Page 166 - Science Class 07

An other important device used to measure 1 day = 24 hours
me in ancient me as an 'hour glass'. It was 1 hour = 60 minutes
also known as sand clock. It was based on the v They further divided one minute into 60
principle that a certain quan ty of sand falls
equal parts and called each part as a
from the upper chamber into the lower
second.
chamber in one hour.
1 day = 24 hours
1 hour = 60 minutes
1 minute = 60 seconds

Units of Time

60 second = 1 minute

60 minutes = 1 hour
24 hours = 1 day

Sand Clock 365 days = 1 year
10 year = 1 decade
TIME MEASUREMENT IN MODERN TIME
100 years = 1 century
Time measurement devices of the ancient
mes were based on rough es ma on. But, 1000 years = 1 millenium
with the development in the field of science
and technology, man required accurate me
MODERN TIME MEASUREMENT DEVICES
measurement devices.
v Pendulum was, perhaps, the first modern
The first big achievement in this regard was the me measurement device. It was invented
discovery of revolu on and rota on of the
by a Dutch scien st, Huggins in 1656. It was
earth. During the medieval period, people got based on the Galileo’s sugges on that the
to know the earth completes one revolu on in period of swing of a pendulum is constant.
a certain period of me. People called this me
A pendulum consists of a weight ed to a
dura on as a year. They also came to know that
string at the lower end. The upper end of
the earth rotates on its axis and completes one
rota on in a day. They counted the day that the string is a ached to a support. On
giving a li le push the pendulum makes to
falls in a year and found that the earth the
and fro movement from its posi on. The
completes one revolu on in about 365 days.
These facts helped the people in calcula ng length and weight of the pendulum is taken
in such a way that it takes one second for
accurate me.
one to and fro movement. The needle of
v Scien sts divided one day into 24 equal
the minute is set in such a way that it
parts and each part was called an hour.
moves one step further in 60 seconds and
1 day = 24 hours the needle of the hour moves one step
v They further divided an hour into 60 equal further when the needle of minute
parts and called each part as a minute. completes one full rota on.

166 Science-7