is launched at a slow speed, it will fall back to Earth, as in paths A and B in the figure.
However, if it is launched at a fast enough speed, the Earth below will curve away at the
same rate that the cannonball falls, and the cannonball will go into a circular orbit, as in
path C. If the cannonball is launched even faster, it could go into an elliptical orbit (D) or
leave Earth’s gravity altogether (E).
Figure 23.20: Isaac Newton explained how a cannonball fired from a high point with enough
speed could orbit Earth. ( 25 )
Note that Newton’s idea would not actually work in real life; a cannonball launched from
Mt. Everest, the highest mountain on Earth, would burn up in the atmosphere if launched
at the speed required to put the cannonball into orbit. However, a rocket can launch straight
up, then steer into an orbit. A rocket can also carry a satellite above the atmosphere and
then release the satellite into orbit.
Types of Satellites
Since the launch of the first satellite over 50 years ago, thousands of artificial satellites
have been put into orbit around Earth. We have even put satellites into orbit around
the Moon, the Sun, Venus, Mars, Jupiter, and Saturn. Imaging satellites are designed for
taking pictures of Earth’s surface. The images can be used by the military, when taken by