super easy

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Across
  1. 2. a famous sentient's with three laws
  2. 4. a Greek work
  3. 6. a small peace of matter use for atom bombs
  4. 8. a branch of science dealing with mater and energy
Down
  1. 1. speeding up
  2. 3. slowing down
  3. 5. a type of ray that comes from the sun
  4. 7. how fast your going