Shear stress is really important when we talk about Newtonian and Non-Newtonian fluids. It's exciting to learn about this if you're interested in fluid mechanics!

Newtonian Fluids:

• What are they? Newtonian fluids are liquids like water and air that have a constant thickness, known as viscosity.
• How do they behave? In these fluids, shear stress ($\tau$) changes directly with the shear rate ($\dot{\gamma}$). You can think of it like this: $\tau = \mu \dot{\gamma}$ Here, $\mu$ represents the viscosity.
• What does this mean? Because of this direct relationship, we can always predict how these fluids will flow, no matter how fast they’re moving.

Non-Newtonian Fluids:

• What are they? Non-Newtonian fluids are things like ketchup or some glue that don't have a constant viscosity.
• How do they behave? In these fluids, shear stress does not change directly with the shear rate, which leads to some interesting behaviors, like:
  • Shear-thinning (Pseudoplastic): This means these fluids get thinner when you stir them more (like when you mix paint).
  • Shear-thickening (Dilatant): These fluids get thicker when you stir them more (like cornstarch mixed with water).
  • Bingham Plastics: These fluids need a little push (called yield stress) to start flowing (like squeezing toothpaste).

Conclusion:

By understanding how shear stress works with these two types of fluids, we can see how liquids behave differently in many engineering situations. Fluid mechanics is really cool! Let’s learn more about these interesting properties!