(1) Temperature : The surface tension of liquid decreases with rise of temperature. The surface tension of liquid is zero at its boiling point and it vanishes at critical temperature. At critical temperature, intermolecular forces for liquid and gases becomes equal and liquid can expand without any restriction. For small temperature differences, the variation in surface tension with temperature is linear and is given by the relation
\[{{T}_{t}}={{T}_{0}}(1-\alpha \,t)\]
where \[{{T}_{t}}\], \[{{T}_{0}}\] are the surface tensions at \[{{t}^{o}}C\] and \[{{0}^{o}}C\] respectively and a is the temperature coefficient of surface tension. Examples : (i) Hot soup tastes better than the cold soup.
(ii) Machinery parts get jammed in winter.
(2) Impurities : The presence of impurities either on the liquid surface or dissolved in it, considerably affect the surface tension, depending upon the degree of contamination. A highly soluble substance like sodium chloride when dissolved in water, increases the surface tension of water. But the sparingly soluble substances like phenol when dissolved in water, decreases the surface tension of water.
(1) It depends only on the nature of liquid and is independent of the area of surface or length of line considered.
(2) It is a scalar as it has a unique direction which is not to be specified.
(3) Dimension : \[[M{{T}^{-2}}]\]. (Similar to force constant)
(4) Units : N/m (S.I.) and Dyne/cm [C.G.S.]
(5) It is a molecular phenomenon and its root cause is the electromagnetic forces. 
To minimize the depression in the beam, it is designed as I-shaped girder.
(vi) For a beam with circular cross-section depression is given by \[\delta =\frac{W{{L}^{3}}}{12\pi \,{{r}^{4}}Y}\]
(vii) A hollow shaft is stronger than a solid shaft made of same mass, length and material.
Torque required to produce a unit twist in a solid shaft \[{{\tau }_{\text{solid}}}=\frac{\pi \eta {{r}^{4}}}{2l}\] ...(i)
and torque required to produce a unit twist in a hollow shaft \[{{\tau }_{\text{hollow}}}=\frac{\pi \eta (r_{2}^{4}-r_{1}^{4})}{2l}\] ...(ii)
From (i) and (ii), \[\frac{{{\tau }_{\text{hollow}}}}{{{\tau }_{\text{solid}}}}=\frac{r_{2}^{4}-r_{1}^{4}}{{{r}^{4}}}=\frac{(r_{2}^{2}+r_{1}^{2})(r_{2}^{2}-r_{1}^{2})}{{{r}^{4}}}\] ...(iii)
Since two shafts are made from equal volume \[\therefore \] \[\pi {{r}^{2}}l=\pi (r_{2}^{2}-r_{1}^{2})l\]\[\Rightarrow \] \[{{r}^{2}}=r_{2}^{2}-r_{1}^{2}\]
Substituting this value in equation (iii) we get, \[\frac{{{\tau }_{\text{hollow}}}}{{{\tau }_{\text{solid}}}}=\frac{r_{2}^{2}+r_{1}^{2}}{{{r}^{2}}}>1\] \[\therefore \] \[{{\tau }_{\text{hollow}}}>{{\tau }_{\text{solid}}}\]
i.e., the torque required to twist a hollow shaft is greater than the torque necessary to twist a solid shaft of the same mass, length and material through the same angle. Hence, a hollow shaft is stronger than a solid shaft. 
If we have two tyres of rubber having different hysteresis loop then rubber B should be used for making the car tyres. It is because of the reason that area under the curve i.e. work done in case of rubber B is lesser and hence the car tyre will not get excessively heated and rubber A should be used to absorb vibration of the machinery because of the large area of the curve, a large amount of vibrational energy can be dissipated. 
