[Music] hello friends welcome to science for juniors with me SRK and my lab assistant Benny no open e can you get me those files kept on that table oh sure professor the world of science is so wonderful what happened oh oh here's your files are you alright yes I guess my shoes are too slippery hmm slippery shoes reduce the friction and make you fall and that friction what's friction and what does it have to do with me falling there well friction is a force that ensures that you don't slip why don't we go to the virtual world and learn in detail about friction let's begin the module on friction what is it with what we see athletes are required to run at top speeds their shoe soles have specially designed patterns underneath on the soles why would they need to wear rigged soles shoes can't they run really fast wearing simple canvas shoes let's find out the answer to this question in the module on friction what is it where we study friction and its causes what factors does it depend upon let's consider a box that appears to be smooth macroscopically any surface no matter how smooth it appears has large number of irregularities on it at microscopic level the moment any surface B is placed on a interlocking of irregularities takes place these interlocked surfaces will resist any tendency to move due to the interlocking of irregularities there appears a force that always opposes the motion between the two surfaces this opposing force is called friction now let's see what does this frictional force depend upon smoother surfaces will offer less friction for example a rubber wiper sliding on the glass surface feels very less friction that's because here the two surfaces in contact are very smooth on the other hand a wooden stool kept over a rough cemented floor will feel more friction friction depends upon the smoothness of the two surfaces in contact through the surfaces in contact offer less friction rougher surfaces in contact offer more friction it is easier to pull a lighter object it is difficult to pull a heavier object it is easier to pull lighter weight object than heavier weight object as the lighter body experiences lesser friction friction is more for heavier bodies than for lighter bodies so remember that friction on a body depends firstly on the extent of smoothness of the two surfaces in contact smoother surfaces will experience lesser friction rougher surfaces will experience more friction secondly heavier bodies experience more friction than lighter bodies so Binney now you understand what is friction yes um friction opposes the motion between two surfaces right can I ask something I was just wondering what all could be possible without having to worry about friction yeah you may suggest some examples which you think don't require any friction okay looking at oneself in the mirror doesn't require friction yes you are right Vinny very expected example from you next making sure parties won't require friction yes of course it requires friction or else the chapatis will keep slipping Leidy a matchstick I'm sure has got nothing to do with friction of course it's got everything to do with friction you can't light a matchstick without the frictional force between the stick and the surface of the matchbox on which it is rubbed against oh really before I actually begin to appreciate friction I still don't understand what it had to do with me slipping well it had a lot to do Benny let's first go to the virtual world and understand how friction assists us in walking oh it does yes now let's hit the virtual world ever wondered that a friction always opposes the motion between two surfaces in contact then how do we walk surprisingly we walk because of friction as we try to take a step forward we push a foot backward friction holds our shoe to the ground allowing us to take the next step forward in other words friction assist us in walking it's time to answer the question raised at the beginning of this module athletes prefer rigged shoes over the canvas shoes this is because they would require rigged soles which being rougher than canvas soles will offer greater friction greater friction offered by rigged shoes will assist athletes to run at high speeds let's take an example the box lives here with largest face down the little girl fails to pull through the box now lies with smallest facedown will the Box move now the answer is no the opposing friction that the little girl has to overcome is the same in both the cases friction does not depend on the area of contact as a weight of the box remains the same in both the cases the opposing friction experienced will remain the same so far the same force applied by the girl the box will fail to move oh now I understand why I fell these slippery shoes have less friction with the floor when I walk exactly Benny you are becoming smarter huh what was that Benny why did you shout at the top of your voice if you keep shouting at those decimals my ears will stop functioning anyways so why did you shout oh I was just wondering it will be easier to drag the chair when I'm sitting on it rather than you sitting on it well yes as you learn just now friction depends upon the weight of the body Moe is the weight of the body greater will be the friction opposing proves what Benny to you that can't be as funny as you are trying to make it out hmm I was wondering how the world would have been if the force of friction didn't exist oh you want to know that yes of course then let's go to the virtual world and find out let's challenge our brains what if friction vanishes the life would be a difficult place to live without friction in action all of us would be slipping and sliding all the time nobody will be able to walk or run without friction athletes can no longer run on the racetracks they will simply slip on the erase tracks no races man wouldn't have made fire hundreds of years ago rubbing stones involve friction in the absence of friction mankind would have never discovered fire man would have never evolved to the world we see today oh my god it will be impossible for us to live without the existence of the force of friction absolutely imagine all of us just lipping all the time in a vain effort oh my god I can imagine that you have got quite an imagination Vinnie I must say that Thank You professor so now you understand the importance of friction well oh yes to a large extent professor ah the but again tell me what is it oh nothing I mean I was just thinking can you give me some more specific examples of friction in daily life oh of course Benny why not in fact that will help my friends sitting there at home and learning from us understand the concept of friction better and realize its importance let's check out our do you know section for this do you know that friction plays an essential role in our daily life like what like in writing and erasing how does friction happen that writing with a pencil requires friction you could not hold a pencil in your hand without friction it would slip out when you try to hold it too right oh yes even the graphite pencil lead would not make a mark on the paper without friction similarly a pencil eraser uses friction to rub off mistakes written by the pencil led rubbing by an eraser wears out the eraser due to friction while the particles borne off gather up the pencil led from the paper Wow never thought of that similarly your car would not move if it wasn't for the friction of the tires against the street with no friction the tires would just spin oh yes then we could not stop also without the friction of the brakes and the tires all right let's have a quick recap friction is a force that acts between any two surfaces in contact with a tendency to move friction always opposes the motion between the two surfaces in contact frictional force depends on the weight of the body frictional force is independent of the area in contact Wow I never ever realized there are so many important forces working around us that make our life so easy yes Benny this whole universe is full of such wonderful forces and mysteries of life Wow thanks for explaining professor you are always welcome Vinnie and so are my dear friends sitting there anyways time for us to say goodbye to a dear friends but we will see you again soon till then keep exploring the wonder world of science [Music] [Music]