescent Tablet
The rate of some chemical reactions may depend on surface area. Break effervescent tablets into smaller parts, or stir them into powder, to study how the dissolution rate depends on the surface area.

2016-15. Mountain Peaks
What methods are used to determine the elevation of the World’s highest mountains? Suggest your own experimental method and determine the height of a mountain or a hill of your choice.

2016-16. Two Shovels
Sink two metal shovels deep into the soil outdoors, e.g. in a garden or in a field. Determine the dependence of the resistance between the two shovels on the distance between them in a sufficiently wide range, e.g. 0 to 25 meters.

2016-17. Swadesh List
Many words in related languages (e.g. Kazakh and Turkish, or Croatian and Belarusian) can match or differ by a few sounds only. Study this similarity quantitatively for the language pairs of your choice. When did these languages separate from a common ancestor?

2016-21. Oxygen
Using any chemicals of your choice, produce a flask of oxygen. Prove that the oxygen concentration in the flask is higher than in the ambient air and determine the concentration.

2016-22. Glycerol and water
Determine experimentally how the viscosity of glycerol-water mixtures depends on the ratio of components. Use the tools and materials of your choice.

2016-23. Colors of the rainbow
You are given aqueous solutions of potassium dichromate (K2Cr2O7) and copper (II) sulfate (CuSO4). By mixing these two solutions in any combination with colorless solutions of your choice, obtain as many test tubes showing distinctly different colors as possible.

2016-24. Density
You are given a small irregularly shaped object. Determine experimentally its density.

2016-25. Tuning fork
Determine the frequency of a tuning fork with one or several experimental methods.

2016-26. Soap boat
Make a flat soap powered boat from paper or plastic. Investigate the parameters affecting the maximum speed of the boat.

2017-01. Invent Yourself: Good guesses
In 1906, Francis Galton observed a contest where 800 farmers guessed an animal's weight. To his surprise, the median of the guesses was within 0.8% of the true measured weight. What is the chance of obtaining such a good match by coincidence? Select an interesting and important parameter, measure it directly, and give a group of human observers the task to guess the value of the parameter. Discuss the results of your experiments.

2017-02. Invent Yourself: Time-lapse videos
Propose a very slow physical, biological, or chemical phenomenon that can be studied and visualized using time-lapse photography. Produce and demonstrate such a video.

2017-03. Invent Yourself: Curved mirrors
Suggest and demonstrate interesting experiments in which large concave mirrors can be used to heat up or cool down various objects.

2017-04. Invent Yourself: Language barriers
Speakers of related but different languages or dialects can sometimes understand each other, without any prior intentional study. Propose an interesting study of such a mutual intelligibility. Investigate it experimentally for the pairs of dialects or languages of your choice. Introduce and determine quantitative parameters.

2017-05. Invent Yourself: IYNT grades
An upwards of four thousand grades that Jurors have given in Science Fights of previous four IYNTs can reveal properties and hidden regularities of the IYNT grading. Suggest an interesting hypothesis that concerns the IYNT grades and test it with real data from previous IYNTs.

2017-06. Apples
Why do apple slices turn brown after being cut? Investigate the speed of this process and test methods to prevent browning of apple slices.

2017-07. Growing through asphalt
Can a little plant grow straight up through concrete or asphalt?

2017-08. Tonic water in UV light
Tonic water glows brightly when exposed to an ultraviolet black light bulb. It is however easy to quench the glow of tonic water by adding salt. Investigate this effect. What other common substances glow under UV light and how can one influence their glow?

2017-09. Salt production
Solar evaporation of seawater or salt mining are common methods to produce common salt (NaCl). Propose a method to extract salt from a natural source and determine both productive capacity of your method and purity of the product. Demonstrate an amount of salt produced by your method.

2017-10. Rijke's tube
If air inside a vertical cylindrical tube open at both ends is heated, the tube produces sound. Study this effect.

2017-11. Grow light
Investigate how different types of artificial lights affect plant growth. What is the role of light spectrum?

2017-12. Milk
Develop simple methods allowing determination of some of the important properties of milk. Suggest an investigation requiring comparison of various milk samples.

2017-13. Allometry
How do length and thickness of bones scale with overall size and weight of animal?

2017-14. Routers and garden cress
In 2013, five young students claimed a sensational discovery that garden cress (Lepidium sativum) won't germinate when placed near two Wi-Fi routers. Reproduce their experiments under controlled conditions to support or dismiss their conclusions.

2017-15. Water from the air
Design and construct a device allowing collection of water by condensing moisture from air. Determine if the water obtained with your device is suitable for drinking. What amount of water is possible to collect during one Science Fight?

