Student text Pages ROCKETS AND SATELLITES

TOPIC: ROCKETS AND SATELLITES  How does a rocket lift off the ground?  The awesome achievement of lifting a huge rocket into space against the force of gravity can be explained using Newton’s third law of motion.  A rocket can rise into the air because the gases it expels with a downward action force exert an equal but opposite reaction force on the rocket.

 As long as this upward pushing force, called thrust, is greater than the downward pull of gravity, there is a net force in the upward direction.  As a result, the rocket accelerates upward.

What keeps a satellite in orbit?  A satellite is any object that travels around another object in space.  Artificial satellites are launched into orbit around Earth.  They aid in space research, communications, military intelligence, weather analysis, and geographical surveys.

 Artificial satellites travel around Earth in an almost circular path.  Any force that causes an object to move in a circular path is called a centripetal force.  The word centripetal means “center- seeking.”  For a satellite that orbits Earth, the centripetal force is the gravitational force that pulls the satellite toward the center of Earth.

 Satellites in orbit around Earth continually fall toward Earth, but because Earth is curved, they travel around it.  The faster an object is thrown, the farther it travels before hitting the ground. If thrown fast enough, an object will go around Earth.  Although a satellite in orbit falls because of gravity, Earth’s surface curves away from the satellite at the same rate.

 The speed with which an object must be thrown in order to orbit Earth is about 7,900 m/s.  Satellites are placed into orbits that are varying distances from the center of Earth.  Satellites in higher orbits travel more slowly and take longer to circle Earth than do satellites in lower orbits.

 For example, a satellite in low orbit might take less than 2 hours to circle Earth.  A satellite orbiting about 36,000 kilometers above the surface of Earth takes about 24 hours to circle Earth.  Since Earth rotates once every 24 hours, a satellite above the equator always stays above the same point on Earth as it orbits.

HOMEWORK Chapter 2 Section 5 Assessment Page 67 Student Text 1-2 all Parts Students who need to check out a textbook need to do so end of day.