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Calculation required

  1. Dec 16, 2008 #1
    hello everyone

    Iam wonderind if somone could help me?

    I need to find out how long it would take for a Stainless steel ball 1.0" Dia With a density of 8.0g/cm qubed through 2000m of sea water with a density of 1026kg/m qubed and what impact force it would genorate.

    again this calc would need to be done with a Bakelite ball with a densaty of 1.25g/cm qubed.

    If somone could point me in the right direction it would be grately appreciated.
  2. jcsd
  3. Dec 16, 2008 #2


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    The terminal velocity in a fluid is fairly simple (http://en.wikipedia.org/wiki/Terminal_velocity#Terminal_velocity_in_the_presence_of_buoyancy_force)
    Note: Cd for a sphere is about 0.47
    Assuming that the density of seawater doesn't change over 2000m and that the flow is smooth.

    Is you assume it reaches terminal velocity pretty quickly compared to the 2000m total then you can just assume that it takes time = 2000m/terminal_velocity.

    Impact force is a little more difficult - the FORCE doesn't depend on the speed it hits with but the rate at which it slows down as it hits. So it is totally dependant on the stiffness of the sea floor - this is why an object falling from the same height onto say concrete would break but would survive landing in mud.
  4. Dec 16, 2008 #3
    I assume the ball has accererated to it's teminal velocity. Be carefull what equation you use. Terminal velocity is different for objects falling in liquids comopared to gasses.
  5. Dec 17, 2008 #4
    The ball will be coming to rest on a steel section of tooling so pritty hard stuff.

    Thanks for the imput folks.
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