Lesson 10: Galileo’s Astronomy and Newton’s Gravitation

10. Lesson 10: Galileo’s Astronomy and Newton’s Gravitation#

Galileo’s Big Mouth and Newton Explains the Solar System

The Lion Roars. In 1697, a calculus-based mathematical competition was held throughout Europe. Newton was long out of physics, but entered what became the winning entry anonymously. Noted the sponsor of the challenge, “we recognize the lion by his claw.”

“They know that as to the arrangement of the parts of the universe, I hold the Sun to be situated motionless in the center of the revolution of the celestial orbs while the Earth rotates on its axis and revolves about the Sun. They know also that I support this position not only by refuting the arguments of Ptolemy and Aristotle, but by producing many counter-arguments; in particular, some which relate to physical effects whose causes can perhaps be assigned in no other way.” Galileo, Letter to Grand Dutchess Christina, 1615.

Everyone knows the highlights of the Galileo story and his embarrassment at the hands of Pope Urban VII. The real story is perhaps different from the urban legends. (See what I did there?) As in his experiments on terrestrial motion, his conclusions on the Moon’s and planets’ motions were more descriptive than causal. They “why” – the dynamics – of the cosmos was left to Isaac Newton to figure out. His Gravitational Model was so successful, that in the space of his lifetime, Europe went from ignorant of how Nature worked, to believing that everything can be known. The so-called “Age of Reason” itself owes much of its independence-inclined mindset to Newton’s work.

  Goals of this lesson:

Understanding, Appreciation, and Familiarity

I’d like you to Understand:

  • How to calculate the gravitational force between two masses

  • How to calculate the weight of any object on any planet

  • How to calculate gravitational potential energy

I’d like you to Appreciate:

  • How Galileo’s astronomical discoveries charted new ground in astronomy

  • How Galileo’s approach to science laid groundwork for the modern version

  • Newton’s argument regarding the Moon and the Apple

  • What being in orbit implies about “falling”

  • Escape velocity

  • That gravitational potential energy is negative

I’d like you to become Familiar With:

  • The later lives of Galileo and Newton

  • The importance of Galileo’s Letter to the Dutchess Catherine