Earth's Motions and Earth-Sun Relationships Study Guide, Physical Geography, College of Alameda College of Alameda Physical Geography UNIT 14. The study of the earth s motions is a starting point for understanding the workings of the global ecosystem . The earth's two main motions are rotation and revolution . Rotation is the earth turning on its imaginary axis like a top.
Revolution is the earth s orbit around the sun.
The earth rotates west to east on its axis once a solar day. Rotation produces a set of physical consequences such as the daily rhythm of light and heat , the coriolis effect , tides , and the oblate ellipsoidal shape of the earth. Rotation is a device for establishing reference points and lines on the globe such as the poles , equator , parallels of latitude and meridians of longitude. Places on the earth's surface are located using a network of lines called a geographic grid . Map projections use the geographic grid to show a round globe on a flat map.