What is a Orbital Velocity?

Orbital velocity is the least velocity which should be given to any object or satellite so that it moves in its orbit.It is basically a minimum velocity given to any object so that it moves in a circular path.
If,
m= mass of the object.
R+h=height of the object or satellite.
M= mass of the earth.
v= orbital velocity.
then we know that when any object moves in a circular path there should be some forces which can provide the cetripetal force.In this case that force will be provided by the gravitational force between the earth and the object.

so,
centripetal force=gravitaional force between the earth and that object

mv^2/R+h=GMm/(R+h)^2
v^2=GM/R+h..............................1
we also know ,
mg=GMm/(R+h)^2.............................2

therefore from 1 and 2 .
v^2=g(R+h).

also from 1 we get that orbital velocity depends on its mass and its height from the earth.

Concept of Deja Vu

Deja Vu is a feeling that a particular event taking place in the present had happened in the past or had been repeated . Surveys have revealed that as much as 70% of the population have had these experiences, usually between ages 15 to 25, when the mind is still subject to noticing the change in environment.The experience is usually related to a very ordinary event, but it is so striking that it is remembered for several years afterwards.

CONCEPT:a brain consists of two parts 1)short term memory part

2)long term memory part


Short term memory part stores event occuring in the presentlong term memory part stores memory occured in the pastso while experiencing deja vu , events occuring in the present are stored in the long term memory part of the brain before the short term memory part even recieves the information and processes it and there is a fraction of second difference.So the person feels that the event in the present had happened in the past

What is a BIG BANG?

The Big Bang Theory is the dominant scientific theory about the origin of the universe. According to the big bang, the universe was created sometime between 10 billion and 20 billion years ago from a cosmic explosion that hurled matter and in all directions.
In 1927, the Belgian priest Georges Lemaître was the first to propose that the universe began with the explosion of a primeval atom. His proposal came after observing the red shift in distant nebulas by astronomers to a model of the universe based on relativity. Years later, Edwin Hubble found experimental evidence to help justify Lemaître's theory. He found that distant galaxies in every direction are going away from us with speeds proportional to their distance.
The big bang was initially suggested because it explains why distant galaxies are traveling away from us at great speeds. The theory also predicts the existence of cosmic background radiation (the glow left over from the explosion itself). The Big Bang Theory received its strongest confirmation when this radiation was discovered in 1964 by Arno Penzias and Robert Wilson, who later won the Nobel Prize for this discovery.
Although the Big Bang Theory is widely accepted, it probably will never be proved; consequentially, leaving a number of tough, unanswered questions.

concept of black hole

we know from gavitaional law that force of gravity is given by,

g=GM/R^2
so if we go on decrease the radius keeping the mass constant then force of gravity goes on increasing.If we take radius of an object of mass M to be zero then force of gravity becomes infinite.Its gavitational force becomes so high that even light cannot exist there so it appears black. So a black hole can be considered as a region of empty space with a point like singularity at the center and an event horizon at the outer edge . Research on this subject indicates that, rather than holding captured matter forever, black holes may slowly leak a form of thermal radiation.