Doomlearn
DE
Science & TechFact

Without Einstein, your sat-nav would drift 10 km per day.

GPS satellites carry atomic clocks and orbit at about 14,000 km/h, 20,000 km up. Their speed makes the clocks run roughly 7 microseconds per day slow; the weaker gravity up there makes them run about 45 microseconds fast. Net effect: 38 microseconds ahead per day. Uncorrected, position errors would grow by around 10 kilometres daily.

Useful: The clocks are deliberately set slightly slow before launch so they tick exactly right in orbit.

Source: en.wikipedia.org

PhysikRelativitaetTechnik

Difficulty:

Question on this card

How do GPS satellite clocks compare with clocks on the ground?

  1. Exactly the same
  2. Net about 38 microseconds per day fast
  3. Net about 38 microseconds per day slow
  4. One second per day fast
Show the answer

Correct: Net about 38 microseconds per day fast

The gravitational effect outweighs the velocity effect, so the clocks run fast overall.

Related cards

Keep reading

This card belongs to the topic Science & Tech. Every card is short, cites a source and can be saved – due ones come back by themselves later.

About Doomlearn · Projects · Legal notice · Privacy · Terms