 Hello friends and welcome to another session on physics and we are discussing a very interesting topic called force right and so far we have seen what force was and we also saw its unit SI unit and then we also talked about its vector nature right now today we are going to explore a little bit more about force today we are going to talk about what types of forces we come across in our day-to-day life so on your screen you can see it some cases some examples from our day-to-day life which we have picked up and we are going to discuss this one by one so if you look at the first footage which is going on you can see a foot bridge right so you can see there is a person who is carrying a camera and he is moving on the bridge now you can also see that there is no support underneath so why is this bridge not falling so you can see that the bridge is suspended using some ropes now this you keep in mind that the bridge is held by ropes and hence the bridge is not collapsing under the influence of gravity so hence here the bridge is suspended by the rope now in the next footage you can see a shipyard basically this is a cargo or a support basically and you can see that ship are being loaded with you know there is a cargo operation going on so containers are being lifted up by a huge movable crane now you can again observe that the crane is lifting the load the container right and it is again if you see there are there are lots of ropes going over some pulleys and the rope is being pulled and rope is attached to the container and hence the container is going up now look at this one this is a bicycle and in the bicycle you all ride a bicycle and you would have observed in the rear side rear wheel there is a sprocket and the chain runs over it and once you apply force on the pedal the pedal pulls the chain and the chain then in turn helps in rotating the wheel so here again the chain is connected to the wheel is it now in the next one you can see a huge bridge over a river and the bridge if you look at the construction of the bridge it is suspended again by lots of ropes in this case these are ropes made up of steel but still the pillars are connected to the ropes and the ropes are pulling the bridges bridge up right so that's another another footage and the next one you can see someone you know making some keystrokes and she is trying to type in something so here again her fingers are you know touching the the keyboard right now come to this one this is more much familiar so those who are into music they will know that to play the guitar you have to you know pluck the strings and the strings then vibrate and then some music comes out of that guitar similarly while playing a drum you have to hit the drum skin using a stick so again you have to touch the drum to produce the sound now why are we discussing all these you know cases so if you see in all of them whether it is a footbridge whether it is a container being pulled by a crane whether it is a bicycle chain whether there's a bridge being suspended from ropes or someone striking the keyboard or someone playing the band or you know the guitar in every case you can observe that some bit of force is being applied through contact right so in the case of footbridge there was a contact of rope with the bridge in the container case there is a contact of the ropes again with the container in the bicycle the chain is in contact with the the wheel in the bridge again there are lots of steel ropes which are in contact with the bridge in the computer keyboard also to press a key you have to you know bring your fingers in contact with the keys isn't it and in the case of that guitar or the drum again someone has to establish a contact to create some music now this is what i was trying to emphasize on so for all these in all these cases we need to apply or create a contact to apply force isn't it so in the last few sessions we observed what force is today we are trying to classify or understand how forces are you know bring or how forces are brought into effect or how you can apply force to see some effect so that's what all these you know example videos you know showed you now let us have a look on another type of cases so in this video you can see few people they are probably you know very courageous that they are taking or they are jumping from a high cliff into the water underneath right now in this case you must think why is this guy or this person is freely falling towards the water there is no contact there is no one who is pushing there is no one you know uh visibly in contact with this person so all these people who are diving must be in touch with something or in contact with something which is invisible right so here who is pulling them down clearly the earth's gravity is pulling them down but earth isn't earth is not in contact with these people that means there is something invisible which is pulling them down now later on you will see that there is something which is called gravitational field which is in contact with these people but as of now if you can see forces can be applied from a distance that is the people who are jumping are away from the surface of the earth still earth is able to pull them down so hence that means these kind of forces also exist where no contact is needed for the force to be applied in the second case if you look very closely and i would encourage everyone to you know do this experiment what you can do is you know get some bits of paper put them on a table then take a ruler a plastic one and then rub them rub the ruler against your dry hair and most of you would have done this in the past you know in your physics experiment lab now once you you know rub this ruler plastic ruler against the dry hair and then bring it very close to these pieces these pieces of paper you can see that they are being pulled towards the ruler now again there is no contact isn't it so the ruler is not touching the pieces of the paper but still they are able or the ruler is able to pull them towards itself how is that happening so this was again you know given by another famous scientist coulomb and he suggested that there is something called electrostatic force of attraction between positive and negative charges so you'd have anyways known by now that there are two types of charges existing in nature positive and negative and positive charge and negative charge attract each other and the like charges repel each other that is positive positive repel negative negative repel but positive and negative charges attract each other now again to effect this attraction that is for the force to be applied here there is no no contact needed okay so this is another example where no contact is needed for the force to be applied similarly all of you would have played with magnets magnets again pull each other without any contact established right so this is another another type of force where contact is not needed now with all these discussions and what do we conclude we conclude that in nature we can clearly see two types of forces one where the contact is needed for example if you push want to push the table or open the book or open the door close the door write on a paper everywhere contact is needed to apply the force but there are few cases where force is not required to or sorry their contact is not needed to be established for the force to act examples a freely falling body a magnet attracting another iron piece or another magnet a positive charge attracting a negative charge and things like that so are these only types of non-contact forces no there are certain more types of you know non-contact forces which you will come across very soon and these are nuclear forces we can strong we will study about them in the next session so we will be talking about more on non-contact based forces in a deeper detail in the next session but to summarize the discussion of this particular session we we conclude that there are two types of forces which we can observe one which require contact to be established for the force to be applied and another one where no contact is needed for the force to be applied