The force per unit length or energy per unit area on the surface of liquid is called “Surface Tension.”
Surface Tension = Force / Length or Energy / Area
The unit of surface tension is N/m or J/m2 in MKS system.
The molecules present within the body of liquid are subjected by forces is all direction. The force from left is cancelled by the force from right while the force from bottom is balanced by force from top. But the molecules present at the surface of liquid are subjected by force in three directions. The force from top is canceled by the force from right but there is no force to balance the downward force. Hence a downward pull produced on the surface molecules called “Surface Tension”.
FACTOR EFFECTING SURFACE TENSION:
By increasing the Temperature the KE as well as the motion of particles of liquid increases so that spaces between them also increases as a result surface tension decreases.
Greater force of attraction between particles of liquid greater will be the downward pull on the surface molecule so that greater will be the surface tension.