Question

Fill in the blanks using the word(s) from the list appended with each statement.
(a) Surface tension of liquids generally ....... with temperatures. (increases / decreases)
(b) Viscosity of gases ........ with temperature, whereas viscosity of liquids ....... with temperature (increases / decreases)
(c) For solids with elastic modulus of rigidity, the shearing force is proportional to ....... , while for fluids it is proportional to ....... (shear strain / rate of shear strain)
(d) For a fluid in a steady flow, the increase in flow speed at a constriction follows (conservation of mass / Bernoullis principle)
(e) For the model of a plane in a wind tunnel, turbulence occurs at a ....... speed for turbulence for an actual plane (greater / smaller)

Answer 1

(a) Surface tension of liquids generally decreases with temperatures. As temperature increases, the kinetic energy of molecules increases and they overcome the attractive forces.

(b) $\eta$ of gases increase and $\eta$ of liquids decrease with an increases in temperature.

As temperature increases, the average speed of molecules in a liquid also increase and as a result, they spend less time with their "neighbors." Therefore, as temperature increases, the average intermolecular forces decrease and the molecules are able to interact without being "weighed down" by one another. However, the viscosity of a gas increases as temperature increases because there is an increase in frequency of intermolecular collisions at higher temperatures. Since the molecules are flying around in the void most of the time, any increase in the contact they have with one another will increase the intermolecular force which will ultimately lead to a disability for the whole substance to move.

(c) For solids with elastic modulus of rigidity, the shearing force is proportional to Shear Strain

$F=GϵA$
For fluids, it is proportional to the rate of shear strain
$F=\mu \frac{du}{dy}$

(d) Conservation of mass will always be followed and since the flow is steady, even Bernoullis principle would be followed.

(e) Greater

Since in an actual environment, the external disturbances also come into picture that cannot be introduced in a lab.