4.7. Conclusion and Summary

Now let us commit that how does the temperature effect on the coefficient of the viscosity.

This section begins by addressing the effect of temperature on the coefficient of viscosity, which describes how a fluid's resistance to flow changes with temperature. As temperature increases, molecular motion increases, which typically leads to a decrease in viscosity for liquids.

Consider honey at room temperature – it flows slowly due to its high viscosity. However, if you heat the honey, it flows much more easily. This illustrates how increasing temperature reduces viscosity and makes a fluid flow more freely.

So change of the pressures if you try to understand it that what does not change that significantly the molecular motions...

In this part, the text discusses the effect of pressure on viscosity. Unlike temperature, increasing pressure has little effect on molecular motion in liquids, resulting in only minor changes in viscosity (less than 0.5% change at high pressures).

Think about a soda can. When you shake it (increasing pressure inside), you notice a fizz when you open it, but the viscosity of the soda doesn't change much with the pressure buildup. It's a good reminder that pressure impacts the state but not necessarily the instant fluid behavior.

If you look at in terms of molecular motion as a mass exchange and the momentum exchange...

Here, we consider how the coefficient of viscosity behaves differently in liquids compared to gases. In liquids, increasing temperature reduces viscosity because the molecules move more freely. In gases, the situation is reversed; higher temperatures increase viscosity due to greater molecular motion and higher collision rates.

Visualize stirring a pot of soup (a liquid) when it’s hot versus cold. In hot soup, the stirrer moves smoothly due to lower viscosity, while in cold soup, you may need more effort. For gases, imagine air in a hot balloon rising quickly due to lower resistance or viscosity compared to cooler air.

The Sutherland correlation technique gives a relationship between the dynamic viscosity and the temperatures...

This section introduces the Sutherland correlation technique, which provides a method to calculate dynamic viscosity based on temperature. The text explains that coefficients in this equation will vary among different gases and how they can be experimentally determined.

Think of cooking. Just as you adjust the cooking time based on the type of food, here, different gases require different 'settings' or coefficients to determine their viscosity accurately in relation to temperature.

Those fluid flow problems we call Newtonian fluids...We call them non-Newtonian fluids...

Here, the distinction between Newtonian and non-Newtonian fluids is explained. Newtonian fluids have a constant viscosity regardless of the shear rate, while non-Newtonian fluids have a varying viscosity depending on the shear rate, like ketchup that flows easier when shaken.

Consider trying to pour ketchup out of a bottle. At first, it doesn’t flow easily (high viscosity), but if you shake or tap it, it flows quicker (lower viscosity). This demonstrates how some fluids change behavior under stress, unlike water, which has a constant viscosity.

That is what will be cause it. So that because of these effects, the force what will be resultant per unit length...

Surface tension is introduced as a concept that describes the elastic-like force at the surface of fluids. The text highlights how temperature can affect surface tension and explains its role in interactions between liquids and gases or solids.

Picture a small insect walking on water. Its weight is not enough to break the water's surface tension, which allows it to 'stand' on the surface like a stretched membrane. This is a practical demonstration of how surface tension works in real life.

With this I conclude this lecture. Thank you.

This final part of the section reflects on the key concepts discussed through the lecture, summarizing the relationship between shear stress, viscosity, and temperature, as well as the properties of fluids like surface tension and density.

Just as you might summarize a book by recalling its main themes and discoveries, this conclusion ties together the primary takeaways from the lecture, allowing students to recall how viscosity behaves under differing conditions and its practical implications.

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