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Fluid Mechanics Pressure Intensity Diagrams

  1. May 6, 2009 #1
    I was wondering if anyone could please explain what an intensity diagram would look like if you had a layer of fresh water ontop of x amount of meters of salt water (or vice versa). What is the concept behind this? How could you draw it? The question keeps popping up in past exam questions but i cant seem to find a way to awnser it since i have never been taught intensity diagram with two different substance densitys. Is it complicated or am i making it complicated? Thank you very much!
  2. jcsd
  3. May 7, 2009 #2
    Do you mean fluid at rest in different strata?? If so, heavier fluid(per unit volume or higher density) will be at the bottom.

    Do you know how pressure varies in fluid at rest? Just write a general equation for pressure at a point.

    Hint: pressure at a point at depth h = ρgh. Pressure at a point below depth h = ρgh + pressure due to second column below depth h
  4. May 7, 2009 #3
    Ok so does that mean if i draw the pressure intensity diagram of salt and freshwater, salt water is always going to be at the bottom because of its higher density and they are put on the same pressure intensity diagaram but i just label their different forces at their respective places? Do they have the same or independent gravity center? Thank you so much, i just really need to understand thiis concept. Please bear with me
  5. May 8, 2009 #4
    Correct. Think of why an air balloon rises up in water.

    Pressure varies linearly with depth of fluid. Lets say there are two liquids of densities ρ1 & ρ212) with column height h1 & h2 respectively. Pressure at point below these two columns = ρ1gh1 + ρ2gh2.

    Can you show what your attempt has been? It will be easier to help you that way.
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