PHY101 General Physics Lecture 5 - Fluids and Viscosity PDF

General Physics PHY101 Prof. Zakaria. M. Abd El-Fattah Prof. Abdelrazek Bedeer Professor of Solid State Physics Professor of Biophysics Faculty of Science, Galala University & Faculty of Science, Galala University Al-Azhar University zaka...

General Physics PHY101 Prof. Zakaria. M. Abd El-Fattah Prof. Abdelrazek Bedeer Professor of Solid State Physics Professor of Biophysics Faculty of Science, Galala University & Faculty of Science, Galala University Al-Azhar University [email protected] [email protected] [email protected] Lecture5: October 26-28, 2024 Fall 24-25 Lecture 5: Fluids and Viscosity qStates of Matter qFluids: An Ideal Fluid qArchimedes' Principle and Buoyancy Force qViscosity and Stokes Law 2 States of Matter: In this lecture we are concerned about fluids; liquids or gases SOLID LIQUID GAS PLASMA Tightly packed, in a regular pattern Well separated with no regular Vibrate, but do not move from place arrangement. Vibrate and move freely at to place. Solid has a definite volume high speeds. an unconfined gas has and shape neither a definite volume nor a definite shape. Close together with no regular arrangement. Has no definite volume or shape and is Vibrate, move about, and slide past each other. a composed of electrical charged particles liquid has a definite volume but no definite shape. 3 States of Matter: Liquid Gas When dealing with fluid some important quantities are to be considered: Examples: Mass density and Pressure 4 Mass Density 𝜌: High Medium Low 5 Average Pressure P: What if the cube is deeper?! Swimming or diving. 6 Average Pressure P: 7 Average Pressure P: Example 1 8 Average Pressure P: Example 2 9 Archimedes' Principle : Buoyant Forces The magnitude of the buoyant force on an object always equals the weight of the fluid displaced by the object 10 Archimedes' Principle : Buoyant Forces 𝜎 𝜌 𝜎V g mass of the object 11 11 Assignment 2 + Online Quiz 1 Assignment 2: Shall cover topic in Lecture 3-4 - Published on Canvas Tuesday October 29, 2024 - Deadline on Canvas Friday November 1, 2024 Online Quiz: Shall cover topic in Lecture 1-5 - Available ONLINE on Thursday November 7 - Start at 21:00 PM to 21:40 PM 12 Thank You Next Lecture: Fluid Flow and Viscosity + Revision of Classical Mechanics If you need any help write me to: [email protected] [email protected] Or show up at my office: Faculty of Basic Science, Floor 4, Office No. 5 ACKWONLEDGMENT : Prof. Hassan El-Dessouky Prof. Mohammed Emam-Ismail Assoc. Prof. Afaf El-Sayed Fluid Flow : Steady (Laminar), Unsteady, Turbulence The flow is said to be steady, or laminar, if each particle of the fluid follows a smooth path (streamlines) such that the paths of different particles never cross each other. That is the velocity of the fluid is constant in time. Streamlines are tangent to the velocity of the fluid’s particles 14 Fluid Flow : Steady (Laminar), Unsteady, Turbulence The flow is said to be unsteady, if the fluid velocity at a given point changes. The flow is said to be extremely unsteady (Turbulence), if the fluid velocity at a given point changes erratically both in magnitude and direction. 15 Fluid Flow : Ideal Fluid The flow is said to be ideal if the fluid: - Uncompressible: The volume is constant - Undergoes steady/laminar flow: the fluid velocity at a given point is constant. - Has no viscosity: No friction forces between the fluid layers and the walls of containers. The flow of an ideal fluid can be then governed by the Continuity Equation 16 Fluid Flow : The Continuity Equation The continuity equation for ideal fluids states that the product of the area and the fluid speed at all points along a pipe is constant. = Constant = Flow rate (Flux) Q The condition Av = constant is equivalent to the statement that the volume of fluid that enters one end of a tube in a given time interval equals the volume leaving the other end of the tube in the same time interval if no leaks are present. High density of streamlines means higher velocity 17 Fluid Flow : The Continuity Equation Example 18 Fluid Flow : Real Fluids and Viscosity F ext P2 > P1 19 Fluid Flow : Real Fluids and Viscosity To visualize viscous flow in a tube of circular cross section, imagine the fluid to flow in cylindrical layers, or shells. If there were no viscosity, all the layers would move at the same speed. A liquid is more viscous if the cohesive forces between molecules are stronger. The viscosity of a liquid decreases with increasing temperature because the molecules become less tightly bound. Gases, on the other hand, have an increase in viscosity for an increase in temperature. At higher temperatures, the gas molecules move faster and collide more often with each other. 20 Fluid Flow : Viscous Fluids & Drag Force: Stokes Law 21 Fluid Flow : Viscous Fluids & Drag Force: Stokes Law 22 Fluid Flow : Viscous Fluids & Drag Force: Stokes Law In general, a sphere dropped into a viscous liquid experience three forces: Drag Force Physics Lab Buoyancy Force 𝟒 Fd = 𝟔 𝜼 𝝅 𝒓 𝒗 Fb = 𝟑 πr3 𝜎 g Gravity Force 𝟒 Fg = 𝟑 πr3 𝜌 g When the ball reaches constant terminal velocity (zero acceleration): 𝟒 𝟑 𝟒 𝝅𝒓 𝝆𝒈 = 𝝅𝒓𝟑 𝝈𝒈 + 𝟔𝜼𝝅𝒓𝒗 𝟑 𝟑 23 Home Work: 2. A spherical stone of volume 2.7 × 10–4 m3 falls through the air and experiences a drag force of 3 mN at a particular instant. Air has a viscosity of 1.81 × 10-5 Pa s. Calculate the speed of the stone at that instant. a) 222 m/s b) 220 m/s c) 240 m/s d)110 m/s 24  Classical Mechanics: Motion in 1D Lecture 5: Warp Up At this point, you should be familiar with the following: - States of matter - Archimedes' principle - Fluid Flow - Ideal Fluid and Continuity Equation - Viscosity and Stokes Law 𝜎V g 25 mass of the object Assignment 2 + Online Quiz 1 Assignment 2: Shall cover topic in Lecture 3-4 - Published on Canvas Tuesday October 29, 2024 - Deadline on Canvas Friday November 1, 2024 Online Quiz: Shall cover topic in Lecture 1-5 - Available ONLINE on Thursday November 7 - Start at 21:00 PM to 21:40 PM 26 Thank You Next Lecture: Revision of Classical Mechanics If you need any help write me to: [email protected] [email protected] Or show up at my office: Faculty of Basic Science, Floor 4, Office No. 5 ACKWONLEDGMENT : Prof. Hassan El-Dessouky Prof. Mohammed Emam-Ismail Assoc. Prof. Afaf El-Sayed