Try to stand up

You'd think I was joking if I told you that you wouldn't be able to get up from a chair provided you sat on it in a certain way, even though you wouldn't be strapped down to it. Very well, let's have a go. Sit down on a chair in the same way the boy in Fig. 13 is sitting. Sit upright and don't shove your feet under the chair. Now try to get up without moving your feet or bending forward. You can't, however hard you try. You'll never stand up until you push your feet under the chair or lean forwards. Before I explain, let me tell you about the equilibrium of bodies in general, and of the human body in particular. A thing will not topple only when the perpendicular from its centre of gravity goes through its base. 







The leaning cylinder in Fig. 14 is bound to fall. If, on the other hand, the perpendicular from its centre of gravity fell through its base, it wouldn't topple over. The famous leaning towers of Pisa and Bologna, or the leaning campanile in Arkhangelsk (Fig. 15), don't fall, despite their tilt, for the same reason. The perpendiculars from their centres of gravity do not lie outside their bases. Another reason is that their foundations are sunk deep in the ground.


You won't fall only when the perpendicular from your centre of gravity lies within the area bound by the outer edge of your feet (Fig. 16). That is why it is so hard to stand on one leg and still harder to balance on a tight-rope. Our "base" is very small and the perpendicular from the centre of gravity may easily come to lie outside its limits.  Porters who carry loads on their heads are well-built a point, I presume, you have noticed. You may have also seen exquisite statues of women holding jars on their heads. It is because they carry a load on their heads that these people have to hold their heads and bodies upright. If they were to lean in any direction, this would shift the perpendicular from the centre of gravity higher than usual, because of the head-load, outside the base and unbalance them. 

Back now to the problem I set you at the beginning of the chapter. The sitting boy's centre of gravity is inside the body near the spine about 20 centimeters above the level of his navel. Drop a perpendicular from this point. It will pass through the chair behind the feet. You already know that for the man to stand up it should go through the area taken up by the feet. Consequently, when we get up we must either bend forward, to shift the centre of gravity, or shove our feet beneath the chair to place our "base" below.

Do Animals have language ?

All animals communicate. But do they have language? Michele Bishop details the four specific qualities we associate with language and investigates whether or not certain animals utilize some or all of those qualities to communicate.

Riddle: Find logical mistake in the sentence

Mary, in 1925, told her friend, "My husband died in World War I."

Riddle: Color of the bear

If you are sitting in a house with all windows facing south and there is a bear in the window, what is the color of the bear ?

Super heroes of metal world

The word "metal" means strength; but strength can be measured in different ways just like superheroes have different powers.

Malleability

Malleability is the ability of a metal to be hammered into thin sheets. Gold and silver are highly malleable. When a piece of hot iron is hammered it takes the shape of a sheet. The property is not seen in non-metals.

Silver is a transition metal. It has the highest electrical conductivity of any element and the highest thermal conductivity of any metal. The metal occurs naturally in its pure, free form, as an alloy with gold and other metals, and in minerals such as argentite and chlorargyrite. Most silver is produced as a byproduct of copper, gold, lead, and zinc refining. It has long been valued as a precious metal

Ductility/Tensile Strength
Ductility is a solid material's ability to deform when it is pulled from both ends; this is often characterized by the material's ability to be stretched into a wire. Again gold is one of the most ductile metals.

Gold - its a very soft and beautiful metal coveted for thousands of years chemical properties of gold.

Hardness
Hardness is a measure of how resistant solid matter is to various kinds of permanent shape change when a compressive force is applied.

Titanium is classified as a transitional metal. Titanium is the ninth most abundant element in Earth’s crust. It is almost always present in igneous rocks and their sediments. Pure titanium is a lustrous white metal. It is strong, light with low density, and has excellent corrosion resistance. Titanium is as strong as steel but 45 percent lighter. It is 60 percent heavier than aluminum, but twice as strong.

Toughness
The toughness of a material is the maximum amount of energy it can absorb before fracturing, which is different from the amount of force that can be applied.

Molybdenum is tough metal used in many types of power tools chemical properties of molybdenum.

Corrosion resistance
Corrosion is a process of gradual destruction of metal due to oxygen(process is called - oxidation). 

Zinc is a metallic chemical element. It is the 24th most abundant element in the Earth's crust and has five stable isotopes. Corrosion-resistant zinc plating of steel is the major application for zinc. Other applications are in batteries and alloys, such as brass

Shear strength
Shear strength represents how hard you can try to cut it without it breaking. When you cut a paper with scissors, the paper is failing in its shear strength.

iron is used to make an alloy called "steel" which has very high shear strength.