Pendulum

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Pendulum

• 82 ???83???
• 86 ??? 89???

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Pendulum

• A gravity pendulum is a weight on the end of a
  rigid or flexible line or rod, which, when given
  some initial lift from the vertical position,
  will swing back and forth under the influence of
  gravity over its central (lowest) point.
• A torsion pendulum consists of a body suspended
  by a fine wire or elastic fiber in such a way
  that it executes rotational oscillations as the
  suspending wire or fiber twists and untwists.

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Galileo Galilei

• "The legend of how Galileo discovered this
  property of the simple pendulum is apocryphal,
  but neither the fact that he found it nor the
  profound effects that it had on our civilization
  can be denied.
• 1.Telescope
• 2.Pendulum

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Contribution

• In 1637, Galileo demonstrated the first pendulum
  as a controller for clock
• Control by gravity
• Pendulum has a natural frequency that is
  independent of amplitude and weight of the bob
• Its frequency is related only to length of the
  pendulum and acceleration of gravity.

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Telescope

• Complete the task of Hipparchos which is to use
  planet as timekeeper.
• -- use the four moons of Jupiter, with the added
  advantage that the eclipse occurs once or twice
  every night.
• Disadvantages
• --telescope is impossible to use at sea.
• --the eclipses were not quite instantaneous.

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Pendulum

• the second contribution to longitude story, and a
  significant contribution to horology
• 1484 Bernard Walther measure the interval between
  the rising of the planet Mercury and moment of
  sunrise.
• Tycho Brahe purchased and tried four clocks
  during 1577 and 1581 before concluding that the
  inherent defects of sixteenth century clockwork
  were too great for astronomical purposes.

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Galileos first pendulum

• At the age of 19 when Galileo was at a church and
  observed a chandelier swinging.
  
• 
  suspension light
• He timed the length of the pendulum's swing,
  or oscillation, with his pulse and made an
  interesting discovery.

No matter how far the chandelier swung, the
length of time it took for one oscillation was
always the same.
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Pendulum

• Isochronism
• Period T2?
• Associated with length, not with gravity
• It is isochronism that cause horology development

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Pendulum clock

• Invented by Galileo Galilei and his son,
  Vicenzio.
• First patented by Christiaan Huygens in 1657.
• Pendulum clocks have several parts
• Pendulums are made to not vary in length when the
  temperature changes.
• Solution --John Harrison invented the grid
  pendulum, which used the differential expansion
  of brass and steel to achieve a zero-expansion
  pendulum.
• Pendulums are frequently polished and streamlined
  to reduce the randomizing effects of turbulent
  air flow on the clock's accuracy.
• Solution--In the late 19th century and early 20th
  century, pendulums for clocks in astronomical
  observatories were often operated in a vacuum to
  make the pendulum's operation even more accurate.

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Christina Huygens

• in 1657, invented the first weight-driven clock
  with a pendulum

Make string oscillating along with the same
cycloid To reduce error
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John Harrison(1693-1776)

• He was given a watch when he was six to amuse him
  while in bed with smallpox, spending hours
  listening to it and studying its moving parts
• Developed the gridiron pendulum, consisting of
  alternating brass and steel rods assembled so
  that the different expansion and contraction
  rates cancelled each other out.
• The grasshopper escapement -- a control device
  for the step-by-step release of a clock's driving
  power.

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Gridiron pendulum

• The gridiron pendulum was an improvement of
  clocks developed by John Harrison, consisting of
  alternating brass and steel rods assembled so
  that the different expansion and contraction
  rates cancelled each other out.
• Any downward expansion of the suspended steel is
  counteracted by the upward expansion of the
  supporting brass. The adjustable pin connection
  was designed to make minute alterations to the
  length, in the field.

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Spring-driven clocks (Early 15th century, Europe)

• Spring-driven clocks brought timekeepers out of
  towers and into the home. In contrast to their
  weight-driven predecessors, spring-driven clocks
  are small and portable.
• Lead to the development of the first watch in the
  15th century.

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Mechanical clock (c,1270s, probably Europe)

• the driven weight is suspended from a cord wound
  around the main gear shaft, or barrel. As gravity
  pulls the weight down, the barrel turns, thus
  driving the escape wheel.
• In a typical verge-and-foliot escapement, the
  weighted rope unwind from the barrel, turning the
  toothed escape wheel.
• Escapement stabilize the power of gravitational
  force.

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Pendulum clock(1656, Dutch astronomer Christian
Huygens)

• In the early 1580s, Galileo observed that a given
  pendulum took the same amount of time to swing
  completely through a wide arc as it did a small
  arc.
• 1656 Huygens combined pendulum with a particular
  kind of escapement.
• Weight-driven Spring-driven
• In 1906, the first pendulum clock driven by a
  self contained battery started ticking.

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H1(1730-1735)

• a portable version.
• It is spring-driven and only runs for one day.
• The moving parts are controlled and
  counterbalanced by springs so that, H1 is
  independent of the direction of gravity.
•  It ensures that any change in motion which
  affects one of the balances is compensated for by
  the same effect on the other balance.

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H2(1737-1740)

• Fundamentally the same design as H1.
• Harrison began work on H2 in 1737 but in 1740
  realised its design was wrong.
• The bar balances did not always counter the
  motion of a ship, a deficiency that could be
  corrected if the balances were circular.
• Harrison requested more money from the Board to
  work on a third timekeeper...

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H3(1740-1759)

• After 19 years of labour, it failed to reach the
  accuracy required by the Board of Longitude
• H3 incorporated two inventions of Harrison's a
  bimetallic strip, to compensate the balance
  spring for the effects of changes in temperature,
  and the caged roller bearing, the ultimate
  version of his anti-friction devices.
• the solution to the longitude problem lay in an
  entirely different design.

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In the end of our report, we would like to share
with you

• Weep no more , no sigh , nor groan. Sorrow calls
  no time that's gone
• The time of life is short to spend that
  shortness basely, it would be too long .
• Do you love life ? Then do not squander time
  for that's the stuff life is made of .

The End