A molecule in the interior of a liquid is attracted in all directions because it is surrounded by molecules equally in all directions. However, the molecules at the surface of the liquid are attracted sideways and downwards but not upwards. The cohesion or tension of molecules at the surface, resulting from imbalance of forces acting on them, convert the surface to act as though covered with a film or skin.
This, phenomenon is known as surface tension. Surface tension can be demonstrated by carefully horizontally placing needle at the surface of the water where it will float due to the forces of surface tension.Surface tension is expressed is dynes per centimeter (dynes/cm). In simple words surface tension is defined as the force in dynes acting at right angles to any line,1 cm of length on the surface of a liquid.
Surface tension in milk can be measured any of the two methods:
i)Ring Detachment or Tensiometer method: This is based upon the principle of force required to pull a metal ring free from the surface of a liquid.
ii) Drop Weight method: Here the number of drops formed when a given amount of liquid is allowed to fall from a pipette is measured. The instrument used to measure drop weight is known as stalagmometer. It consists of a glass tube with a uniform diameter of 1-3 mm with a small bulb which is sharply grounded so that the liquid drops from the tube in an almost spherical form. The tip of the tube can be enclosed in a circulating water bath to control the temperature. Droplets falling from the tube are collected and weighed.
The Surface tension of milk: Surface tension of milk falls in the range of 40 to 60 dynes/cm. A value of 50 dynes is commonly taken as surface tension of milk at 20 0 C. Water has a surface tension of 72.75 dynes/cm at 20 0 C. The lower value of milk compared to water is due to substances which lowers the surface tension of milk. Notably, these include fat and protein. Fat significantly lowers the surface tension of milk as cream has a surface tension value of 39-40 dynes/cm. Lipolysis also lowers down the surface tension of milk.
This, phenomenon is known as surface tension. Surface tension can be demonstrated by carefully horizontally placing needle at the surface of the water where it will float due to the forces of surface tension.Surface tension is expressed is dynes per centimeter (dynes/cm). In simple words surface tension is defined as the force in dynes acting at right angles to any line,1 cm of length on the surface of a liquid.
Surface tension in milk can be measured any of the two methods:
i)Ring Detachment or Tensiometer method: This is based upon the principle of force required to pull a metal ring free from the surface of a liquid.
ii) Drop Weight method: Here the number of drops formed when a given amount of liquid is allowed to fall from a pipette is measured. The instrument used to measure drop weight is known as stalagmometer. It consists of a glass tube with a uniform diameter of 1-3 mm with a small bulb which is sharply grounded so that the liquid drops from the tube in an almost spherical form. The tip of the tube can be enclosed in a circulating water bath to control the temperature. Droplets falling from the tube are collected and weighed.
The Surface tension of milk: Surface tension of milk falls in the range of 40 to 60 dynes/cm. A value of 50 dynes is commonly taken as surface tension of milk at 20 0 C. Water has a surface tension of 72.75 dynes/cm at 20 0 C. The lower value of milk compared to water is due to substances which lowers the surface tension of milk. Notably, these include fat and protein. Fat significantly lowers the surface tension of milk as cream has a surface tension value of 39-40 dynes/cm. Lipolysis also lowers down the surface tension of milk.
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