Galileo: Early Years
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Born 15 Feb. 1564 in Pisa
Educated in Camaldolese Monastery
Father wanted him to be a medical
doctor
Interested in mathematics
Discoveries
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Observed swinging lamps in Cathedral
of Pisa and found period to be
independent of the amplitude – idea for
a pendulum clock
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Used inclined planes to prove that
bodies do not fall with velocities
proportionate to their weight but
proportionate to time.
Found that projectiles
follow a parabolic path
Galileo and the Telescope
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Galileo is correctly credited with the first
use of the telescope for viewing objects
in the heavens, but letters between him
and friends suggest that he first had
other, more pragmatic applications for
the telescope. He believed that he could
make money selling his telescopes to
wealthy Italian princes so that they could
use them for military purposes
1609 Letter:
The power of my cannocchiale [telescope] to show distant
objects as clearly as if they were near should give us an
inestimable advantage in any military action on land or
sea. At sea, we shall be able to spot their flags two hours
before they can see us; and when we have established the
number and type of the enemy craft, we shall be able to
decide whether to pursue and engage him in battle, or take
flight. Similarly, on land it should be possible from elevated
positions to observe the enemy camps and their
fortifications.
1610 Letter:
"I have many and most admirable devices; but they could
only be put to work by princes because it is they who are
able to carry on wars, build and defend fortresses, and for
their regal sport make most splendid expenditures."
Galileo’s Telescope
• Improved Dutch spyglass to
achieve 8-9X magnification
• Observed mountains on the
moon, the Milky Way
composed of tiny stars, and
sunspots
Reconstruction of Galileo
Telescope – about 1.5 inches in
diameter, with very long focal
length (meaning rather small field
of view)
You will behold through the looker a host of other
stars, which escape the unassisted sight, so numerous
as to be beyond belief. Stars of the seventh magnitude
appear with the aid of the looker larger and brighter
than stars of the second magnitude seen with the
unassisted sight
COPERNICAN THEORY
• I hold that the Sun is located at the centre of the
revolutions of the heavenly orbs and does not change
place, and that the Earth rotates on itself and moves
around it. Moreover ... I confirm this view not only by
refuting Ptolemy's and Aristotle's arguments, but also
by producing many for the other side, especially some
pertaining to physical effects whose causes perhaps
cannot be determined in any other way, and other
astronomical discoveries; these discoveries clearly
confute the Ptolemaic system, and they agree
admirably with this other position and confirm it.
• In February 1632 Galileo published Dialogue
Concerning the Two Chief Systems of the World Ptolemaic and Copernican . ,
GALILEO ASTRONOMY BOOK
 In February 1632 Galileo published Dialogue Concerning the
Two Chief Systems of the World - Ptolemaic and Copernican .
 In 1633 he was suspected of heresy based on this book which
was then placed on the Forbidden book list
 It was removed from that list in 1835 (not that stellar parallax
still had not been detected)
 Note that his observations that confirmed the Copernican
theory to him were made in 1610
 Note also, that Kepler's’ first and second law are published in
1609 – did Kepler and Galileo communicate?
1638: DIALOGUES CONCERNING THE
TWO NEW SCIENCES
 Galileo's ideas about motion are presented in lively fashion as a
dialogue involving three characters, Salviati, Sagredo and
Simplicio. The official Church point of view, that is,
Aristotelianism, is put forward by the character called Simplicio,
and usually demolished by the others. Galileo's defense when
accused of heresy in a similar book was that he was just setting
out all points of view, but this is somewhat disingenuous --Simplicio is almost invariably portrayed as simpleminded .
 the Salviati character remarks:
I greatly doubt that Aristotle ever tested by experiment whether it be true
that two stones, one weighing ten times as much as the other, if allowed to
fall, at the same instant, from a height of, say, 100 cubits, would so differ
in speed that when the heavier had reached the ground, the other would
not have fallen more than 10 cubits.
GALILEO AND SCIENTIFIC METHOD
• 1602-Pendulum experiments.
• 1604- Inclined plane experiments of natural
acceleration.
• 1607-Systematic manipulation of shapes and
weights of wax balls to study flotation.
• Investigation of projectile motion. Discovery of
parabolic character of projectile motion.
• 1609 Observations of Jupiter Moons
Three Experiments
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1. The Pendulum: Used to demonstrate the law of
inertia and that heavy and light bodies fall at the same
rate. Galileo also discovered the mathematical laws
governing the length of the string, the period of the
motion, and the amplitude of the swing.
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2. The Inclined Plane and the Rate of Acceleration:
Galileo used the inclined plane to slow the motion of
falling objects enough to accurately measure how their
speed increased.
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3. Projectile Motion: Galileo also used the inclined
plane to control the speeds and heights of projectiles in
order to discover the mathematical properties of their
paths.
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"...repeat many times the fall through a small height in such away
that I might accumulate all those intervals of time that elapse
between the arrival of the heavy and light bodies respectively at
their common terminus, so that this sum makes an interval of time
which is not only observable, but easily observable."
"...two balls, one of lead and one of cork, the former more than a
hundred times heavier than the latter, and suspended them by
means of two equal fine threads, each four or five cubits
long. "This free vibration repeated a hundred times showed clearly
that the heavy body maintained so nearly the period of the light
body that neither in a hundred swings nor even in a thousand will
the former anticipate the latter by as much as a single moment, so
perfectly do they keep step."
Galileo
Inclined Plane
"...in such a plane, just as well as in a vertical plane, one
may discover how bodies of different weight behave..."
Galileo
Inclined Plane
Total distance traveled is proportional to the square of time.
Projectile Motion
Projectile Motion
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The object goes into free fall as it
exits the inclined plane
Vertical motion can be separated
from the horizontal motion