Galileo Galilei (1564 – 1642) Experiementalist Theoretician Annoyance to the Church “Modern” Scientist

Galileo’s Early Life Started as a Medical student Professor of Mathematics, Pisa, 1589 Moved to Padua, studied motion 1609 built a telescope

Why a Telescope? 1597 – Kepler wrote Galileo asking him to back Copernicus Built new telescope to check things out Calibrated telescope on earth Turned it towards the sky (uh oh)

Galileo’s major discoveries with the telescope  The moons of Jupiter  Planets are discs  Phases of Venus  Solar Rotation and Sunspots

“Minor” discoveries “Moons” of Saturn (actually the rings) Individual stars in the Milky Way Mountains and Craters on Moon’s surface

Galileo and the Church By 1611, won over most church officials Not Cardinal (Saint) Robert Bellarmine Bitterness ensues

Galileo’s solution Galileo ultimately says Scriptures are always right, BUT...  Must be interpreted in light of history and writing styles  Should use experiment to interpret scripture, not reverse  God gives us natural phenomena from which to learn, using our God given minds

Standoff with Church 1630 – Publishes “Dialogue Concerning the two Chief World Systems” Salvati represents Galileo (Copernicus); Simplicio represents an Aristotelean; Sagredo represents an intelligent, open minded layman

1631, Galileo gets Imprimatur for “Two Chief Worlds” when he adds an appendix by Simplicio that Coperican system is just a hypothesis 1633, Galileo is placed under house arrest, threatened with death, recants in June 1636 publishes “Discourses and Mathematical Demonstrations Concerning the two new sciences”

He who laughs last, laughs best!  “Two new sciences” was smuggled into Catholic countries  1822 Pope says Heliocentric Model is Okay  1985 Pope John Paul II says Galileo was wrongly convicted.

Gailieo and Motion: Kinematics Asking questions about... Where? When? How fast?

What is Natural Motion? Aristotle says things move in a straight line until stopped. Galileo thought about ramps: Going down: speeds up Going up: slows down Horizontal: stays the same??

Inertia By polishing ramps (troughs), Galilieo shows that an object in the absence of “roughness” (resistance) should continue moving forever. “An object in motion stays in motion; an object at rest stays at rest”

Falling objects Two choices for how objects fall:  Constant speed -> d  t  Constant acceleration -> d  t 2  But objects fall too fast to tell with the technology of the times

Galileo’s fixes Slow down motion -> Motion should be qualitatively the same going from 90° -> 89° -> 88° -> 85° -> 70° -> 30° and so on Improve timing: water clock Result: d  t 2 constant acceleration!

Kinematics Constant velocity v av = Δx/Δt v in = v on speedometer What if velocity (speed) changes?

Acceleration Acceleration a = Δv/Δt Gives v = v 0 + a t (v 0 is initial speed) and x = ½ a t 2 (starting from rest) This is all we will need for now

The equations of kinematics Constant speed x = v t Constant acceleration v = v 0 + a t starting from rest x = ½ a t 2