The Law Behind Weight and Tides: teacher key

Gravity, grade 7 edition, written for 7th grade. Newton's law of gravity explains weight, falling, tides and black holes. See what it says and where Einstein took the idea next.

Read the book. Print this page for the key.

Questions and answers

1. If you double the distance between two masses, what happens to the attraction between them?
   • It doubles
   • It falls to one-fourth (answer)
   • It stays the same
2. What changes from place to place?
   • Mass
   • The number of atoms
   • Weight (answer)
3. What did David Scott's hammer and feather show on the Moon?
   • The feather fell at the same rate as the hammer (answer)
   • The hammer floated
   • The feather fell faster
4. How does the Sun's tide-generating force compare with the Moon's?
   • About half (answer)
   • Twice as big
   • About the same
5. Do black holes suck in other matter?
   • Yes, from anywhere
   • No; from far away their gravity acts like any other object of the same mass (answer)
   • Only light

Words

• mass: amount of matter
• newtons: units of force
• tides: sea rising, falling
• horizon: black hole edge