4.19. Orbital Motion http://www.ck12.org
Summary
- Orbital motion occurs whenever an object is moving forward and at the same time is pulled by gravity toward
another object. - The forward velocity of the object combines with acceleration due to gravity toward the other object. The
result is a circular or oval path called an orbit, in which one object keeps moving around the other. - Because of the relatively great gravity of the sun, Earth orbits the sun. The moon orbits Earth rather than the
sun because it is much closer to Earth.
Vocabulary
- orbit: Path of one object around another, such as the path of the moon around Earth or of Earth around the
sun. - orbital motion
Explore More
At the following URL, experiment with the gravity-and-orbit simulator. Set different initial velocities for the cannon
ball and observe whether the cannon ball crashes, escapes from Earth, or is set into orbit. Then answer the questions
below.
http://home.snc.edu/takamasatakahashi/login/AstroSp10/Animations/Active_Figures/10/
- Which range of initial velocities for the cannon ball puts it into orbit?
- What happens to the cannon ball if its initial velocity is less than this range?
- What happens to the cannon ball if its initial velocity is greater than this range?
Review
- Define orbit and orbital motion, and explain why orbital motion occurs.
- In addition to the moon, artificial satellites also orbit Earth. What factors do you think must be taken into
account to ensure that a satellite keeps orbiting Earth rather than falling back to Earth’s surface? - Earth is closer to nearby planets including Venus and Mars than it is to the sun. Why don’t these other planets
pull Earth toward them and cause it to veer off its orbit around the sun.