150 years ago in 1851 a French scientist
named Leo Foucault after experimenting on Bob, revealed that the earth rotates
in its axis. Moreover he found out the value of the speed of this rotation. After
Foucault's experiments, Foucault pendulum in various length, was setup in a few
selected science museums and universities of the world. Among them Moscow University,
Yale University and Inter University Astrophysics Centre, Pune, are notable. The
Foucault pendulum set up in D.D.U. Gorakhpur University has the pride of being
the first among the sate universities.
Foucault pendulum is like other
ordinary pendulums but it is capable of pendulating freely from its support to
its axis, it was found in this experiment that Pendulum moves regularly with equal
speed clockwise and after a scheduled time interval T pendulum again begins to
pendulate at its starting place. If for any reason viz. friction of air, viscosity,
etc. pendulum energy is lessened, the bob will always make fascinating movement.
Time interval T is less than sine Ø from the periodic time of earth revolution
at its axis. The value of this time interval at the poles of earth will be 25
hours.
Pendulizing bob of 28 kg mass with the help of 70 mt. long wire
Foucault made them freely pendulate from the tower of famous church pantheon of
Paris. To exhibit practically the pendulation of the pendulum pins were annexed
with the balls which at every revolution noted it sign on the sand mound which
was arranged round the pendulums. Foucault found the value of periodic time from
the place of its revolution 32 hours.
Long ago from the experiment of
Foucault, Arya Bhatta, the Indian astrologer, in the 5th century had expressed
his conception of the earth's rotation at its axis. He had explained the fascinating
movement of the heavenly bodies in the sky in his famous book, Arya Bhatta. The
poem is as below.
As the man sailing by boat feels the things at the river
bank, going backwards, similarly stationary stars appears to us moving westward.
The astrologists of that era paid a deaf ear to the revolutionary conception
of Arya Bhatta, and took it for granted that earth is stationary. We know that
if two things are making relative in motion, then the man existing at one thing
finds himself stationary and the other moving. The sun's movement in the sky is
an example of the similar situation. The conception and their firmness about the
relative motion of the earth and the sun of Copernicus and Galileo are well known
to the world. The drop scene comes after such experiments.
If any mass
placed on any moving thing, moves, that pendulum will feel a force which besides
the velocity of the pendulum, will depend on the frequency of the product of the
velocity of the pendulum. Its direction is perpendicular to the velocity of the
mass and the velocity of the rotation of the thing. The velocity of then mass
placed on the poles of the earth is perpendicular to the velocity of the earth's
revolution. So that value of this force here is very high and is perpendicular
to the velocity of the mass. This effect was given by Gurtov Coriolis a French
engineer in 1829. So the above said velocity is named as Coriolis force. If any
mass from any place of a lower is freely dropped, with the effect of Coriolis
force, the mass will fall eastward instead of falling down. But the value of this
force is generally very less. For example a mass placed at the height of 300 mt.
At 40o latitude instead of falling down, will fall 9 cm. eastward. The effect
visible in the Foucault pendulum is the effect of Coriolis force.
The
university Foucault pendulum is being made by national science museum (N.C.S.M)
Kolkata. Its length is 35ft and its oscillating frequency 5ft. To make the revolution
effect visible, a path of 6 mt. Diameter well marked with degrees is placed at
the bottom of the pendulum. At Gorakhpur 26o, 25 latitude the periodic time of
rotation will be nearly 53 hours i.e. meridian 63/4 o per hour will be grow. Its
length is to be great to make the effect soon visible, because pendulums movements
will not simple harmonic if oscillating frequency is increased from its limit.
In the above context the setting up of Foucault pendulum in any university means
to make science universal and also make the students of science understand the
conception of Coriolis force easily.
