Science - Physics

How the Metric system started?
Metric system was invented in France in 1791. Since the change was started from measuring the length, that is why they chose the Latin word "Meter" which means "measurement". So the whole system of measurement was named as "Metric" system. Now, how long was the meter? In the beginning it was equal to Earth's circumference - 1/40,000,000. It was written on a rod and kept securely in a museum. Later, no relation could be established between these two. Because of its destruction in any given circumstances, that measurement was transferred to those natural measures which do not change. Since 1983, a meter's length is equal to the length which light crosses in 1/299,792,458 second - about three hundred millionth part of a second. Later on the basis of this measurement other measures were decided.

Different speeds?
A normal man walks 1.5 meter per second. Marching soldiers walk 2 meters per second. A fly's flying speed is more than the walking speed of man - 5 meters per second. On the other side, a snail walks only 1.5 mm in one second, and tortoise walks about 2 cm in one second. If you want to fly with cheel, you will have to take an aeroplane. Man-made rockets fly only 8 km per second.

Sea in which you cannot drown
There is a Dead Sea in Philistine in which a man cannot drown. Because it has so much minerals that its water is heavier than the normal sea water. Normal sea water has less than 4% minerals, while in this sea there are 24% or more minerals. That is why if somebody jumps in to it, he cannot drown.

How do you see the colors?
Color is those rays of the light which our eyes can see. And colors can be seen only in the light. Where there is no light, there is no color. You see only those colors which are not absorbed by the surface of the object.

Why the sky is red at sunrise and sunset?
Red color spreads in the sky at the time of sunset. It looks beautiful. But it is not because that the Sun is red. If you see the Sun, the Sun is not red. At this time these colors spread because of the distance through which the Sun rays have to go through. As much the Sun will be down, the same distance the rays will have to travel through atmosphere. Violet, blue and green colors are not absorbed by the atmosphere while red color is more unabsorbed - about ten times, and red and yellow colors are decreased too, that is why only red and yellow colors are seen in the sky.

H. G. Wells has written in one of his novels that a bullet went up to 70 km and came back in a few minutes. HOW?

What will happen if a well is dug through the Earth, and you travel through that well? 
Since there is no bottom of the well, you will be safe. You will not stop in the center of the Earth too, because when you will reach near it your speed will increase (gravitation will decrease when you reach the center of the Earth) - about 8 km per second, and you will continue to fall until you come out of the well on the other side of the Earth. Now after reaching on the other end, if you do not hold something tightly, you will again start falling with a hop. A both-way journey will take only 1 and 1/2 hours. (On the center of the Earth weight decreases, because gravitation works around the object not below the object

Try this
You sit on a chair, with straight back and legs with 90 degree angle on the ground. Now you try to get up without bending, you cannot get up. Because you can only get up when your feet or back are not at 90 degree angle. This means a thing cannot turn till it is making a 90 degree angle line reaching up from its base. that is why the Pissa Leaning Tower is not falling down.

No two snowflakes are same
Do you know that no two snow flakes are same in design and they are white, not colorless. Sometimes one snow flake can be of 3 cm diameter. In fact its size depends on temperature, if temperature is low then flake size will also be small.

City in the sky
What is mirage? A thirsty man sees water in the desert, on a warm day as you reach near the hill it seems that the road is wet, even in the sea you see ships in the sky. These are the examples of mirage. The most famous mirage is in Mesina in Sicily. The whole Mesina city is reflected in sky and forts flying slowly in the air.

Blue hills
Distant green hills seem to look blue, why? Many kinds of particles - dust, ash, smoke etc., swim in the air. When sunlight falls on them then different colors of light refract from them. Blue and violet colors are of more temperature, so they refract more than the green, yellow and red which are of low temperature, that is why hills look blue.

Water boils at low temperature on hills, why?
As much higher we go, the temperature goes down, so the water will also boil at as much lower temperature.

How much high temperature a man can tolerate?
Whatever you think, a human being can tolerate more than that heat. It is found that in the cabins of travelers traveling in the Bay of Iran, temperature reaches up to 50 degree C. The highest temperature in the world has been recorded in the Death Valley of California - 56 degree C. It is found by experiment, that in dry air, a man can tolerate 160 degree C temperature - temperature more than the boiling water.

Ice takes more space than water
Normally things shrink when get cold, but surprisingly water expands when frozen. How much rate? It is 10%. So if you are freezing 9 quart water, it will convert into 10 quart ice. On one side, this technique can burst water pipes, on the other side it is used to break rocks in mines. And because ice is lighter than the water, it floats. So in rivers etc. when upper layer of the water is frozen, the lower part is still liquid and fish can live there easily, or on the other hand, you think that you can skate on that ice but as you go on the ice, the ice breaks and you fall down in the cold chilly water.

Why the red color light used for STOP signs?
Red color light can be seen from a long distance, while blue, green or violet light cannot be seen so far. Because when light passes through the glass, whichever color has longest wavelength refract the least and whichever color has the shortest wavelength refract most. That is why red color is used in rail signals. even in fog and storms red color rays refract least and that is why can be seen from a long distance, while blue, green and violet cannot.

Does the Sun change its color?
Why the Sun looks yellow color at the time of sunrise and sunset? Although all seven colors start from the Sun, but in the atmosphere blue and violet color rays refract more and red and yellow color rays less. That is why red and yellow colors dominate and sun looks more  yellow. Since at the time sun rise and sunset the rays have to pass a long distance, yellow color rays refract more and leaving the red color and all other color rays in the atmosphere.

See the blue ink letters black
If you see the blue ink letters with red color glasses they will look black. Why? Because only red rays can pass through red glass, not the blue ones. and since there is no light there, in the absence of the light blue letters look black.

Rainbow's colors
Rainbow has seven colors in it - violet, sky blue, blue, green, yellow, orange and red. When you see a rainbow you will find the violet color at the lowest and red color at the top, because red color refract the most. To appear this, the sun, the spectator's eyes and the curved part of the rainbow should be in one straight line. This does not usually happen in mid day, it is either in the morning or afternoon. Morning rainbow forecasts rain in west and the sun in east, and afternoon rainbow means rain in east and the sun in west.

Why the sky is red before storm comes?
You must have seen the sky red before any storm comes. What happens at that time, that before the storm, dust particles fill the lower sky. These particles refract the lights of the city and the longest wavelength color red spreads out. But this happens only when the atmosphere is dry. After the rainfall it does not happen so.

How cold is at 10,000 meter height?
You can calculate that how cold it will be at 10,000 meter high place. The formula is: 2 degree C temperature falls at every 300 meter height.

Make any object invisible
When some object does not refract any color of light and absorb it fully then that object becomes invisible.

Magnet does not attract only iron
Do you know that magnet does not attract only iron? It attracts some other metals too, like aluminum, nickel, cobalt, manganese, while some metals distract from the magnet like zinc, bismeth etc. Besides, magnet does not attract very hot iron.

Speed of sound
In the atmosphere, speed of the sound is 335 meter per second at 0 degree C. But if temperature rises, then the speed of the sound also rises. Inside water, sound travels faster. In 8 degree C temperature water, sound travels at the speed of 1435 meter per second. Thus sound speed depends on the medium in which it travels.