 | In the Solar System, the Milky Way Galaxy, and throughout the universe, most objects don’t travel in straight lines; they move in circular or elliptical orbits around a more massive object.
Circular motion describes not only how satellites orbit the Earth but how wheels roll and what forces you feel when riding on a rotating amusement park ride.
When an object moves in a circle, its velocity constantly changes direction.
In order to change an object’s velocity, something else has to apply a force.
That centripetal force always points toward the center of the circle, which is why the force due to the Sun’s gravity keeps the planets moving in near circles around it.
|  | | By the end of this chapter you should be able to
|  | draw vectors of velocity, acceleration, and force for circular motion;
| | calculate angular velocity and centripetal acceleration and force;
| | draw free-body diagrams for circular motion problems;
| | describe the historical development of the concept of the gravitational force;
| | calculate gravitational force and describe how it depends on mass and distance; and
| | describe properties of planetary orbits and summarize Kepler’s laws.
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|  | 7A: Circular motion
7B: Orbits
7C: Extrasolar planets
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