Why do machine parts become sticky in winter?

$A$ river $10\,m$ deep is flowing at $5\,m/s$. The shearing stress between horizontal layers of the river is :- $(\eta = 10^{-3}\,SI\,unit)$

Is viscosity a vector or a scalar?

$A$ metal plate of area $10^{-2} \,m^2$ rests on a layer of castor oil, $2 \times 10^{-3} \,m$ thick, whose coefficient of viscosity is $1.55 \,Ns\, m^{-2}$. The approximate horizontal force required to move the plate with a uniform speed of $3 \times 10^{-2} \,ms^{-1}$ is (in $N$)

$A$ liquid having a coefficient of viscosity $0.02 \, \text{decapoise}$ is filled in a container of cross-sectional area $20 \, m^2$. If the viscous drag between two adjacent layers in flowing is $1 \, N$, then the velocity gradient is ........ $s^{-1}$.

$A$ thin square plate of side $2\ m$ is moving at the interface of two very viscous liquids of viscosities $\eta_1 = 1 \text{ poise}$ and $\eta_2 = 4 \text{ poise}$ respectively, as shown in the figure. Assume a linear velocity distribution in each fluid. The liquids are contained between two fixed plates. $h_1 + h_2 = 3\ m$. $A$ force $F$ is required to move the square plate with a uniform velocity $10\ m/s$ horizontally. The value of the minimum applied force will be ........ $N$.