Fluid Mechanics Pressure Intensity Diagrams

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Discussion Overview

The discussion centers around the concept of pressure intensity diagrams in fluid mechanics, specifically when dealing with layers of fluids of different densities, such as fresh water and salt water. Participants explore how to represent these layers in a diagram and the underlying principles of pressure variation in fluids at rest.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification, Homework-related

Main Points Raised

  • One participant seeks clarification on how to create an intensity diagram for a system with fresh water and salt water, expressing confusion about the concept and its representation.
  • Another participant suggests that in a fluid at rest, the denser fluid will be at the bottom, indicating that pressure varies with depth according to the equation P = ρgh.
  • A subsequent reply confirms that salt water, being denser, will always be at the bottom in the diagram and questions whether the gravity centers of the two fluids are the same or independent.
  • Further clarification is provided that pressure varies linearly with depth and gives a general equation for pressure at a point below two fluid columns of different densities.
  • Participants encourage sharing attempts at drawing the diagram to facilitate better assistance.

Areas of Agreement / Disagreement

Participants generally agree on the principle that denser fluids will be positioned lower in the diagram, but there is uncertainty regarding the representation of gravity centers and how to effectively draw the intensity diagram.

Contextual Notes

Some assumptions about fluid behavior and pressure calculations may not be fully articulated, and the discussion does not resolve how to depict the interaction between the two fluids in the diagram.

feot09
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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 can't 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!
 
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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
 
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
 
feot09 said:
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
Correct. Think of why an air balloon rises up in water.

Pressure varies linearly with depth of fluid. Let's 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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