When Time Runs Slow: teacher key

Albert Einstein, grade 9 edition, written for 9th grade. The idea behind special relativity, how slower time shows up in muons, how mass becomes energy in stars, and the new theory of gravity that followed.

Read the book. Print this page for the key.

Questions and answers

1. What is impossible for any matter to do?
   • Travel faster than the speed of light (answer)
   • Make a clock
   • Reach the Earth
2. Why do muons made by cosmic rays reach Earth's surface?
   • Their time runs about 40 times slower than an observer on Earth experiences (answer)
   • They travel faster than light
   • They are made at the surface
3. What happens to the leftover mass in nuclear fusion?
   • It becomes a clock
   • It disappears into a compass
   • It becomes energy (answer)
4. What does the word fusion mean in this book?
   • Two nuclei merging into a heavier nucleus (answer)
   • A telescope
   • A kind of patent
5. How does E=mc2 explain the helium nucleus having less mass than its building blocks?
   • Helium has no mass
   • As binding energy (answer)
   • Helium is faster than light

Words

• fusion: nuclei merging