Viscosity and Surface Tension

Name: Viscosity and Surface Tension
Author: StemPy Lab

Honey flows slowly, a raindrop falls at a steady speed, an insect walks on water, and water climbs up in a thin tube. In this course we study the internal friction of a fluid, its viscosity, with Stokes' law and the terminal speed, and the surface tension of a liquid, with surface energy, the pressure inside drops and bubbles, the angle of contact and capillary rise.

3 lessons, about 1 h 15 min3 simulations12 problems6 practice questionsPython in every lesson

Created by StemPy Lab

Course outline (3 lessons)

Lesson 1about 25 min
Viscosity and Stokes' law
Viscosity is a fluid's inner friction: layers sliding past each other drag on one another. The force on a plate over a film is $F = \eta A\dfrac{v}{d}$ , with $\eta$ in pascal seconds. A small sphere feels Stokes' drag $6\pi\eta rv$ , so it falls at a terminal speed $v_t = \dfrac{2r^2(\rho - \sigma)g}{9\eta}$ . Liquids get thinner when warmed; gases get thicker.
1 simulation2 practice questions1 Python program4 problems1 Python lab1 question set
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Lesson 2about 25 min
Surface tension and surface energy
A liquid's surface acts like a stretched skin. Surface tension $S$ is the force per unit length along its surface, or the energy per unit area of new surface, in N/m. A soap film has two surfaces. The pressure inside a drop is higher by $\dfrac{2S}{r}$ , inside a soap bubble by $\dfrac{4S}{r}$ .
1 simulation2 practice questions1 Python program4 problems1 Python lab
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Lesson 3about 25 min
Angle of contact and capillary rise
The angle of contact is the angle between a liquid's surface and a solid where they meet: below $90^\circ$ the liquid wets the solid, above $90^\circ$ it does not. In a thin tube a wetting liquid climbs to $h = \dfrac{2S\cos\theta}{\rho gr}$ ; mercury, with an obtuse angle, is pushed down. Wicks, blotting paper, detergents and waterproofing all depend on this.
1 simulation2 practice questions1 Python program4 problems1 Python lab1 note
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Viscosity, Surface Tension and Capillarity: Practice Paper

20 questions · 40 min

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Viscosity and Surface Tension

Course outline (3 lessons)

Viscosity and Stokes' law

Surface tension and surface energy

Angle of contact and capillary rise

Test Your Learning

Your teacher

Discussion (0)