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A short class with Sarah and her students. The other ways are under More.
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Today, we are going to discuss fluid mechanics, particularly focusing on Newtonian and non-Newtonian fluids. Can anyone define what a fluid is?
I think a fluid is anything that can flow, like liquids and gases.
Exactly! Fluids are substances that can change shape easily without a fixed structure. Now, what do you think makes Newtonian fluids special?
Is it because they have a constant viscosity?
Correct! Newtonian fluids maintain constant viscosity regardless of the shear rate. A key point to remember is that shear stress is proportional to the shear strain rate. We can think of it as the equation σ = μ * (du/dy). Does anyone remember what each symbol represents?
σ is shear stress, μ is viscosity, and (du/dy) is the velocity gradient!
Great job! Let's summarize: Newtonian fluids are characterized by a linear relationship between shear stress and shear strain rate.
Moving on, let's discuss non-Newtonian fluids. What do you think happens to their viscosity when they’re subjected to stress?
I believe it changes, right? It's not constant!
Correct! Non-Newtonian fluids exhibit changes in viscosity depending on the shear rate. Can anyone give examples of non-Newtonian fluids?
Toothpaste seems to be one. It doesn't come out unless you apply a certain amount of force.
Exactly! Toothpaste is a Bingham plastic, which requires a yield stress to start flowing. It only deforms when that stress is exceeded.
What about the shear-thinning fluids like ketchup?
Great example! Shear-thinning fluids decrease in viscosity with increased shear rate. This 'thinning' behavior is common in many everyday substances.
So, is there a relationship we can see on a graph?
Yes! The graph will show the slope representing the apparent viscosity. We will visualize this in upcoming exercises.
Next, let’s discuss how temperature impacts the viscosity of fluids. Who can tell me how temperature affects liquids?
I think increasing the temperature decreases the viscosity of liquids.
That's right! As the temperature rises, molecular motion increases, leading to weaker intermolecular forces and thus lower viscosity. How do you think pressure impacts viscosity?
I believe increasing pressure has a minimal effect on liquids but can slightly affect gases.
Exactly! For liquids, pressure changes have little effect on viscosity, but for gases, increased pressure can enhance molecular interactions, slightly affecting the viscosity.
So, as temperature increases, gas viscosity rises?
Correct! Gases generally show increased viscosity with rising temperature. Remember, in contrast to liquids, the molecular motion dominates here.
These fluids exhibit constant viscosity regardless of shear rate.
These fluids demonstrate variable viscosity depending on the shear rate.
A measure of a fluid's resistance to flow, essential in discussing fluid behavior.
The relationship between these two concepts defines how fluids respond to external forces.
In a fluid, there it flows, Newton's rules are how it goes.
Imagine a river (Newtonian) that flows steadily without changing its shape, while a smoothie (non-Newtonian) thickens when blended harder.
Think of 'N.E. Viscous' - Newtonian Equals Viscosity Constant; Non-Newtonian Varies!
Remember 'V.S.N.' for 'Viscosity Shows Nature' to describe fluid behaviors.
Term
What is a Newtonian fluid?
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What is viscosity?
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What characterizes non-Newtonian fluids?
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Define Bingham plastic.
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A fluid whose viscosity remains constant regardless of the shear rate applied.
A fluid whose viscosity changes with different shear rates.
A measure of a fluid's resistance to flow.
The force per unit area exerted by a fluid parallel to a surface.
The rate of change in velocity across a fluid layer.
The rate of deformation of a fluid element due to shear stress.
A type of non-Newtonian fluid that requires a finite yield stress to start flowing.
A property of non-Newtonian fluids where viscosity decreases with increasing shear rate.
A property of non-Newtonian fluids where viscosity increases with increasing shear rate.
This section discusses the characteristics and behaviors of Newtonian and non-Newtonian fluids, focusing on viscosity and the impact of temperature on fluid properties.
In this section, we explore the principles of fluid mechanics as they relate to Newtonian and non-Newtonian fluids. Newtonian fluids maintain a constant viscosity regardless of shear rate, while non-Newtonian fluids exhibit varying viscosity under different conditions. The effects of temperature and pressure on the viscosity of fluids are also examined.
In this section, we delve into the concepts of Newtonian and non-Newtonian fluids, focusing primarily on how shear stress relates to shear strain rate. Newtonian fluids have a consistent viscosity that does not change with the rate of shear, while non-Newtonian fluids display variable viscosity that depends on how quickly they are deformed. The relationship between shear stress and shear strain is linear for Newtonian fluids, represented by the equation σ = μ * (du/dy), where σ is shear stress, μ is viscosity, and (du/dy) is the velocity gradient.
The section further discusses how temperature and pressure affect the viscosity of fluids, revealing that increasing temperature decreases viscosity in liquids due to weakened intermolecular forces, while for gases, viscosity typically increases with temperature due to enhanced molecular motion. We also explore special cases of fluids like Bingham plastics and shear-thinning/ shear-thickening fluids, emphasizing their unique behaviors under different conditions.