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The Beginning of Time
The Egyptians were the first
people who created a twenty-four hour day. Time was a little bit different in those
days. The night was divided up into twelve hours, which were designated by the
position of stars in the sky. The day was divided into ten hours and a shadow
clock was used to keep track of these hours. The twilight hours were the hours
before dawn and after sunset.
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. Sundials
were used in some of these groups, not because they work better, just because that's how
they decided to tell time.
After a while,
the Egyptians and other ancient societies realized that the sun rose and set in different
places in the summer and winter. In fact, the sun never took the same course on any
one day throughout the year! They tried everything, until they realized that if they
would just put the post of the sundial in at a special angle, it would work all year.
The major fault with sundials
and shadow clocks is obvious...They don't work at night! Amenophis I, the king of
Egypt, wanted to know what time it was all through the night without having to check the
position of the stars. As you can imagine, it would be inconvenient to get up and
out of bed every time you want to know the time. So, 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.
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?
The first mechanical
clocks had a weight that would slowly lower, moving gears which moved a hand which
showed the hour. They could only be build 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 about 2 hours a day. Think
if our clocks today were off by that much? If we were 2 hours late for school, we
could blame it on the clock.
While these clocks were inaccurate long
ago, some of them were created with such care that they still work today. In
Normandy, France, a big clock exists that was built in 1389. In Salisbury, England
you can see the oldest clock in the world, built in 1386. Today, cuckoo clocks are
still built using a weight-dropping mechanism.
Galileo
made an amazing contribution to the world of time, simply by not paying attention in
church. The year was 1581 and Galileo was 17. He was standing in the Cathedral
of Pisa watching the huge chandelier swinging back and forth from the ceiling of the
cathedral. Galileo noticed that no matter how short or long the arc of the
chandelier was, it took exactly the same amount of time to complete a full swing.
The chandelier gave Galileo the
idea to create a pendulum
clock. While the clock would eventually run of energy, it would keep accurate
time until the pendulum stopped. If the pendulum was set swinging again before it
stopped, there would never be a loss in accuracy. Because of this, pendulums caught
on and are still widely used today. Can you imagine making such a big discovery?
When
sailors sailed across the ocean, they could only tell their position using two
methods. When they were traveling from North to South, they could tell their
position using Polaris, the North Star. But, when they were traveling from East to
West, they ran into a problem. Pendulum clocks couldn't be used because the
pendulums were highly sensitive and could be easily shaken, making the clocks inaccurate.
In 1707, a British fleet crashed into the Scilly Islands, killing two thousand
soldiers and destroying four ships. Seven years late, the British government offered
twenty thousand pounds to whoever built a clock that would keep accurate time at sea.
This clock would have to be accurate to the second, so as to avoid another
unfortunate accident.
John Harrison, a carpenter,
was the winner of the contest. In 1728, John heard about the contest and began work
on a solution. Thirty-three years and three enormous clocks, John's small fourth
clock was tested. When the testing crew arrived in Jamaica 161 days later, the clock
was only five seconds off. John Harrison collected his prize money at the age of
seventy-nine.
Since
1761, timekeeping has significantly changed. In 1900, pendulum clocks had been
finely tuned so as to only be off by 1/100 of a second each day. In the '20s,
scientists discovered quartz crystals could keep even more accurate time than a pendulum
and were only off about 1/500 of a second each year. Half way through the 20th
century, atomic
clocks were built that would only be off by one second every 300 million years.
Who really needs a clock that accurate?
It is evident that times have
certainly changed. Clocks have made major leaps and bounds since the days of the
shadow clock. Now we have accurate, reliable clocks that we can use day and night.
Some of our clocks will run for years without so much as a change of batteries or a
twist of a little knob. We have certainly developed the concept of time and
incorporated it into every moment of our lives.
Throughout history, time has been
determined by using the reflection of the sun, the phases of the
moon, and other calendars such as Stonehenge. Stonehenge, built over
4000 years ago in England, where used to tell ancient civilizations
the time of the day and year. Ancient peoples used lunar eclipses,
sun rays, the position of the sun, and other seasonal or celestial
events to determine the time. People used these stones to tell the
time of the day.
In 46 BC Julius Caesar decided
that the calendar year should have 365 days, but every fourth year
there should be an extra day, which would be a leap year. He adapted
this basis because if the year was divisible by four then it was to
be a leap year.
In 1582 Clauvius proposed the
Gregorian Calendar to Pope Gregory with an average year of 365.2425
days and 97 leap years every 400 years. The year was not to be a leap
year unless it were divisible by 100 and 400.
Today time can be easily
determined by reading a clock, watch, or even easier by a digital
clock.
Time Measurements
The common units for measuring time in the customary system are seconds, minutes, hours, days, weeks, month, and years.
The common units for measuring time in the customary system are seconds, minutes, hours, days, weeks, month, and years.
From the smallest unit of time
to the largest, they appear:
Reading a 24-Hour Clock
 |
 |
Many foreign countries and all
branches of the military services use a 24-hour clock to determine
their time. Some employees may also use a 24-hour clock to record
your work hours.
The 24-hour clock does not use
A.M. or P.M., instead all hours are counted on a 24-hour basis from
midnight to midnight. Times are shown as 4 digit numbers without
using a colon. Zeros are added if necessary to make a 4 digit number.
Hours from 1 P.M. to 11:59 P.M.
are found by adding the hour to 12.
Conversion Chart
|
- To change to a larger unit, divide.
- To change to a smaller unit, multiply.
Drill and Practice
Click on the pencil to choose your correct answer.1. The amount of time it takes to take a shower
 |
15 minutes |
|
15 hours |
2. The time it takes to wash one load of clothes
|
45 minutes |
|
45 seconds |
3. The time it takes to cook a turkey
|
6 minutes |
|
6 hours |
4. The time it takes to build a house
|
18 months |
|
18 years |
5. The time it takes to change the oil in a car
|
20 minutes |
|
20 days |
Answer the next questions on a sheet of paper and turn them in when you have completed them.
Write the equivalents.
6) 13 months = _______year _____months
7) 46 hours = ______minutes
8) 34 minutes = _______seconds
9) 68 weeks = _____years_____weeks
10) 987 day =______years ____months_____weeks___days
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