2017-16. Paper wrinkles
When a piece of paper dries after being wet, it can get wrinkled. Investigate and explain this phenomenon.

2017-17. Tornado machine
Build a machine to produce an indoor air tornado. Investigate the properties and stability of the tornado. Is the machine portative enough to be demonstrated at a Science Fight room of the 5th IYNT?

2017-21. Trampoline
Stretch a rubber membrane and investigate how a small ball bounces off the membrane depending on the degree of stretching regarding the fixed height of the falling ball.

2017-22. Airbag
Use plastic bags and a compressor to lift a bag above the floor level. One can also try to sit on it. Determine all relevant properties of your setup.

2017-23. Rotating light
Some molecules have a property called optical activity: they rotate polarized light. This property can be observed using a polarizer and a laptop/phone screen as a source of plane polarized light. Investigate the optical activity in solutions of glucose, fructose, sucrose, and penicillin V to find the beaker containing fructose. Try to specify the other beakers. Note, there are two beakers with one of the compounds.
D-Glucose (+53 [deg·dm−1·cm3·g−1] specific rotation clockwise), D-Fructose (−92 [deg·dm−1·cm3·g−1] specific rotation counter-clockwise), Sucrose (+66 [deg·dm−1·cm3·g−1] specific rotation clockwise), Penicillin V (+223 [deg·dm−1·cm3·g−1] specific rotation clockwise.)

2017-24. Mysterious amylase
An enzyme called amylase catalyses the hydrolysis of starch into sugars. Select a chemical test for starch, find convenient sources of amylase and starch, and investigate how much time of exposure to amylase is needed for the starch test to not be observed.

2017-25. Battery
Use zinc and copper plates, as well as other materials of your choice, to assemble a battery. Investigate its relevant properties.

2017-26. Bouncing ball
Make a small hole in a ping pong ball, fill it with some liquid and seal the hole. Drop the ball from the fixed height and investigate how high it bounces, depending on the amount of liquid inside.

2018-01. Buffon’s needle
Draw a series of parallel equally spaced lines on a horizontal surface. Pick a bunch of sticks (e.g. matches or needles) slightly shorter or longer than the separation between the lines, and randomly drop them on the surface. It is claimed that the number of times the sticks cross the lines allows estimating the constant π to a high precision. What accuracy can you achieve?

2018-02. All roads lead to Rome
Open a random Wikipedia article and click on the first link in the article. Keep clicking on the first link of each following article. It is argued that you will quickly end up on the page Philosophy. Investigate whether this is true. How can one describe such an observation?

2018-03. Annoying foreground object
Look at a flat photograph. What methods allow you to tell which objects were closer and which were farther from the camera when the shot was taken? Design and create a photograph that violates the intuitive judgment of relative distances.

2018-04. Making quark
Quark, cottage cheese, and similar varieties of white acid-set cheese can be produced from milk. Investigate this process experimentally and study the properties of the resulting product.

2018-05. Collision
A highly elastic Super Ball collides with a rigid surface. How can one determine the collision time? Propose various techniques and compare the experimental results.

2018-06. Eye color
In certain human populations, genetics allows predicting inheritance of eye color among family members. In other populations of the present day World, nearly everyone has the same eye color. What information is it possible to determine about the eye colors in both distant and close ancestors, descendants, and relatives of one living person?

2018-07. Worms
Earthworms change the mechanical properties of soil and make the soil more porous. Investigate this process and introduce quantitative parameters.

2018-08. Fair coin
In many cases, disputes are resolved with a coin toss. It is presumed that this procedure gives equal chances of winning to both sides. Investigate how the chances depend on the tossing mechanism and the coin properties.

2018-09. Bottle tone
Take an empty bottle and blow air across its mouth to produce a sound. Now fill the bottle with some water and study how the sound changes.

2018-10. Greenhouse
A hot object placed in the open air would gradually cool down. We can slow down this process by containing the object in a greenhouse. Compare different mechanisms of heat loss by the object and explain how the presence of a greenhouse affects them.

2018-11. Fame
Some people in the modern World are considered ‘famous’ since they frequently appear in the news, TV, and social media. Suggest a quantitative parameter of such ‘fame’, and build lists of persons that are sorted according to this parameter.

2018-12. Occulted stars
Investigate the optical effects that can occur when the Moon passes in front of a star.

2018-13. Invent Yourself: Blood pressure
Study the accuracy of various methods to measure blood pressure. Propose an interesting study involving blood pressure and pulse.

