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Current time:0:00Total duration:10:17

Video transcript

have you seen these people who sleep on a bed full of nails and to make things more dramatic who have an assistant to hammer on them why doesn't it hurt or have you wondered why military tanks have these chains why don't they just have wheels like any other normal vehicles now these two things might seem unrelated but they can be answered by using one single concept of pressure and so in this video let's explore what pressure is to understand pressure let's ask some more questions but this time a little day-to-day life for example when you hammer onto a nail then it can punch her this wooden board right but what if you were to keep the nail of this way and let's say you put the same amount of force do you think now it'll be able to punch her through no right it won't but why well you might say well if you want to punch her through it you need to keep that pointed end over there but why think about this let's take another question if you want to chop a tomato you can easily do that by using a knife but instead let's say used a finger and you put the same force as before now you can't chop it again why even though you're putting the same force as before why can't you chop this time well again you might say well that's because your knife is very sharp and our fingers aren't and so you cut something or punch or something it's important that it has to be very sharp or very pointy but why well let's look at these examples a little bit more carefully so if you take the hammer example whether you keep the nail this way or this way if you bang on this nail with the same force let's say then in both these cases the male will start putting a force on the board and if you bank with the same force you bang with the same force then they also put the same force on the board right but over here because it is very pointy the contact area is so small and as a result all the force gets concentrated into the tiny spot tiny area but over here because the contact area is big much bigger compared to over here that force gets divided over that large area and it starts acting over that large area and as a result if you now compare the amount of force that appears on the same spot as before look that force has reduced significantly because it got divided and that's why it's harder to punch her through over here and the same thing will happen in the tomato case as well when you use a knife and put a force and all that force gets concentrated into a very tiny area because the knife is very sharp very tiny area but because your finger is not so sharp the base area of your finger is so why it's so large compared to the knife that entire force gets divided over a large area and as a result the amount of force that appears on the same slice of the tomato as before is very significantly small and so it seems that if you want to cut something or if you want to punch or something then it's not just the force that matters but that force has to be very concentrated how concentrated that force is that's what matters and that's what we call pressure pressure can be thought of as how concentrated your force is and how do we calculate it well just like over here we saw that we are basically calculating how much the force gets divided over the area mathematically also pressure P is calculated as the force divided by the area so in both these cases when the objects are very sharp the contact area is very small and so the pressure that the experience is large and that's why they're able to cut and punch it through on the other hand if the contact area is very large even though you put the same force notice the pressure becomes very small so in these cases the pressure was very small and that's why I was not able to cut through so to cut something or to punch or something you need to have high pressure not just the force but high pressured the force has to be very concentrated okay now before we proceed let's quickly look at its units what do you think will be the units of pressure can you pause the video and think about this for a while all right well force has units of Newton's an area the standard unit is meter square and so pressure is calculated in Newtons per meter square which means it tells us how many Newtons of force is acting for every meter square of area and Newton per meter square is also often called Pascal named after the French scientist but don't worry too much about the unit's right now because we will solve problems in another video so it'll be more clear over there anyways now let's see if we can use this concept to answer our original question so if we come back to the bed of nails example usually we look at that bed and say oh my god there are so many pointy nails would it hurt but the point is because there are so many nails it doesn't hurt I mean if you were to sleep on such a bed and I don't encourage that it is a little dangerous so please don't try this at home but if someone were to sleep on this bed made of so many nails then that bed has to support his or her weight so it has to push up on that person but because there are so many nails that force gets divided over all the needles and as a result the force acting on each part of that person's body would be pretty small which means the pressure over here is pretty low but imagine what would have happened if there were less nails now one might think less nails means better write less pointy services but it's actually worse because if there are nest less nails then the amount of force is the same but now that force gets concentrated who are all these fewer nails and as a result the pressure give comes becomes much higher and that could really hurt okay what about the tank can you now pause the video and think about why a chain is needed for this tank tanks are very heavy that's the clue did you get it well it's to lower the pressure on the ground let's see how if we were to zoom in close to the wheels imagine if there was no chain over here then the wheels would be directly touching the ground right so what well if the wheels are directly touching the ground look at how tiny the contact areas are and so all the weight of the tank that huge force will now be concentrated in these tiny spots just like a needle and as a result there will be a very high pressure on the ground and that pressure could actually kind of break that ground and so if there was no chain it's a good chance that the tank would actually get a little buried under the ground and will be pretty hard for it to move but if you put a chain like that then when you put a chain over here now the force is still the same okay because the weight of the tank has not changed but look at the contact area whew that increases significantly there's a huge contact area now the force gets divided and as a result the pressure gets lowered that's the whole idea now before we wind up one small detail that I missed out just a naming thing is that we said pressure is force over area right but what's important is that that force that we are applying needs to be perpendicular to the surface it has to be perpendicular to the surface only then you press against that surface and you apply pressure imagine if you had hammered the nail this way applying a force in this direction somehow let's say then what would happen it will not apply any pressure right the nail would just slide on its surface now regardless of how concentrated that force is it'll apply absolutely no pressure isn't it and so pressure only makes sense when you're applying force perpendicular to that area and Ziggler to that surface okay and your textbooks give a name to this perpendicular force I don't know why but whenever the force is perpendicular to the surface your textbooks give a name to it and it's often called thrust and so you might see sometimes in your textbook return pressure as thrust or area but don't worry too much about that thrust is nothing but the force which is perpendicular to the surface and that's pretty much it so what did we learn in this video we saw whether your force can cut something or puncture something it depends upon how concentrated it is and that's what we call pressure and because pressure is all about calculating how much the force gets divided over a given area we calculated that way we calculated as force divided by the area and a small detail is that when you are applying pressure your force must always be perpendicular to that surface just to distinguish that from any other force just to tell that that force needs to be perpendicular some textbooks will call that perpendicular force as thrust and from this we could work out its units as well and now you finally know why sleeping on your favorite pillow is so comfortable but it's so uncomfortable to sleep on a hard brick