Surface Tension

 

Have you ever seen small insects floating on the surface of water ? 

This is because water surface acts like a stretched elastic membrane. This phenomenon is  known as surface tension.

 A more scientific defenition for surface tension will be like,"The property of liquid surface that allows it to resist an external force due to cohesive nature of its molecules"( USGS.gov).

Surface tension can be mathematically expressed as T =F/L 

Where F is the force acting on the surface and L is the length along which this force acts

The SI unit for surface tension is Newton/ metre (N/M).

What Causes Surface Tension?

Intermolecular forces such as Van der waals force, draw the liquid particles together. Along the surface, these particles are pulled toward the rest of the liquid.

According to Molecular theory molecule well within the liquid experiences forces equally in all directions resulting in net zero force, Whereas a molecule on the surface experience a net downward force such that the surface acts like a stretched elastic membrane.

 Examples for surface tension

1) Spherical shape of liquid drops

 Due to surface tension liquid surface tries to minimise the surface area,that is why small drops of liquid appear in spherical shape inorder to attain the minimum possible surface area

2) Small insects floating on water

3) Soaps and detergents clean clothes by reducing the surface tension of water.

4) floating a needle on the surface of water

5) Clinical test for jaundice

Inorder to understand more about surface tension the following videos might be useful.

https://youtu.be/zMzqiAuOSz0?si=hIu5de32LdlUeOvx

https://youtu.be/i2TguDlE680?si=4ZTDdL9P32ZqsDku

https://youtu.be/5NCOnr3VSAY?si=SfbqJVHGBiyLcunk