Light, Time and Special Relativity: teacher key

Albert Einstein, grade 8 edition, written for 8th grade. The puzzle about light, the two ideas of special relativity, slower time and E=mc2, and what came after for Newton's equations.

Read the book. Print this page for the key.

Questions and answers

1. What did Michelson and Morley find when they sent light beams along and across Earth's motion?
   • No difference (answer)
   • A big difference
   • That light stopped
2. According to relativity, what happens to a twin who travels near the speed of light and returns?
   • The twin is older
   • The twin is younger than the twin who stayed on Earth (answer)
   • The twin is the same age
3. What does E=mc2 say?
   • Mass equals time
   • Light equals gravity
   • Energy equals mass times the speed of light squared (answer)
4. What does general relativity say gravity is?
   • How mass warps space and time (answer)
   • A kind of light
   • A clock that runs slow
5. What is space-time?
   • A kind of clock
   • A telescope
   • A fabric that unites space and time (answer)