Panta
rei - 'everything is changing'. Heraclitus lived
from 536 to 470 bc and is a well-known ancient philosopher.
He captured his philosophy in just two words: panta
rei, literally everything flows, or everything
is changing. Heraclitus argued that everything is
constantly changing, from the smallest grain
of sand to the stars in the sky. Only change itself
is real, every object ultimately is a figment of people's
imagination.
Foucault, Jean Bernard Léon , 1819–68, French physicist.
Known especially for his research on the speed of light, he determined
its velocity in air and found that its speed in water and other
media diminished in proportion to the index of refraction. He
originated the Foucault pendulum, with which he demonstrated
the earth's rotation. He also improved astronomical instruments,
especially the telescope; invented (1852) the gyroscope; and
investigated the eddy current (known also as the Foucault
current), an electric current induced in metal by a moving magnetic
field. With Armand Fizeau he took the first clear photograph
of the sun. From 1855 he was physicist at the Paris Observatory.
Foucault's Pendulum: In the Universe everything moves: the stars,
planets, moons. Everything on Earth moves as well, even though we may
not aware of this motion. A building might appear stationary to the observer
but we know that it is in fact moving at the speed of 1,000 miles an
hour around the center of the Earth. No place in space can be used as
a fixed reference point.
In 1848, Jean Bernard Foucault experimented with a large pendulum and
discovered that when it swings, the Earth appears to move 'under' it.
In this way Foucault's pendulum proves that the Earth rotates.
The pendulum consisted simply of a large weight suspended by a long cable
to a ceiling several stories high. For this pendulum there exists a slow
rotation of the plane of oscillation which was evidence Foucault needed
to prove the Earth's rotation.
It is based on a concept that Isaac Newton discovered. When a body is
set in motion it will move continuously in a straight line from its origin,
provided no outside forces alter the direction. When Foucault's Pendulum
is set in motion it therefore must swing or oscillate in continuously
the same direction. The amazing thing is that the direction is universally
fixed. If the pendulum is started swinging toward a specific star, it's
direction will remain pointed toward that the star until acted on by
an outside force. The direction the pendulum is swinging becomes a matter
of perspective.
The first amazing property of Foucault's
pendulum is that if it is set in motion in the Northern Hemisphere, the
line the pendulum traces out is always shifted toward the right. The
opposite holds for the Southern Hemisphere. The pendulum motion will
be shifted toward the left. In fact as the pendulum eventually traces
out a circle. The plane being fixed means that the rotation of the plane
of oscillation is the result of the Earth rotating in this plane. It
seems at first glance there is a force
acting on the pendulum however this is just the pseudo force we call
the Coriolos force.
Something which contradicts our intuitive notion of the Coriolos force
and hence the motion of the Foucault Pendulum is that the direction in
which the pendulum is initially started has no bearing on how much the
pendulum's motion seems to shift. We would expected that the motion would
be shifted the most when the direction of oscillation is North to South
but this is not so.
The second amazing property of Foucault's
pendulum is the fact that the period of rotation of the plane of oscillation,
or in other words the time it takes to trace back to its original position
from when it was released, is not a constant. Again, intuition suggests that
the Pendulum no matter where on the surface of the Earth would be in
the same place in 24 hours, well it isn't. The period of rotation is
directly related to the latitude at which the pendulum is swinging.
How does Foucault's pendulum show that the Earth is spinning?
Foucault first suggested that if you swung a large pendulum all day,
starting it swinging north-south, its swing would change to east-west.
Why should this be? If we stood at the center of a rotating, circular
stage and we walked to the perimeter, we would feel a force pushing us
aside. This is because the circumference of the disc is traveling faster
than the center. By walking outwards we are speeding up and for every
acceleration there is a force. People on the equator are spinning quicker
than those on the pole. So, if we walk South towards the equator, we
are increasing our speed and will feel a force. Walking towards the pole
we experience a deceleration and another force. The swings of Foucault's
pendulum mean it experiences tiny forces because it has a different speed
at the North end of a swing than at the South. This tiny
force is sufficient, over a long period of time, to change the direction
of the swing. None of this would happen if the Earth didn't spin.
An eclipse changes the movement of the pendulum.
In a marathon experiment, Maurice Allais released a Foucault pendulum
every 14 minutes - for 30 days and nights -without missing a data point.
He recorded the direction of rotation (in degrees) at his Paris laboratory.
This energetic show of human endurance happened to overlap with the 1954
solar eclipse. During the eclipse, the pendulum took an unexpected turn,
changing its angle of rotation by 13.5 degrees.
Maurice Allais (1911 - ) won the Nobel Prize in Economics in 1988. He
stated, "All my researches in theoretical and applied physics which,
at first sight, appear to be remote from my main activity as an economist,
have, in reality, enriched me with valuable
experience."
Both before and after the eclipse, the pendulum experienced normal rotation
(Foucault effect of 0.19 degrees/minute). This 13.5-degree excursion
in the angular plane persisted throughout the length of the eclipse,
a total of 2.5 hours of observations. Allais got similar results when
he later repeated the experiment during a solar eclipse in 1959.
Panta
rei - 'everything is changing'. Heraclitus lived
from 536 to 470 bc and is a well-known ancient philosopher.
He captured his philosophy in just two words: panta
rei, literally everything flows, or everything
is changing. Heraclitus argued that everything is
constantly changing, from the smallest grain
of sand to the stars in the sky. Only change itself
is real, every object ultimately is a figment of people's
imagination.
Foucault
current), an electric current induced in metal by a moving magnetic
field. With Armand Fizeau he took the first clear photograph
of the sun. From 1855 he was physicist at the Paris Observatory.
force
acting on the pendulum however this is just the pseudo force we call
the Coriolos force. 
that
the Pendulum no matter where on the surface of the Earth would be in
the same place in 24 hours, well it isn't. The period of rotation is
directly related to the latitude at which the pendulum is swinging. 
tiny
force is sufficient, over a long period of time, to change the direction
of the swing. None of this would happen if the Earth didn't spin.
valuable
experience."