Testing Gravity: teacher key

Gravity, grade 9 edition, written for 9th grade. Gravity became a law, then an idea about curved space. Follow the tests that put each idea on trial, from the Moon's fall to starlight bent by gravity.

Read the book. Print this page for the key.

Questions and answers

1. Why did Edmond Halley pay to publish the Principia?
   • He was Newton's teacher
   • The Royal Society was short of funds (answer)
   • Einstein asked him
2. How far must the Moon fall toward Earth each second to stay in orbit?
   • About 1.4 millimeters (answer)
   • About 1.4 meters
   • About 14 kilometers
3. Which observation could Newton's gravity not explain?
   • Falling apples
   • The motion of Mercury's orbit around the Sun (answer)
   • Tides
4. What did the 1919 measurements arguably align with?
   • Einstein's general relativity (answer)
   • Galileo's law
   • Halley's comet
5. What did the GRACE spacecraft measure?
   • Variations in Earth's gravity (answer)
   • The Sun's heat
   • Ocean salt

Words

• Principia: Newton's book
• precession: orbit slowly turning
• lensing: light bending