SUBJECT: PHYSICS
CLASS: SS 1
DATE:
TERM: 1st TERM
REFERENCE BOOKS
WEEK TEN
TOPIC: VISCOSITY
CONTENT
MEANING OF VISCOSITY
Viscosity is the internal friction which exists between layers of the molecules of a fluid (liquid or gas) in motion. The viscosity of a fluid can also be defined as the measure of how resistive the fluid is to flow. It is a vector quantity & measured in pascal-seconds(pa.s). It can be defined mathematically as the ratio of the shearing stress to the velocity gradient in a fluid
Viscosity (Å) = Force
Area x Velocity gradient ……………………………………….1.
Velocity gradient = velocity
Length …………………………………………………2
W = U + V
W – U- V = 0 ……………………………………………………………3.
V = W – U (apparent or effective weight) where V-viscous force, W- weight, U- upthrust
NB : Substances with low viscosity include water, kerosene, petrol, ethanol. Those with high viscosity are glue, syrup, grease, glycerine etc
Experiment to Determine the Terminal Velocity of a Steel Ball Falling Through a Fluid
Aim: To determine the terminal velocity of a steel ball falling in through a jar of glycerin
Apparatus: steel ball, cylindrical calibrated jar, glycerine
Diagram:
Procedure: Set-up the apparatus as shown above & gently drop the steel ball in the jar of glycerin
Observation: It will be observed that the ball is accelerating in the liquid. Also the time taken for the ball to move from A-B will be different from B-C and so on. A time will be reached when the ball will be moving at a constant speed or velocity. It is that point that terminal velocity is experience.
Graph :
Conclusion: Terminal velocity is attained when W = V + U. At a point when the ball is moving at a constant speed through the glycerine.
Precaution: 1. The steel ball should be dropped gently on the liquid 2. Experiment should be done under constant temperature 3. Avoid error of measurement when taken the reading.
NB: Terminal velocity is the maximum velocity of an object when the viscous force due to motion of the object equals the apparent (effective) weight of the object in the fluid where there is no longer net force on the object.
Drag force is the force that keeps the object continuously moving after the terminal velocity has been attained.
Stokes’ Law state that at the terminal velocity, the upward frictional force (F) = 6Π ÅrV
Where F- Frictional/Drag force, Å- viscosity, r- radius of sphere, Vt- Terminal velocity
EVALUATION
Factors Affecting Viscosity
Effect of Viscosity
Application of Viscosity
EVALUATION
GENERAL EVALUATION
READING ASSIGNMENT
New school physics by M.W.Anyakoha,Phd.Pg 105 – 107
WEEKEND ASSIGNMENT
THEORY
NB: A liquid is said to be VISCOSTATIC if its viscosity does not change (appreciably) with change in temperature.
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