Viscosity

CONTENT

• Meaning of Viscosity
• Experiment to Determine the Terminal Velocity of a Steel Ball Falling  in a Fluid
• Factors Affecting Viscosity
• Effect of Viscosity
• Application of Viscosity

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

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 ŋrV

Where F- Frictional/Drag force, ŋ- viscosity, r- radius of sphere, V_t–  Terminal velocity

EVALUATION

1. Derive the dimension of viscosity.

2.         Describe an experiment to determine the terminal velocity of a steel ball falling in a fluid.

Factors Affecting Viscosity

1. Viscosity varies with material (viscosity is a property of material)
2. The viscosity of simple liquids (a) decreases with increasing temperature (b) increases under very high pressure
3. The viscosity of gases (a) increases with increasing temperature (b) is independent of pressure & density

Effect of Viscosity

1. Viscosity is responsible for different rate of fluid flow.
2. Viscosity affect motion of body in fluid.

Application of Viscosity

1. It is use as a lubricant.
2. The knowledge of viscous drag/drag force is applied in the design of ship & aircraft.
3. Use to estimate the enlarge size of particles.

EVALUATION

1. State two effects of viscosity.
2. State two applications of viscosity.

GENERAL EVALUATION

1.   What is viscosity?
2.   What is terminal velocity?
3.   State two(2) substances with high viscosity.
4.   State Stoke’s law.
5.   What is a viscostatic substance?

READING ASSIGNMENT

New school physics by M.W.Anyakoha,Phd.Pg  105 – 107

WEEKEND ASSIGNMENT

1. Viscosity opposes motion of an object in (a) solid (b) liquid only(c) gas only (d) liquid & gas
2. The SI unit of velocity gradient is (a) m/s (b) s^-1 (c)  m/s² (d) ms
3. Terminal velocity is attained when (a) w + v = u (b) w = v – u (c) w + u = v (d) w = v + u
4. The following are vector quantities except (a) friction (b) viscosity (c) upthrust (d) pressure
5. Friction and viscosity are similar but not the same.  True/False

THEORY

1. Explain viscosity.
2. Describe an experiment to determine the terminal velocity of a steel ball falling in a fluid.

NB: A liquid is said to be VISCOSTATIC if its viscosity does not change (appreciably) with change in temperature.