Questions and Answers on Natural Phenomena

[Grelinette]

Here is an interesting questionnaire that shows that certain phenomena have some surprising explanations.

The answers are at the end, but try to answer before going to see the answers.

(Questionnaire from the site http://www.prepa-cpe.com/quiz/ Integrated Preparatory Classes at the Higher School of Physics and Electronics Chemistry of Lyon)

Question 1
On a cold day, you place two identical containers containing the same volume of water on the floor, one at 50 ° C and the other at 95 ° C. In which container will the water freeze as quickly as possible?
1. Obviously, in the one that contains the water initially at 50 ° C.
2. It all depends on the outside temperature.
3. Experience shows that the one that contains the water at 95 ° C freezes first!

Question 2
Why do not clouds fall?
1. Because the water vapor constituting the clouds is lighter than the air.
2. Because the clouds are small water bubbles filled with water vapor.
3. The clouds are falling, but very slowly.
4. Clouds are only an immaterial reflection.

Question 3
Why does the Earth have an atmosphere while the moon does not have one?
1. It's a coincidence.
2. Since the constitution of the Earth and the Moon, it was so.
3. All that is received from the space remains trapped.
4. Gravity on the moon is too weak to hold gas molecules.

Question 4
The conjecture of Syracuse.
Let's start from an integer and then apply two rules:
- rule 1: if the number is odd, we multiply it by 3 and we add 1.
- rule 2: if the number is even, we divide it by 2.
Example: with the initial integer 5, we move to 16 with the 1 rule, then to 8 with the 2 rule, then to 4, then to 2, then to 1. And here we stop because 1 leads to 4, then 2, then again 1 ...

1. We finally get to 1 with 5, but it's a special case.
2. We always always end up with 1 with any starting integer and we can prove it by recurrence.
3. We always always come to 1 but we still do not know how to prove it.
4. Counterexamples can be found.

Question 5
Why do lakes freeze at the top?
1. Because of the mineral salts present in the soil.
2. Because of the density variation properties of water.
3. Because of the more fragile hydrogen bonds on the surface where the water mixes with the air.
4. Because of underwater currents.

Question 6
By plane, if you compare the times of flight back and forth, we realize that it is longer to fly from East to West rather than from West to East. Why ?
1. The cause is the rotation of the Earth in the West-East direction during the duration of the flight.
2. The durations are actually identical.
3. This is the time that does not flow in a uniform way.
4. The contrary winds are the cause.

Question 7
What is the main reason that the temperature is lower in altitude than at sea level?
1. The Earth receives solar radiation and heats the air layers closest to the ground. It acts as a gigantic radiator.
2. The air rises by expanding.
3. The closer we get to space, the closer we get to vacuum, so to a low temperature.
4. The air molecules slow down during their upward movement, which corresponds to a decrease in temperature.

Question 8
A child sitting in a boat floating in a pool throws a stone into the water. How is the water level changed in the pool?
1. The water level rises.
2. The water level drops.
3. The water level is not changed.
4. The result depends on how to throw the stone.

Question 9
Why can jams in jars last for a long time?
1. The high sugar concentration can explain it.
2. Potting when the jam is still very hot kills the bacteria.
3. By filling the pots to the brim, we remove any atmosphere and therefore any bacteria in the pot.
4. The cool temperature of the cellar prevents the proliferation of bacteria.

Question 10
A button must be able to be threaded into a buttonhole regardless of its orientation. To have this property of constant diameter whatever the orientation, does the button necessarily have to have a circular contour (disk)?
1. No, there are other shapes giving a constant diameter.
2. Yes of course
3. British coins at 7 sides in arcs of circles check this property.
4. If we measure the diameter of a cylinder with a caliper and always get the same value, it is circular.

Question 11
What causes the crack of a whip in the air?
1. Its end crosses the wall of sound.
2. The mechanical shock between two parts of ropes.
3. The vibration of the air moved.
4. In reality the whips do not make noise, it is only in the movies!

Question 12
Why is there a sensation of cold when you touch a metal object at 15 ° C that you do not have when you touch a piece of wood at 15 ° C?
1. This is false, in fact we have the same feeling in both cases.
2. Because the metal is smooth: it's not a real feeling of cold but we mentally associate the smooth and the cold.
3. Because metal is a better thermal conductor than the hand and absorbs heat quickly, not wood.
4. Because the wood has a lot of carbon that reacts chemically with the skin, which instantly warms the affected surface of the wood.


answers:
Q1: Answer: none
Experience does not conclude.
Explanation: Contrary to what one might think, it is water initially at 95 ° C that will freeze first. The main reason is the significant evaporation of the water at 95 ° C, which decreases the water mass to freeze.

