Chapter 2: Forces

Miss Luzma Fabre

Section 5: Rockets and satellites

• Sputnik I was the first Earth-orbiting artificial satellite (1957). It was launched by the Soviet Union

• Then, in 1958, USA launched a satellite called Explorer I.

How do rockets lift off?• Rockets and space shuttles

lift into space 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

• If the upward pushing force (thrust) is greater than the downward pull of gravity, the rocket will accelerate upward

The Saturn V (five) rocket was developed in 1960’s. How do these multistage rockets work?

• Once a stage uses up its fuel, the container drops off and the next stage ignites

What is a satellite?• Rockets are used to carry

satellites into space• A satell i te is any object that

orbits another object in space• Artificial satellites are

designed for different purposes:

• Communication• Military intelligence• Weather analysis• Geographical surveys

• Circular motion• Satellites travel around Earth in circular

paths• They are constantly changing direction=

accelerating, so a force must be acting on them

• CENTRIPETAL FORCE

• Any force that causes an object to move in a circular path is a centripetal force

• The gravitational force is the centripetal force that pulls the satelite toward the center of the Earth

• Does a satellite require fuel once it is in orbit? Why?

• No, because it continues to move ahead due to its inertia. At the same time, gravity continuously changes the satellite´s direction

• Satellites in orbit around Earth continuously fall toward Earth, but because Earth is curved they travel around it.

• Is like a falling projectile that keeps missing the ground

• The faster a projectile is thrown, the farther it travels before it hits the ground. A projectile with enough velocity (7900 m/s) moves in a circular orbit

Launch Speed less than 8000 m/s Projectile falls to Earth

Launch Speed equal to 8000 m/s Projectile orbits Earth - Circular Path

• Satell i te location• They orbit at different heights,

depending on their uses• Ex: communications satellites travel

about 36000 km above Earth´s surface