Page 101 - Understanding NCERT Science 09

or collision with the panels in front. Safety belts
Galileo Galilei was born
are worn to prevent such accidents. Safety belts
on 15 February 1564 in
exert a force on our body to make the forward
Pisa, Italy. Galileo, right
from his childhood, had motion slower. An opposite experience is
interest in mathematics encountered when we are standing in a bus
and natural philosophy. and the bus begins to move suddenly. Now
But his father we tend to fall backwards. This is because the
Vincenzo Galilei wanted sudden start of the bus brings motion to the
him to become a medical bus as well as to our feet in contact with the
doctor. Accordingly, floor of the bus. But the rest of our body
Galileo Galilei
Galileo enrolled himself opposes this motion because of its inertia.
(1564 – 1642)
for a medical degree at the When a motorcar makes a sharp turn at a
University of Pisa in 1581 which he never
high speed, we tend to get thrown to one side.
completed because of his real interest in This can again be explained on the basis of
mathematics. In 1586, he wrote his first the law of inertia. We tend to continue in our
scientific book ‘The Little Balance [La straight-line motion. When an unbalanced
Balancitta]’, in which he described
Archimedes’ method of finding the relative force is applied by the engine to change the
densities (or specific gravities) of substances direction of motion of the motorcar, we slip to
using a balance. In 1589, in his series of one side of the seat due to the inertia of
essays – De Motu, he presented his theories our body.
about falling objects using an inclined plane The fact that a body will remain at rest
to slow down the rate of descent. unless acted upon by an unbalanced force
In 1592, he was appointed professor of can be illustrated through the
mathematics at the University of Padua in following activities:
the Republic of Venice. Here he continued his
observations on the theory of motion and Activity ______________ 8.1
through his study of inclined planes and the
pendulum, formulated the correct law for • Make a pile of similar carom coins on
uniformly accelerated objects that the a table, as shown in Fig. 8.6.
distance the object moves is proportional to • Attempt a sharp horizontal hit at the
the square of the time taken. bottom of the pile using another carom
coin or the striker. If the hit is strong
Galileo was also a remarkable craftsman.
enough, the bottom coin moves out
He developed a series of telescopes whose
optical performance was much better than quickly. Once the lowest coin is
removed, the inertia of the other coins
that of other telescopes available during those
makes them ‘fall’ vertically on the
days. Around 1640, he designed the first
table.
pendulum clock. In his book ‘Starry
Messenger’ on his astronomical discoveries,
Galileo claimed to have seen mountains on
the moon, the milky way made up of tiny
stars, and four small bodies orbiting Jupiter.
In his books ‘Discourse on Floating Bodies’
and ‘Letters on the Sunspots’, he disclosed
his observations of sunspots.
Using his own telescopes and through his
observations on Saturn and Venus, Galileo
argued that all the planets must orbit the Sun
Fig. 8.6: Only the carom coin at the bottom of a
and not the earth, contrary to what was pile is removed when a fast moving carom
believed at that time.
coin (or striker) hits it.

90 SCIENCE

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