Progress ticks on with Time Concepts of Engineering and Technology Progress ticks on with Time Copyright © Texas Education Agency, 2012. All rights reserved.

Copyright © Texas Education Agency, 2012. All rights reserved. Clocks Close-up: Shadow Clock The shadow clock should have been really called a shadow watch.  It could fit in a pocket and was easy to carry around.  These shadow clocks were used in eighth century BC.  In the morning, the clock's crossbar must face the east and it must be turned around in the afternoon.  The shadow clock was a predecessor to the sundial.   You can learn how to make your own shadow clock. Copyright © Texas Education Agency, 2012. All rights reserved.

Copyright © Texas Education Agency, 2012. All rights reserved. Sundials (gnomom) The Egyptians thought they were the first to invent the shadow clock, but they were mistaken.  At the same time, the Chinese, Babylonians, Greeks and the Romans were using instruments to tell time.  The technical name for a shadow stick is gnomon,(NO mon) which is Greek for "the one that knows". Copyright © Texas Education Agency, 2012. All rights reserved.

Copyright © Texas Education Agency, 2012. All rights reserved. Obelisk The ancient Egyptians built tall stone towers called obelisks. Everybody could tell the time by looking at the obelisk's shadow. Obelisks were sometimes called "Cleopatra's Needles". Copyright © Texas Education Agency, 2012. All rights reserved.

Copyright © Texas Education Agency, 2012. All rights reserved. Prince Amenemhet made the king a clepsydra or a water clock.  He took a big bucket of water, filled it with water up to a specific line.  He then cut a small hole in the bottom of the bucket and marked off lines on the bucket after each hour had passed.  Copyright © Texas Education Agency, 2012. All rights reserved.

Copyright © Texas Education Agency, 2012. All rights reserved. Hourglass There were, of course, some problems with this water clock as well.  Water would flow more slowly or quickly when the temperature changed.  This is where sand came into effect.  The inventor of the sand clock is unknown but the sand clock or hourglass was commonly used in ancient times and is still used today.  They are often found in board games or are used as kitchen timers.  Is there an hourglass in your home? Copyright © Texas Education Agency, 2012. All rights reserved.

Copyright © Texas Education Agency, 2012. All rights reserved. The first mechanical clocks had a weight that slowly lowered moving gears which moved a hand and showed the hour.  They could only be built in tall towers because the weights needed to fall a great distance or else the clocks would only work for a short amount of time. People were amazed that these clocks were only off by about 2 hours a day.  Copyright © Texas Education Agency, 2012. All rights reserved.

Copyright © Texas Education Agency, 2012. All rights reserved. Pendulum-clock In 1656, Christiaan Huygens, a Dutch scientist, made the first pendulum clock, regulated by a mechanism with a "natural" period of oscillation. (Galileo Galilei is credited with inventing the pendulum-clock concept, and he studied the motion of the pendulum as early as 1582. He even sketched out a design for a pendulum clock, but he never actually constructed one before his death in 1642.) Huygen’s early pendulum clock had an error of less than 1 minute a day, the first time such accuracy had been achieved. His later refinements reduced his clock's error to less than 10 seconds a day. Galileo Galilei was born in Pisa, Italy on February 15, 1564. He was the oldest of seven children. His father was a musician and wool trader who wanted his son to study medicine as there was more money in medicine. At age eleven, Galileo was sent off to study in a Jesuit monastery. Copyright © Texas Education Agency, 2012. All rights reserved.

Copyright © Texas Education Agency, 2012. All rights reserved. Evolving technology In 1721, George Graham improved the pendulum clock's accuracy to 1 second per day by compensating for changes in the pendulum's length due to temperature variations. John Harrison, a carpenter and self-taught clock-maker, refined Graham's temperature compensation techniques and developed new methods for reducing friction. By 1761, he had built a marine chronometer with a spring and balance wheel escapement that won the British government's 1714 prize (worth more than $10,000,000 in today's currency) for a means of determining longitude to within one-half degree after a voyage to the West Indies. It kept time on board a rolling ship to about one-fifth of a second a day, nearly as well as a pendulum clock could do on land, and 10 times better than required to win the prize. Copyright © Texas Education Agency, 2012. All rights reserved.

Evolving technology continuing Over the next century, refinements led to Siegmund Riefler's clock with a nearly free pendulum in 1889, attaining an accuracy of a hundredth of a second a day and becoming the standard in many astronomical observatories. A true free-pendulum principle was introduced by R.J. Rudd about 1898, stimulating development of several free-pendulum clocks. One of the most famous, the W.H. Shortt clock, was demonstrated in 1921. The Shortt clock almost immediately replaced Riefler's clock as a supreme timekeeper in many observatories. This clock contained two pendulums, one a slave and the other a master. The slave pendulum gave the master pendulum the gentle pushes needed to maintain its motion, and also drove the clock's hands. This allowed the master pendulum to remain free from mechanical tasks that would disturb its regularity. Copyright © Texas Education Agency, 2012. All rights reserved.

Evolution of mechanical clocks Around 1675, Huygens developed the balance wheel and spring assembly, still found in some of today's wristwatches. This improvement allowed portable 17th century watches to keep time to 10 minutes a day. And in London in 1671, William Clement began building clocks with the new "anchor" or "recoil" escapement, a substantial improvement because it interferes less with the motion of the pendulum. Copyright © Texas Education Agency, 2012. All rights reserved.

Copyright © Texas Education Agency, 2012. All rights reserved. Quartz Clocks Quartz Clocks The performance of the Shortt clock was overtaken as quartz crystal oscillators and clocks, developed in the 1920s and onward, eventually improved timekeeping performance far beyond that achieved using pendulum and balance-wheel escapements. Copyright © Texas Education Agency, 2012. All rights reserved.

Copyright © Texas Education Agency, 2012. All rights reserved. Atomic clock Half way through the 20th century, atomic clocks were built that would only be off by one second every 30 million years. Atomic clock for your home: FOCS 1, a continuous cold caesium fountain atomic clock in Switzerland, started operating in 2004 at an uncertainty of one second in 30 million years Copyright © Texas Education Agency, 2012. All rights reserved.

Copyright © Texas Education Agency, 2012. All rights reserved. Clocks of today Clocks for the past 40 years have come in all kinds of shapes and sizes. Copyright © Texas Education Agency, 2012. All rights reserved.

Future of clocks today and tomorrow. Yes we will always have clock We now see them on cell phones Alarm clock Copyright © Texas Education Agency, 2012. All rights reserved.

How theY have affected society They have improved our lives by being able to coordinate our communication. One of the ethical problems with clocks is price we must pay. Is it ethical to sell a watch for $5,000 dollars when it only cost you $100 to make? Sometimes clock/watchmakers use materials that could be harmful to your skin. Does the expense of a watch make you more apt to be a crime victim if you are in the wrong place? Copyright © Texas Education Agency, 2012. All rights reserved.

Copyright © Texas Education Agency, 2012. All rights reserved. REFERENCES http://library.thinkquest.org/C008179/historical/basichistory.html http://physics.nist.gov/GenInt/Time/atomic.html http://en.wikipedia.org/wiki/Sundial http://www.fotosearch.com/DGT157/bld0097/ http://en.wikipedia.org/wiki/Hourglass http://www.uh.edu/engines/epi1506.htm http://inventors.about.com/od/gstartinventors/a/Galileo_Galilei.htm http://en.wikipedia.org/wiki/Pendulum_clock http://en.wikipedia.org/wiki/Quartz_clock http://www.abbeyclock.com/quartz.html Copyright © Texas Education Agency, 2012. All rights reserved.