Satellites in Orbit
Artificial satellites are launched into orbit by a rocket or space shuttle. Why doesn't a satellite in a high orbit need to fire rocket engines continuously to remain in orbit? Much like the moon, the satellite needs only the centripetal force provided by gravity and its inertia to maintain its orbit. Satellites in a low orbit, however, are slowed by friction with Earth's atmosphere. As a satellite loses speed, it loses altitude. Eventually, the satellite reenters Earth's atmosphere and burns up.
Uses of Satellites
Currently, there are thousands of artificial satellites orbiting Earth. These satellites perform many functions. They monitor Earth's weather, create detailed radar maps of Earth's surface, use telescopes to gaze deep into space, and study Earth's climate. Some satellites, like the one shown in Figure 23, receive and transmit radio and microwave signals. Numerous communication satellites are used to receive and transmit cell phone and satellite television signals.
The next time you watch an event on television transmitted by satellite from another part of the world, you should thank Isaac Newton. His work to discover the laws of motion and universal gravitation have led to the development of countless modern technologies.
Figure 23 Satellites are used to receive and transmit electromagnetic waves over great distances.
Section 12.4 Assessment
Reviewing Concepts
Which universal force can repel as well as attract?- Which universal force acts to hold the nucleus together?
- State in your own words what is meant by Newton's law of universal gravitation.
How does friction with the atmosphere affect the speed of an artificial satellite?
Critical Thinking
Using Models The moon in its orbit around Earth behaves like a ball at the end of a string being swung above your head. Explain the forces involved.
Predicting If the speed of an orbiting satellite decreases, how might you expect its orbit to change?
Inferring Explain how Newton's third law and his law of universal gravitation are connected.
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