Fluid Nature
Fluid:Gas and liquid that are compressible called fluids.Fluids are those that can be pressed to change their volume and applies interactive force within their molecules.Example :water and all gases are said to be fluid.
Thrust: Fluids always exert a force on each other and on the surface of container.The molecules flow in the random direction in the container and they strikes with each other and also with the sides of container .The force with which they strikes on the sides of container is measured as thrust of liquid.Force applied on per unit area of walls of container is called thrust. It is similar as pressure.
Few of applications of pressure are as follows:
1.A sharp nail is required to stuck into the wall .It is because the sharp edge will easily stuck into wall by small pressure as compare to nail with broad edge.
2. Bags with broad strips are provided so as to reduce the pressure on the shoulders because due to wide strip the force spreads on the area of strip and less pressure applied.
3. If we walk bare footed on pebbles these pinch in foot because due to their sharp edges they applies more force on foot and pinch.
Surface Tension :
Surface tension is the property of liquid of stretching its upper surface to form a membrane. In actual as we have discussed liquid molecules applies force on each other . Molecules present in the middle of liquid are in equilibrium as these are attracted by molecules in all directions and no net force is applied on them.But molecules present on the upper surface of the liquid are attracted by the molecules present in the lower molecules and there are no molecules in above of them to attract them .Hence they come in tension by lower molecules and stretched up to form a membrane.See in the below diagram .

Applications of Surface Tension :

Rain drops always falls in spherical shape:it is because due to surface tension liquid drop tends to occupy smallest area. As spherical shape has smallest area so liquid drop acquires spherical shape.

When we dip paint brush in water or in any liquid it spreads out but when we take it out it contracts .It is so because when it is in water its bristles are attracted by all over molecules so it spreads  but when it is taken out The molecules inside the bristles tends to attract the bristles inside due to surface tension and it contracts.