2018-14. Invent Yourself: Dendrochronology
Annual growth rings of trees are often used to date important historical events or environmental conditions of the past. Suggest and perform an investigation using various tree rings samples.

2018-15. Invent Yourself: Laser pointer
Suggest an interesting optical study involving a beam from a laser pointer.

2018-16. Invent Yourself: Granular materials
Suggest a study involving properties and behavior of granular materials.

2018-17. Invent Yourself: Chronophotographic gun
Étienne-Jules Marey pioneered the use of time resolved photography to study physiology of humans and animals, and in particular their postures and locomotion. Propose a quantitative study of important physiological functions or parameters that would require analysis of similarly taken videos.

2018-21. Lung volume
Determine the lung volume of a human with the best possible precision. Is it possible to detect differences in lung capacities for each member of your team? Is it possible to apply your method to determine the lung volume of your opponent during the Science Fight?

2018-22. Montgolfière
To heat air for a simple hot air balloon, one can even use a heater. Build such a buoyant object. Explain the results of your experiments and determine important parameters.

2018-23. Magdeburg hemispheres
Prove the existence of atmospheric pressure using various beakers, a piece of paper, and other equipment of your choice. Is it possible to estimate the value of the atmospheric pressure?

2018-24. Mysterious catalase
An enzyme called catalase influences on the rate of decomposition of hydrogen peroxide. Make tests to identify catalase-positive and catalase-negative organisms and materials.

2018-25. Damped pendulum
Determine the decay time of a pendulum.

2018-26. Dominoes
Stand a number of domino tiles in a long row and topple the first tile. Investigate the speed of toppling dominoes. Does it depend on the distance between the tiles?

2019-01. 2D foam
Soap foam enclosed between two glass sheets appears as a network of polygons. Such foams evolve with time, as individual bubbles move and coalesce, and the liquid drains out. Investigate the structure and evolution of 2D foams.

2019-02. Mountains
What are the tallest mountains in the Solar System? Propose and analyze the theoretical models that can allow predicting the maximum altitudes of mountains on various celestial bodies.

2019-03. Salty soils
Saline soils may affect plant growth. How do salts affect the growth and development of plants?

2019-04. Sunflower spirals
Patterns of seeds in the head of a sunflower have a very specific geometric structure. How can one describe and explain such a structure? What other plants demonstrate similar geometric patterns in their leaves or seeds?

2019-05. After the tempest
Take two beakers of water and use a spoon to stir water clockwise in one beaker and counterclockwise in the other beaker. Observe the beakers after a sufficiently long time when the water flow has slowed down. Is it possible to determine the original direction of water flow after 1 hour? 1 day? 1 week?

2019-06. Soundproofing
It is sometimes necessary to reduce unwanted noise in a closed space. Test various methods to soundproof your room.

2019-07. Burning glass
Propose and test various methods to start a fire with a magnifying glass.

2019-08. Smells
Smells spread through the air, however it would take some time before a human nose is able to detect the smell. Study different aspects of odor diffusion and sensation of odor by humans.

2019-09. Fading in sunlight
Printed pages fade in direct sunlight, especially if certain types of ink and paper are used. Propose quantitative parameters to study the prolonged exposure of ink and paper to sunlight.

2019-10. Elastic bones
Chicken bones kept in acidic conditions for a few days become elastic. Perform such an experiment in controlled conditions and investigate what components of bones are responsible for their mechanical properties.

2019-11. Yeast
Investigate the rate of the multiplication of yeast at different temperatures.

2019-12. Moon
The apparent size of the Moon perceived by an observer depends on multiple factors. Investigate these factors and their role.

2019-13. Invent Yourself: Baking bread
Distinctly different types of bread are produced by varying methods of baking, proportions of ingredients, and types of flour. Suggest an experimental and theoretical study of how one or several bread varieties are baked.

2019-14. Invent Yourself: Eye movements
Human eyes are in constant involuntary and voluntary motion when exposed to visual stimuli, such as scene viewing, reading or tracking a moving object. Use eye movement data to select and study an interesting psychological effect concerning perception of images and motion, in humans or in animals.

2019-15. Invent Yourself: Fractals
Propose an interesting experimental and theoretical investigation involving fractal geometry.

2019-16. Invent Yourself: Short-term memory
What is the capacity and duration of human short-term memory? Suggest an experimental study to evaluate short-term memory and factors that may have important influence.

2019-17. Invent Yourself: Atmospheric electricity
Electric field is present in the atmosphere even in good weather. Suggest an interesting problem concerning atmospheric electricity.

2019-21. Resolution of naked eye
Introduce one or several parameters to describe angular resolution of an unaided eye. Determine the values of this parameter for each member of your team.

