1. Galileo on
Motion
“My purpose is to set forth a very new
science dealing with a very ancient
subject. There is, in nature, perhaps
nothing older than motion, concerning
which the books written by philosophers
are neither few nor small; nevertheless I
have discovered by EXPERIMENT
some properties of it which are worth
knowing and which have not hitherto
been either observed or demonstrated.”
~ Galileo
3. Bridging the Gap:
Aristotle to Galileo
Philoponus
533 A.D.
Avicenna
980 A.D.
Oresme
1330’s
Buridan
Ockham
1300’s
4. Born in 1564 in Pisa of Vincenzo Galilei and Guilia Ammannati
Florence
University of Pisa; 1581-1585
Chair of Mathematics Univ. of Pisa 1589
Father dies in 1591; Professory of Mathematics at the University of
Padua
Meets Maria Gamba; Virginia (later Sister Maria Celeste) is born
(1600), Livia (1601), later Sister Arcangela, and Vincenzio (1606)
1609; the spyglass
Cardinal Robert Bellarmine
1616 wrote the Letter to the Grand Duchess
1630 wrote Dialogue Concerning the Two Chief Systems of the World
Inquisition bans the Dialogue and Galileo is sentenced to lifetime
house arrest
1634 his daughter, Virginia, dies
Disourses are smuggled out
Died 1642
Galileo’s Life
5. “Philosophy is written in this grand book, the universe, which
stands continually open to our gaze. But the book cannot be
understood unless one first learns to comprehend the
language and read the characters in which it is written. It is
written in the language of mathematics, and its characters
are triangles, circles, and other geometric figures without
which it is humanly impossible to understand a single word
of it; without these one is wandering in a dark labyrinth.”
Galileo – from The Assayer
6. Works
De Motu (1602-1604) never published
Dialogue Concerning the Two Chief
Systems of the World (1625-1630) -
1632
Discourses and mathematical
demonstrations concerning the two new
sciences (1633-1642)-1638
7. Galileo’s Qualifiers
Rectilinear vs. Circular Motion
Straight line motion or motion parallel with
the surface of the earth?
Criterion of Simplicity
Agreement with experiment
9. Naturally Accelerated
Motion/Constant Acceleration
Vs. uniform motion – motion in which
equal distances are covered in equal
increments of time
“A motion is said to be uniformly
accelerated when, starting from rest, its
speed receives equal increments in
equal times”
11. What do we make of this?
Finds that the distance of descent
always varies closely to the square of
the time
Algebra had yet to be applied to such
problems
The final velocity of the ball depended
on how high the plane was, not directly
to the plane’s incline angle
12. Projectile Motion
1. Constant downward acceleration
2. Maintains constant horizontal velocity
• Treat vertical and horizontal motions
independently
• Combination of two components will agree
with observed trajectory
•Observed trajectory is parabolic
13. Projectile Motion
Derived Equations
Horizontal x = vot
Vertical y = 1/2gt2
Parabolic y = ( g ) x2
Trajectory 2v2
o
15. The Components of Motion
http://www.makingthemodernworld.org.uk/larning_modules/maths/04.TU.02/?secti
on=7
16. Inertia
Momentum – product of the weight of a
body times its velocity
Inertia - a body in motion tends to stay
in motion (doesn’t specify straight-line)
http://id.mind.net/~zona/mstm/physics/mechanics/forces/g
alileo/galileoInertia.html
http://brunelleschi.imss.fi.it/genscheda.asp?appl=SIM&xsl=multimed&lingua=ENG&chiave=500135
17. Break from Aristotelian
Philosophy?
Objects are no longer “purposeful” – break
from teleology
***Disclaimer: Concepts of inertia did not begin
only with Galileo
