Question

12. Friction of particles.
(a) A sphere and disk have the same radius. For a given
applied force, which moves faster in flow?
(b) Does a long thin ellipsoid move faster lengthwise or
sideways?

Answer 1

a) for sphere friction coefficien, and for a disk which will move randomly with the flow, the friction coefficient for random moving of disc , ,

Since, 6 =18.85 which is greater than 12, So, friction coefficient fro sphere is high than disk. So

disk will move faster compare to sphere.

b)

For a long thin ellipsoid,b << a,

for lengthwise movement, friction coefficient ,

for sideways movement, friction coefficien ,

Since friction coefficient value for sideways movement is high, so ellipsoid will move faster with lengthwise movement.