Across
- 2. a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body
- 3. a large bag filled with gas so that it rises in the air
- 7. the force that causes something to fall to the ground
- 8. physical power which moves something
- 9. a gas which is lighter than air
Down
- 1. the sudden increased pressure against a vehicle when it travels at near the speed of sound
- 4. we need this gas to breathe
- 5. a machine which produces power to make a vehicle move
- 6. a large piece of material that fills with air and helps the wearer fall slowly to the