From Galileo's Slopes to the Principia: teacher key

Pushes and Pulls, grade 11 edition, written for 11th grade. Between 1564 and 1687, Galileo's experiments and Newton's Principia replaced the old idea that rest is natural. Newton's laws and the dispute over gravity across empty space followed.

Read the book. Print this page for the key.

Questions and answers

1. What did Aristotle teach about why earth and water move down?
   • They have lightness
   • They have heaviness by their nature (answer)
   • Gravity pulls on them
2. What happened when Galileo rolled a ball down one slope and up a facing slope?
   • It rose higher than it began
   • It stopped at the bottom
   • It rose to about the same height (answer)
3. By Galileo's law of free fall, how far does a ball drop if it falls twice as long?
   • Four times as far (answer)
   • Twice as far
   • The same distance
4. Why did Newton's Moon check matter?
   • It showed the Moon is 60 times heavier than Earth
   • One inverse-square force could explain both falling objects and the Moon's orbit (answer)
   • It proved gravity works only on Earth
5. Why did Newton's theory of gravity stay under dispute for much of the 18th century?
   • It had no mathematics
   • Nobody could read the Principia
   • It did not say how gravity pulls across empty space (answer)
6. In the passage about the Principia, what are propositions?
   • Derived statements in the book (answer)
   • Letters sent to Halley
   • Pages of the manuscript

Words

• manuscript: handwritten work
• Principia: Newton's book
• inertia: resisting change
• parabolic: curved path
• propositions: claims proved