P2: F

P2: F

1. The planets orbit the Sun as gravity pulls the planets towards the Sun.

2. Manned spacecraft

   • Spacecrafte with people on board.
     • Extremely complex systems are installed.
     • The cost for missions, per mission are high.
     • Can fix wreckages.

3. Unmanned spacecraft

   • Spacecraft without people on board.
     • Do not need to supply water, oxygen or food.
     • Can go to places with extreme locations.
     • Systems can fail and missions can be lost.

4. Definitions

   • Light year: the distance light can travel in a year.
     • Measures the distance in space.
   • Star: a ball of burning gas.
   • Orbit: a circular path around an object caused by the gravitational pull.
   • Gravity: keeps the planets in orbit around the sun.
   • Planet: an object that orbits the sun.
   • Solar System: a star and its planets.
   • Galaxy: a collection of stars.

5. Uses of artificial satellites:

   • Collecting information for weather forecasts.
   • Communications:
     • Broadcasting t.v. programmes.
     • Relaying telephone calls.
   • Satellite navigation systems.
   • Spying

6. Gravity is the centripetal force that keeps planets moving around the Sun, and satellites moving around planets.

7. These objects continuously change direction as they move in a circle. This needs a resultant force to act on the object. This force is the centripetal force. The centripetal force pulls an object toward the centre of the circle.

   • Circular motion requires a centripetal force.

8. What are some of the difficulties of manned space travel between planets.

   • High levels of ionizing radiation.
   • Lack of: pressure, food and water and oxygen
   • Large temperature swings between sunlight and shade.

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