GPS, the Global Positioning System, lets phones, cars, ships, airplanes, and map apps find locations on Earth. It matters because accurate position helps people navigate, make maps, track weather data, guide emergency responders, and study movement across the planet. GPS connects geography with geometry because it uses distances, spheres, coordinates, and precise time measurements.
A map pin on a screen is the result of signals traveling from satellites far above Earth.
Key Facts
- GPS stands for Global Positioning System.
- GPS satellites orbit about 20,200 km above Earth.
- Distance can be found from signal travel time: d = vt.
- Radio signals travel at about c = 3.00 x 10^8 m/s.
- A receiver needs signals from at least 4 satellites to find latitude, longitude, altitude, and clock error.
- Location is found by trilateration, using overlapping distance spheres from satellites.
Vocabulary
- GPS
- GPS is a satellite navigation system that uses radio signals to determine a receiver's position on Earth.
- Trilateration
- Trilateration is the process of finding a location by using distances from known points.
- Satellite
- A satellite is an object that orbits a planet and can send or receive signals.
- Coordinate
- A coordinate is a number or set of numbers that describes a position on a map or grid.
- Signal delay
- Signal delay is the time between when a signal is sent and when it is received.
Common Mistakes to Avoid
- Calling GPS triangulation instead of trilateration. GPS mainly uses distances from satellites, not angle measurements.
- Forgetting that a fourth satellite is needed. Three satellites can locate a point in ideal geometry, but the fourth corrects the receiver's clock error.
- Assuming GPS satellites take photos of your location. GPS receivers calculate position from timed radio signals, not from satellite images.
- Ignoring units when using d = vt. Time must be in seconds and speed in meters per second if the distance answer is in meters.
Practice Questions
- 1 A GPS signal travels at 3.00 x 10^8 m/s and reaches a receiver after 0.067 s. How far did the signal travel in meters and kilometers?
- 2 A satellite is 20,200 km above Earth's surface. If a radio signal travels at 300,000 km/s, about how long does the signal take to reach a receiver directly below the satellite?
- 3 Explain why a GPS receiver needs signals from several satellites instead of just one satellite to place a map pin accurately.