1. 1

2. Space Travel 2

3. Scientists use what they know about forces and motion 3 when they send rockets into space

4. Gravity pulls things toward Earth 4

5. In order to lift rockets into space, 5 powerful engines are needed

6. The force of the rocket engines must be greater 6 than the force of gravity which is 9.8 meters/second/second

7. 7 In that way the rockets can escape Earth’s powerful pull

8. Some rockets carry satellites 8 Vocabulary: satellites an object that orbits, or moves around, Earth

9. Once a satellite is in space, 9 the force from its engine balances the force from Earth’s gravity

10. Then the satellite circles Earth 10 the way the moon circles Earth

11. Some satellites are put into space to study the weather on Earth 11

12. Other satellites send radio and television signals around the world 12

13. Some rockets explore other planets a 13 and their natural satellites, or moons