Motion and Its Causes


How could you define your position on Earth?

GPS, or the Global Positioning System, was developed by the Department of Defense and was made operational in 1993. It consists of three parts. The first part is 24 satellites in 12-hour orbits that broadcast their location and the time the signal was sent. The second part is the control system that keeps the satellites in their correct orbits, sends correction signals for their clocks as well as updates to their navigation systems. The third component is the receiver. Some receivers are designed to be mounted in autos or trucks and display a map of the region around the receiver. Some are used by boaters to monitor their locations either in rivers or lakes or the open sea. Some are hand-held and can be used in the field by hikers and campers. Others are so small that they can be built into cell phones.

If you use a GPS device, you might find that your location is given as a latitude and longitude. For example it might give you latitude: 40° 26’ 28.43”N and longitude 80° 00’ 34.49”W. Note that these are angles, not distances. The reference for latitude is Earth’s equator. The reference for longitude is the “Prime Meridian” that runs through Greenwich, England (a suburb of London).


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