Across
- 2. when a gas turns into a liquid
- 4. to describe how something works or why something happens
- 7. water that falls back to Earth's surface
- 11. all organisms on Earth
- 13. when a liquid turns into a gas
- 18. a group of parts that work together
- 19. water in the form of an invisible gas
Down
- 1. all the land on Earth
- 3. matter that is made of more than one substance
- 5. to pull on an object, even without touching it
- 6. a group of atoms joined in a particular way
- 8. when water falls back to Earth and refills bodies of water (rivers, lakes, oceans)
- 9. the stuff that things are made of
- 10. all the water on Earth
- 12. a person who uses science knowledge to design something in order to solve a problem
- 14. a tiny piece of matter that is too small to see
- 15. all the air on Earth
- 16. water that has been used and now contains harmful substances
- 17. a supply of something that is useful
- 18. able to dissolve in water or another liquid