Zadania 1998 (ang)

1. Invent yourself
Construct an aeroplane from a sheet of paper (A4, 80 g/m2). Make it fly as far and/or as long as possible. Explain why it was impossible to reach a greater distance or a longer time.

2. Popping body
A body is submerged in water. After release it will pop out of the water. How does the height of the pop above the water surface depend on the initial conditions (depth and other parameters)?

3. Spinning disc
Investigate and explain the phenomenon of spinning annular disc as they progress down a straight, cylindrical rod. If the rod is moved upwards at a defined velocity, the disc spins at constant height. Investigate the mechanism.

4. Water streams
A can with three holes in the side-wall at the same height slightly above the bottom is filled with water. The water will escape in three separate streams. By gently touching the streams with a finger they may unite. Investigate the conditions for this to happen.

5. Water jet
If a vertical water jet falls down onto a horizontal plate, standing waves will develop on the surface of the jet. Investigate the dependence of this phenomenon on different parameters.

6. Mount Everest
Can you see Mount Everest from Darjeeling?

7. Air bubble
An air bubble rises in a water-filled, vertical tube with inner diameter 3 to 5 mm. How does the velocity of the rising bubble depend on its shape and size?

8. Trick
It is known that a glass filled with water and covered with a sheet of paper may be turned upside down without any loss of water. Find the minimum amount of water to perform the trick successfully.

9. Woven textiles
Look at a point-like light source through different woven textiles. Describe what you see. What is the explanation of the phenomenon?

10. Repeated freezing
While a vessel filled with an aqueous solution of a volatile fluid, e.g., ammonia, ethanol or acetone, is being cooled, repeated freezing and melting may be observed near the surface. Describe and explain the phenomenon.

11. Current system
In a Petri dish (shallow bowl), small metal balls, e.g., 2 mm in diameter, are immersed in a layer of castor oil. The inner rim of the dish contains an earthed metal ring. Above the centre of the dish there is a metal needle which does not touch the oil surface. Investigate what happens when the voltage between needle and earth is about 20 kV. Warning: The high voltage should be obtained by means of a safe generator, e.g., an electrostatic generator!

12. Powder conductivity
Measure and explain the conductivity of a mixture of metallic and dielectric powders with various proportions of the two components.

13. Rope
How is it possible that a very long and strong rope can be produced from short fibers? Prepare a rope from fibers and investigate its tensile strength.

14. Water rise
Immerse the end of a textile strip in water. How fast does the water rise in the strip and what height does it reach? In which way do these results depend on the properties of the textile?

15. Luminescent sugar
Investigate and explain the light produced when sugar crystals are pulverized. Are there other substances with the same property?

16. Strange motion
Make a mixture of ammonium nitrate and water, proportion 5 to 1. When the mixture is heated to about 100 °C it melts. When it cools, it crystallizes and you may observe a strange motion below the surface. Investigate and explain the phenomenon. Safety rules: Do not heat the ammonium nitrate without water, preferably use a water bath! Use protection glasses during the experiment!

17. Icicles
Investigate and explain the formation of icicles.