Q2: Answer: 3
Explanation: Water vapor is lighter than air, but clouds are not composed of water vapor! This last is besides invisible and would give transparent clouds. Clouds are made up of tiny drops of water (or small ice crystals) that are denser than air but have a significant amount of friction in the air, which slows down their descent. The clouds fall so very slowly and an updraft can make them rise or stop their fall.

Q3: Answer: 4
Explanation: The air molecules in the Earth's atmosphere are subject to Earth's gravitational attraction in addition to their rapid agitations with collisions on other molecules and on the Earth's surface: they remain close to the Earth's surface. As for the moon, it exerts a force of gravitation too weak to retain its atmosphere, which has disappeared.

Q4: Answer: 3
Explanation: No counter-examples were found, and the demonstration that seems simple is not yet established!

Q5: Answer: 2
Explanation: The density of the liquid water goes through a maximum at 4 ° C. Thus, as the surface water cools, its density increases as it approaches 4 ° C. The water of the lower layers will then go up until all the lake is 4 °. From there, the water can begin to freeze on the surface and remain at 4 ° below (more dense water at depth).

Q6: Answer: 4
Explanation: The answer is not 1. In the terrestrial reference system, the plane will not move faster to the left or to the right because the Earth is moving. On the other hand, the winds that blow in the upper atmosphere still predominantly blow from West to East (direction of rotation of the Earth). So the East-West flight is against the wind, so usually a little slower.

Q7: Answer: 2
Explanation: Air rises to the upper layers of the atmosphere where atmospheric pressure is lower. The air relaxes and when a gas expands, it cools (this is what happens in a refrigerator when the heating fluid relaxes in the evaporator), hence the temperature drop in altitude.

Q8: Answer: 2
Explanation: When the stone is in the boat, its weight has the same value as the weight of the volume of water moved. As a stone is denser than water, the volume of water it moves is greater than its volume. When the stone is at the bottom of the pool, it moves a volume of water equal to its own volume. So the volume of water displaced when the stone is at the bottom of the pool is less than the volume of water moved when the stone is in the boat. Conclusion: the water level of the pool drops.

Q9: Answer: 1
Explanation: The high sugar concentration of jams causes the death of bacteria by the phenomenon of osmosis. The membrane of a cell such as a bacterium is semi-permeable. Water molecules pass from bacteria to jam and jam to bacteria. But more water comes out of the bacteria than it gets in: the water goes from the diluted solution (bacterium) to the concentrated solution (jam) according to the phenomenon of osmosis, until causing the death of the bacteria. Sugar, like salt with fish and meat, ensures preservation without refrigeration.

Q10: Answer: 1 and 3
Explanation: Let's give another form of constant diameter called Reuleaux triangle. To do this, let us construct an equilateral triangle and three equal arcs centered on the vertices of the equilateral triangle and radius equal to one of the sides of the triangle. If we measure the size of this figure with a caliper, we will always get the same size (equal to the side of the equilateral triangle). The case of coins in 3. is a saving of metal and these coins pass perfectly, like circular coins, in the slots of currency devices, whatever their orientation. Therefore, 4. is wrong.

Q11: Answer: 1
Explanation: All kinetic energy is transmitted from the gesture given to the handle, the last centimeters of the whip. With a gesture of 20 m / s initially, the end can reach more than 400 m / s, that is to say exceed the speed of sound, which produces a mini shock wave similar to that produced by a supersonic airplane.

Q12: Answer: 3
Explanation: The hand is a better thermal conductor than wood, but not as good as metal. By touching wood which is a bad heat conductor, the heat exchange between the hand and the wood is slow and the temperature felt is close to that of the hand. On the other hand, by touching a fairly large metal object that is a good thermal conductor, a quantity of heat passes quickly from the hand to the metal, hence the feeling of cold felt. The high thermal conductivity of the metal also explains why it is easier to burn yourself by touching a metal object.

[vinzman]

Thank you, I found that excellent and I copied it and put on my facebook!