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February 2022
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A
clock
is a
device
that tells the
time
. Some clocks can only show the time. Other clocks can show other things. For example, some clocks can show the
date
as well as the time, or show other information, like the
timer
temperature
or the
weather
, some have stopwatch and some have alarm.
Clocks use different ways to measure time. Clocks need some sort of steady beat or
motion
to track the change in time. Ancient
water clocks
worked by the steady movement of
water
from a
container
with a hole in the bottom to another container without a hole. Other clocks use
pendulums
, springs and gears to track the change in time correctly.
Digital clocks work by measuring the
vibrations
of
quartz
crystals
when
charged
with
electricity
. The vibration
frequency
of the crystal does not change.
Atomic clocks
use the
electromagnetic waves
absorbed and emitted by atoms such as
caesium
to measure time. They are the most precise clocks in the world.watch image
The two most common types of
displays
on clocks are "
analog
" and "
digital
".
Analog clocks use
angles
to tell time. They have
hands
that
rotate
around the clock's
face
(the front of the clock). The position of the hands shows the time. The face of the clock is a flat
disk
. It will often have the numbers one through twelve on the face to make it easier to read. Analog clocks commonly have two or three hands. If it has two, there is a large hand or
minute
hand
and a smaller hand, the
hour
hand
. Clocks with three hands also have a
second
hand
. This hand is usually about as long as the minute hand, but much thinner.
Each hand shows the time it is named for and moves around the face of the clock one complete rotation for each movement to the next larger hand. For example, the second hand moves around the face of the clock in 60 seconds. It moves once each second. When it moves all the way around the clock, the minute hand moves forward one space. When the minute hand moves all the way around the face of the clock (which takes 60 minutes), the hour hand moves forward one section. The second and minute hands take 60 movements to move all around the face of the clock. The hour hand only needs 12 movements to do the same.
Digital clocks use
numbers
to show the time.
LCDs
and
LEDs
are common for digital clocks. Unlike analog clocks which are based on 12 hours, digital clocks can use either a
12-hour clock
(often with
am
for morning and
pm
for afternoon/night) or a
24-hour clock
. Digital clocks are usually smaller and easier to both use and read than analog clocks but they can also be made much larger. New digital clocks can even correct themselves using the
internet
or
radio
signals
.
There are also clocks that use sound, usually along with a dial or some other means, to show the time. The sound could be as simple as a
bell
or so complex that it sounds the same as a person. Many clocks that do this are old and are driven by
springs
or
weights
rather than
batteries
or other forms of
electric power
. Some special clocks are often used by people who are
blind
or cannot see well enough to read an analog or digital clock. They can also be used by people with
mental
problems that cause them to be unable to read other clocks.
There are many different types of clocks and watches. They are different in what they are used for, what they can do or how they are made. Examples include:
- A
wristwatch
, also called a watch, is worn on the wrist. It is held in place by two straps connected to the watch, and then wrapped around the wrist and connected to each other.
- A
pocket watch
is kept in a pocket. It usually has a small
chainor
a chain like cloth which is connected to the person's
clothing
. This helps people to not lose the watch.
- A radio (controlled) clock is automatically synchronized to a time, transmitted by a radio transmitter.
JUNGHANS MEGA
is the name of the world's first
radio
-controlled
wristwatch
with hands.
- A
sundial
is an old form of a clock which uses the
Sun
to tell time.
- An
alarm clock
is a clock that makes a
sound
(often a
buzzing
or a
bell
-like sound) or plays
music
at a certain time. It is used by people to wake up from
sleep
at a time they choose.
- A
grandfather clock
is a tall clock that stands on a floor. It uses a
pendulum
to tell time.
- A
cuckoo clock
is a pendulum based clock which makes a sound each hour on the hour. They often also have a small door. When the clock makes the sound, the door opens and a small
toy
bird
or other item usually comes out of the door.
- An
hourglass
, also called a sandglass or sand timer, uses
sand
trickling slowly to measure time.