ROCKETS AND SATELLITES Student text Pages 64 67

ROCKETS AND SATELLITES Student text Pages 64 -67

TOPIC: ROCKETS AND SATELLITES Ø How does a rocket lift off the ground? ØThe awesome achievement of lifting a huge rocket into space against the force of gravity can be explained using Newton’s third law of motion. Ø 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.

ØAs 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. ØAs a result, the rocket accelerates upward.

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

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

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

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

ØFor example, a satellite in low orbit might take less than 2 hours to circle Earth. ØA satellite orbiting about 36, 000 kilometers above the surface of Earth takes about 24 hours to circle Earth. Ø 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.