An Etymological Dictionary of Astronomy and Astrophysics

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فرهنگ ریشه‌شناختی اخترشناسی-اخترفیزیک

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free-fall time
  زمان ِ افت ِ آزاد  
zamân-e oft-e âzâd
Fr.: temps de chute libre  

The characteristic time it would take a body to collapse under its own → gravitational attraction, if no other forces existed to oppose the collapse. It is given by: tff = (3π/32 ρ0 G)1/2,
where ρ0 denotes the initial density and G the → gravitational constant. Free-fall time is independent of the starting radius. Also known as → dynamical time scale.

See also: → free fall; → time.