2019-22. Cold and warm
When dissolved in water, sodium carbonate and ammonium nitrate have a property to significantly change temperature of the solution. Obtain highest and lowest temperatures of respective solutions.

2019-23. Upside down
A glass filled with water and covered with a paper card can be turned upside down. What minimum amount of water in the glass is required for this trick?

2019-24. Electromagnets
Produce an electromagnet and investigate some of its important properties.

2019-25. Paper airplanes
Construct a paper airplane using an A4 paper sheet. Investigate the conditions ensuring the longest distance of its flight.

2019-26. Candle oscillator
Two horizontal needles are used to balance a candle so that it rotates freely. If the candle is lit at both ends, it starts to oscillate. Explain and investigate this effect.

2020-01. Left-handed animals
Some animals have a preference for using one side of their body, similar to left-handed and right-handed humans. Perform experiments to obtain statistical data and investigate paw preferences of various animals.

2020-02. Slow match
A cord in which the flame front propagates with a constant low speed has been important to ignite cannons. Produce such cords and investigate their burn rates and other properties.

2020-03. Photography with iron salts
Mix 10 parts of ferrous oxalate (25% aqueous solution), 7 parts of concentrated ammonia solution, and 20 parts of saturated solution of oxalic acid to produce a photosensitive iron complex. Prepare separately a 25% solution of potassium ferricyanide. A sheet of paper saturated with a mix of these two solutions can be exposed to light and produce an image. What other iron salts are photosensitive? Produce photographs using various approaches and various iron salts, and investigate the role of relevant parameters.

2020-04. Popping buoy
A light ball is held underwater and then released. The ball may sometimes pop above the water surface. Investigate this effect and the role of important parameters.

2020-05. Disinfectants
Prepare sterile culture dishes and investigate the growth of door handle bacteria and other common microorganisms. Investigate how various disinfectants, such as antibacterial soap, affect the bacteria.

2020-06. Piezo ignition
A common lighter uses piezoelectric crystals. Investigate the quantitative parameters describing the response of such crystals to pressure.

2020-07. Caoutchouc
Milky latex is present not only in commercially cultivated rubber trees, but even in houseplants such as spurge or ficus. Produce natural rubber from plants of your choice and investigate the physical and chemical properties of the rubber.

2020-08. Magnet and matchstick
A matchstick is not attracted to a magnet, however the head of a burned matchstick is attracted by a strong magnet. Investigate the reasons and the role of relevant parameters.

2020-09. Venus flytrap
Investigate experimentally how Venus flytrap (Dionaea muscipula) catches and digests its prey.

2020-10. Variable stars
Some variable stars, in particular Algol (β Persei), have sufficient magnitude to be observed with unaided eye or simple telescopes. Measure the light curve for such a star. What information can be obtained from the light curve?

2020-11. Hydrogen release
A simple method to produce gaseous hydrogen is the reaction between metal aluminum and two salts in aqueous solution (e.g. copper sulphate and sodium chloride). Investigate how the reaction rate depends on the concentration of each salt and other relevant conditions. What salts react with aluminum to release hydrogen?

2020-12. Onion cells
Investigate the effects of various salts on the structure of onion cells.

2020-13. Invent Yourself: Hearing
Each speaker can pronounce a vowel on several pitches, yet a listener is likely to recognize the phoneme (e.g. /o:/ or /u:/). Astonishing auditory illusions (e.g. Yanny and Laurel), so called mondegreens, and experiences of persons with poor hearing demonstrate nevertheless that listeners perceive sounds, words and phrases differently. Propose a problem concerning speech perception, mishearing, or physical differences between sounds of spoken language.

2020-14. Invent Yourself: Chemical oscillators
Examples of oscillating chemical reactions are the Briggs-Rauscher reaction or the Belousov-Zhabotinsky reaction which result in periodic color changes. While some of such reactions are difficult to reproduce, there are multiple ways to produce a simpler and more reliable chemical oscillator. Propose a problem about an interesting and simple chemical oscillator.

2020-15. Invent Yourself: Tasting food
Volunteers are given the task to judge the taste of food samples using a quantitative parameter. The results may depend on multiple factors (e.g. hunger or satiety, age of individuals, or temperature of food). Is it possible to detect statistically significant differences? Propose a study concerning the perception of taste.

2020-16. Invent Yourself: Soap production
Vegetable and animal oils and fats are historically used to make soap. Investigate how physical and chemical properties of such soap depend on ingredients and recipes, and propose an interesting problem concerning soap-making from easily accessible ingredients.

