Helicopter tail rotor

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We know that helicopter should have a tail rotor to counteract the torque created due to the main rotor blades rotation.

There is a special thing about tail rotor too. For example see the picture, there are two sets of blades (2x2=4). One set has two blades in a line.

why two sets? why can't they put just a 4 blade rotor just like a fan in our room?

The tail rotor rotates with a very high speed. Obviously causes noise. To reduce this they will put two sets of blades which will cut off the noise created by the other set

Why do we YAWN ?

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we do yawn. But why do we yawn?

A theory says that when we sleep our body metabolic rates go down. so we need less oxygen. But when we feel sleepy or tired, this happens we take in less oxygen but our body metabolic rates are still high so our body automatically tries to take in more oxygen. This is through Yawn. This is an involuntary action.

Heavy metals

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How actually these are formed...?

It is assumed that universe has only Hydrogen initially. Because of high pressure and heat, these hydrogen atoms combine to form higher atomic elements. The temperature and pressure at the core of SUN is capable of producing Helium from Hydrogen atoms.

But on Earth we have very high atomic number elements like Titanium, Uranium etc. How come??

These are generated because of the intense pressure and temperature caused by BIG BANG.

Volcanoes

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After the big bang, few big pieces of explosions attracted the others nearby. As they came near and near, their velocities became high and it was like a collision of huge bodies. Guess how many must have collided. This energy produced from the collision was stored in the resulting planet which is EARTH, which melted the core and hence it remains as LAVA.

Pencil fact

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Ever thought why are we able to write with pencil but not a black plastic or some other material...?

Pencil is made of Graphite which is made of carbon atoms held in the form of layer structure as shown in the picture.


These layers can easily slip, slide over. So when we write we just force them to slip and stick to the paper.
:)

Walking the first step

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so what helps us in walking. One thing is certain to feel the gravity. You may not expect this but our ears are the main organs which helps us feel gravity so that we can walk (legs are a means to walk). The ears contain minute hair inside, which act as gravity sensors.


image courtesy - http://gethealthlife.blogspot.com/2009_09_01_archive.html

Water

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We can see through water when the depth is less. When the depth becomes huge, we cannot see through it. Because water absorbs light. Guess what it looks like in oceans ..???