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Digital Textbook
VISCOSITY
Name of the teacher :Najma M U
Date : 20/5/22
Department : Physical Science
Class : 9th
Subject : Physics
Duration : 40 minutes
Unit : Forces in Liquids
Topic : Viscous Force
Instructional Objectives
To understand about the viscous force and viscosity in fluids
To classify liquids as Viscous and mobile liquids
To understand the effect of temperature on Viscosity
To utilise viscosity in daily life
What is Viscous force?
The resistive force of one layer to the flow of another layer of a liquid is called Viscous Force.It is the internal frictional force existing with in the liquid which opposes the relative motion between the layers.
What is Viscosity?
Most fluids offer some resistance to motion, and we call this resistance “viscosity.” Viscosity arises when there is relative motion between layers of the fluid. More precisely, it measures resistance to flow arising due to the internal friction between the fluid layers as they slip past one another when fluid flows. Viscosity can also be thought of as a measure of a fluid's thickness or its resistance to objects passing through it.
Definition : Viscosity is a measure of a fluid’s resistance to flow. The special property of liquid to oppose this relative motion of layers between the liquid is called Viscosity.As viscosity increases speed of layer decreases.
The SI unit of viscosity is poiseiulle (PI). Its other units are newton-second per square metre (N s m-2) or pascal-second (Pa s.) The dimensional formula of viscosity is [ML-1T-1].
Mobile and Viscous liquids
Mobile and Viscous liquids All liquids do not flow alike. Liquids of greater viscosity are viscous liquids and those of very lower viscosity are the mobile liquids.
Viscous liquids will flow very slowly and mobile liquids will flow easily
Examples
• Viscous Liquids: Honey,gelatin, glycerine, oil, etc
• Mobile liquids :Water, petrol, keroscene, rose water, etc
Effect of Temperature on Viscosity
When temperature is given to a liquid, the intermolecular force of attraction decreases. As a result viscous force decreases and viscosity decreases. As temperature increases, viscosity decreases.As temperature decreases, viscosity iTemperature
Application of Viscosity and Temperature
When shocked, Body temperature will drop suddenly.It will enhance the viscosity of blood and blood can’t flow through the vessel, which will cause Heart attack. By rubbing Body temperature increases, viscosity of blood decreases and will flow smoother.
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