2020-17. Invent Yourself: Weight
The weight of a living organism is not constant. Propose an interesting study concerning short-term or long-term variations in the total body mass of a living organism.

2020-21. Reaction time
Measure your reaction time by asking a colleague to drop an object between two almost closed fingers or hands and trying to grab it. Is it possible to detect differences in the reaction time between members of your team?

2020-22. Blinking
Ask several members of your team to volunteer for three tests: blink normally; blink as frequently as they can; do not blink for the longest possible time until they feel uncomfortable or blink involuntarily. Measure each frequency and analyze the results.

2020-23. Time goes backwards
Produce a video showing a natural phenomenon in reverse motion. Select such a phenomenon that your video looks the same if played forward or backward.

2020-24. Oscillations in water
Take a vial, a tall glass, or a bottle and load it with heavy objects. Make it float vertically on the water surface. If displaced up or down, the vial will oscillate. Calculate theoretically and measure experimentally the period of its oscillations.

2020-25. Piles of powder
A powder of your choice is poured onto a table, e.g. through a tube or a funnel. Investigate how the height of the pile depends on time. Investigate how the shape of the pile depends on time.

2020-26. Steamed up mirror
When one blows air on a mirror or a window pane, it gets foggy. Investigate this effect.

2021-01. Coin in a balloon
An inflated air balloon contains a coin and is gently moved to set the coin rolling around the inside of the balloon. Explain and investigate the buzzing sound produced in this experiment.

2021-02. Liquid layers
Water and vegetable oil do not mix and form two layers in a beaker. It is possible to fill the beaker with many more layers of immiscible fluids. How many layers can you obtain? Investigate the motion of the interfaces if the beaker is disturbed or shaken.

2021-03. The Purkinje shift
As light levels decrease, human eyes perceive relative brightness and contrast of various colors differently. Perform experiments in controlled conditions to investigate this effect.

2021-04. Making butter
Investigate the methods to produce homemade butter from milk or cream. Investigate how properties of the butter depend on relevant parameters.

2021-05. Lake water
A drop of water from a natural pond may contain bacteria, archaea, algae, fungi, protozoa, and other organisms. Perform observations to identify as many species of living organisms as possible. What are the chances that another drop contains a different selection of species?

2021-06. Tall towers
A tower is built by stacking rectangular bricks on top of each other. Some people argue that the maximum height of the tower is limited by the human skill to place the bricks gently; others may say that the limiting factor is non-perfect shape of the bricks. Perform experiments to outline the factors that limit the maximum height of such a tower.

2021-07. Electricity meters
Energy meters installed at your home have been measuring power usage for decades. Collect periodic readings for a sufficiently long period of time, e.g. last 20 years, and identify subtle or significant changes in energy using behavior at your home. When did your family switch from incandescent to fluorescent or LED bulbs? Is there a history of electric heating or air conditioning? Are there regular seasonal variations in power usage?

2021-08. When dumplings rise
Frozen dumplings sink in water. However, they rise to the surface when cooked in boiling water. Are the dumplings ready once they float? Investigate this effect.

2021-09. Salt and ice
Study the effectiveness of salt to melt ice cubes.

2021-10. Blurred text
Printed text is well visible if covered with a piece of transparent film. As the film is lifted, the text becomes blurred and may gradually disappear. What parameters of the film are relevant? Investigate this phenomenon.

2021-11. Oxygen from plants
Suggest an experimental method to measure how much oxygen is produced by a green plant.

2021-12. Zinc layers
If a copper coin and small granules of zinc are immersed into a solution of zinc sulphate and then heated, a layer of zinc appears on the coin. What is the thickness of the zinc layer? What other metals can be covered with zinc in such an experiment? Investigate and explain the effect.

2021-13. Invent Yourself: Skin conductance
Conductance of human skin is often dependent on psychological condition and emotional stimulation. Suggest an interesting problem requiring experimental measurements of respective parameters.

2021-14. Invent Yourself: Epidemiology
The human society has been profoundly affected by the COVID-19 pandemic. Propose a study involving analysis of available epidemiological data for the pandemic.

2021-15. Invent Yourself: Hearing range
There is a considerable variation in the range of frequencies that can be heard by humans and other mammals. Suggest a problem to investigate the lowest and highest audible frequencies for specific species of societal groups.

2021-16. Invent Yourself: Weak signals
Controlling signal-to-noise ratio is important in many measurements to distinguish a meaningful signal from statistical fluke. Propose a problem requiring experiments to detect very weak signals.

2021-17. Invent Yourself: Standing waves
Formulate a problem about an interesting experiment where standing waves are observed.