Question

Of the two lubricants A and B for a machine, A has a co-efficient of viscosity slightly greater than that of B. Which would you prefer in summer and winter?

Answer 1

Viscosity and viscosity coefficient:

1. Viscosity-It is a property of a fluid. It is defined as the degree to which a fluid resists the flow under an applied force It gives its measure of thickness. Eg Sugar syrup is more viscous than water.
2. Viscosity coefficient- Viscosity is measured in terms of the coefficient of viscosity. It is constant for every liquid. The coefficient of viscosity decreases with an increase in temperature. To prove this point, we have taken an example of viscosity of water vs increase in the temperature graph.

$$\begin{gathered} V=\frac{\pi \Delta P{r}^{4}t}{8\eta L} \\ \eta =\frac{\pi \Delta P{r}^{4}t}{8VL} \end{gathered}$$

We know,

$\log \eta =\frac{A}{T}+B$

$V\to$volume of the liquid.

$∆P\to$change in pressure.

$r\to$radius of vessel.

$\eta \to$coefficient of viscosity.

$t\to$time

$L\to$length of the vessel

$T\to$Temperature

Explanation:

1. It is mentioned that sample A has a coefficient of viscosity slightly greater than sample B.
2. Sample A will be preferred in summers as the temperature is high and due to this coefficient of viscosity will decrease as they are inversely proportional.
3. Sample B will be preferred in winters as the temperature is low and due to this coefficient of viscosity will increase.

We should use sample A in summers and sample B in winters as the coefficient of viscosity is inversely proportional to temperature.