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How can i calculate the speed of an object in water

  1. Sep 15, 2010 #1
    I would like to know how fast an object will move through sea water.
    Do you know if an accurate figure can be calculated? if so how?
    I would like to know how fast 100 tonnes of steel -(streamlined )would fall through sea water.
    I would also like to how how to calculate the figure for any object.
  2. jcsd
  3. Sep 15, 2010 #2
    For a rough approximation you can just calculate gravity vs. buoyancy forces to determine the acceleration.

    For a more accurate calculation you will need to take into account drag forces.
  4. Sep 15, 2010 #3


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  5. Sep 16, 2010 #4
    thanks for your replies,

    Vt = terminal velocity,
    m = mass of the falling object,
    g = acceleration due to gravity,
    Cd = drag coefficient,
    ρ = density of the fluid through which the object is falling, and
    A = projected area of the object.

    i just want to chack i understnad the equation...

    ( 2xmass x accelaration gravity) divided by (density x area x drag coefficient)
    = X square root of x = Vt

    how accurate is this euquation considered to be; what is still missing.?

    I put some very dense materials in with very low drag coefficients and i got figure up to 65 metre per second which seems a little fast

    i got other things in and think that the figure is more realistic by making the drag coefficient 1 rather than 0.09.
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