let us talk about significance of surface

tension. to understand the significance of surface tension lets consider a container

. in which , say a liquid is filled. say this is a container in which liquid is filled up

to the top. and in this situation we already discuss that, every point on surface of liquid,

will behave as a if it is under tension . or every point will be experiencing an outward

force of attraction by its neighboring particles. now in this situation if i consider a hypothetical

line say this line ay-b on the. liquid surface . then every particle on this line will be

experiencing the force on left-and-right side. of this line. so we can say the resulting

effect of all these forces will be acting in a direction normal to the line. so we can

say in this situation the total force due to surface tension acting on the line will

be zero as it is being pulled by equal forces in opposite direction. but if i talk about

a line, which is there on the. edge of the container. and only on one side of this container.

only on one side of the edge as liquid is present and on the other side there is no

liquid. this line will be experiencing the force in the direction . only along the surface

of liquid. so we can say net force due to surface tension on this line say this line

is x-y it will be nonzero . so using surface tension we can find out the total force. for

this purpose we need to give a mathematical . significance or an analytical significance

for surface tension. and its numerical definition i’ll right , so very carefully you just

noted down . here numerically we can say . surface tension. is. numerically defined as. the force

acting. per unit length. of a, hypothetical line. drawn. on a liquid surface. normal to

it. in other direction. here we can say for hypothetical line is drawn. and it experiences

a force net force f and f on the two sides and say its length is l. so here we can say

. the surface tension of liquid. can be given as, t, t is the symbol we use to denote a

surface tension for the liquid it can be given as f upon l. and its unit we can write as

newton per meter obviously . and using this relation if we wish to find out the force

acting , on line in one direction , then we can say if this line is of length l-one we

can say the total force f-one acting on it will be t l-one. if t is the surface tension

of the liquid as force in either direction can be given as . the product of surface tension

in the length of the line on which it is acting. similar analysis we can , understand here

with help of this situation here you can see , if there is wire frame on which there is

a soap film. if we place a, loop of a thread on the soap film it’ll be arbitrary in shape.

and say if we just pick the soap film between the loop by a needle as you can see here . the

force of surface tension will start acting on the loop segments in outward direction

where liquid exist. and like now there is no film in between so force can not be balanced

, earlier when the film was there inside also the force on the two sides were balanced . and

the loop were in arbitrary shape. now due to this prick, the inner film will burst and

, only outer film exist and we can see , due to the forces automatically it is pulled in

outward direction and finally the loop will take a shape of a circle. because we can see

here if outward forces are acting on the loop it will have a tendency to acquire a shape

in which , all the forces will balanced, and that’s why it’ll take, the shape of a

circle. this experiment you can also perform at your home. and understand and this is the

very good experiment to understand . how the force of surface tension act on a line, or

a segment, on which only one side , the film or liquid surface exist .

really a nice explanation sir. the experiment made everything clear. thank you very much sir

Sir, in that experiment how can we calculate tension across the loop thread after it forms circle?

sir…one of my book says that free surface behaves as an elastic membrane trying to reduce its surface area to minimize its potential energy and gain stability.this proper is called surface tension ….So i have doubt that if it reduces its surface area than why its equal to work done in increasing surface area..???

sir why we consider a hypothetical line why not we consider and thing else for eg triangle and sir is the line u had considered is the straight line water molecules or any other liquid plz elaborate

why is it not moving if net force is not equal to 0?

Sir i am having a silly doubt!..in starting of the chapter…we said that the molecules due to their contact have contact forces causing a molecule to have net force 0 but inward pressure….so similarly here at line XY (1:52)..the net force should be on left i.e. repulsive not attractive.plz clear it!..i am confused

Sir I am having doubt that why we subtract Pexcess from P atm when we study ascent formula?

More advanced illustration on fluids

Great work sir

Thanks a lot for this quality education.

Sir, if a net force on edge line is acting, then how is it in equilibrium?

For all those who want to see soap film and thread experiment :

https://youtu.be/e0fhh1830Kc

sir what is soap film

Your voice is pathetic and distracting

Sir , I have a doubt for line AB surface tension should be 0 right because net force is 0 sir? But you wrote t= F/L plz elaborate