1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Hydrostatics on plane surface (basic fluid mechanic Q)

  1. Apr 3, 2015 #1
    • HW Template missing as it was moved from another forum
    ?temp_hash=a20ac79e236529c76b2ff2b74bb4e03b.png

    I don't understand how they got the "position of individual forces".

    For F1, I'm guessing they used a pressure diagram and that's why it's 2/3 from the tip of the triangle. But why wouldn't the force act on the centroid for this square section (thus its 3.5/2)?
    ?temp_hash=a20ac79e236529c76b2ff2b74bb4e03b.png
    But for position of F2 (y2), they used the equation. Can you explain this?
     

    Attached Files:

  2. jcsd
  3. Apr 8, 2015 #2
    Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
     
  4. Apr 8, 2015 #3

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    The hydrostatic force F1 doesn't act at the centroid of the square because it's not constant with respect to depth. You must integrate the pressure distribution acting over the area to find the magnitude of the force F1, and then calculate the first moment of this force with respect to the waterline in order to locate the point at which the hydrostatic pressure acts.

    Since the pressure distribution is triangular w.r.t. depth, it's easy to calculate the total hydrostatic force and to find the center of pressure, knowing some geometric facts about triangles.
    ?temp_hash=a20ac79e236529c76b2ff2b74bb4e03b.png
    Since the top of the square is at the waterline for the body, the pressure distribution is pretty simple: it's a triangle. No complicated formulas are required to find the center of pressure.

    For the bottom of the body, the bottom is sloping and the pressure distribution is trapezoidal, so there are no easy formulas to apply except the one shown in the solution.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Hydrostatics on plane surface (basic fluid mechanic Q)
Loading...