i) The rolling friction is smaller than sliding friction
ii) By using ball bearings sliding friction is replaced by rolling friction
iii) A ball bearing is used in a cycle hub to reduce friction.

Pascal's law states that the pressure applied at any point of a liquid at rest, in a closed system will be distributed equally through all directions of the liquid.
Applications of Pascal's law:
i) In an automobile service stations, the vehicles are lifted upward using the hydraulic lift, which works as per Pascal's law.
ii) Automobile brake system works according to Pascal's law.
iii) The hydraulic press is used to make the compressed bundles of cloth or cotton so as to occupy less space.

Ways to minimise friction
(i) By applying lubricants like grease and cocount oil.
(ii) By using ball bearing we can change sliding friction to rolling friction
(ii) By smoothening the surface of contact of the moving bodies rather than irregular surfaces.

We cannot use water as a barometric liquid.
Difficulties of constructing a water barometer
i) Water has less density than mercury. Hence the fluid column of water barometer should be atleast 10 metre. This will be 13.6 times more than that of a mercury barometer.
ii) Vapor pressure of mercury is very low. So, very minute variation in atmospheric pressure can be accurately measured. It is not possible in water barometer.
iii) The freezing point of water is 0°C. So, water barometer cannot be used to measure atmospheric pressure at temperatures lower than 0°C.

While travelling in an aeroplane atmospheric pressure decreases with increasing altitude. So pressure inside the aeroplane can also decreases. The pressure inside the fountain pen is more compared to its surrounding Due to varying pressure, the ink gets spilled. Due to ink spillage, fountain pens are not advisable to use while travelling in an aeroplane.