科学素养与生活应用·英语30篇（1）

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为何手机GPS需要四颗卫星，而非一颗

GPS calculates position by measuring how long signals take to travel from satellites.
Because light speed is constant, timing errors translate directly into distance mistakes.
Three satellites give you latitude, longitude, and altitude—but only if your clock is perfect.
Your phone’s internal clock isn’t accurate enough, so a fourth satellite helps correct timing drift.
This process, called trilateration, works in three dimensions, not just on a flat map.
Engineers designed the system to handle atmospheric delays and signal reflections too.
Even tiny timing errors—just one microsecond—would misplace you by 300 meters.
So precision engineering, physics, and real-time computation all work together silently.