 Hello friends and welcome to another session on physics and continuing with our trend. We are going to discuss another important topic and that's units of force. So like you have measured mass, you have measured distance, you have measured time. So every time you measure one particular physical quantity, you must have a unit for it. For example, when you measure the length of a room or length of the floor, length of a tile, length of a notebook, length of cloth, you must have meters, centimeters, inches, length of distance. You know, the path on which you are traveling or distance between two cities you measure in kilometers or miles, likewise, we have units of force. So how much and how do we measure or how do we put a unit for a value of force? So let's discuss that. So what is SI unit of force? So you know that all the physical quantities are measured in something called SI unit. So international standard of units, we have where all the nations have accepted or agreed upon common units so that there is no confusion while they are interacting with each other or let's say when we are doing any trade or manufacturing or such transactions between two nations, then we must not rather have any confusion on how the particular quantity is measured. So we have something called SI unit of force, isn't it? So all of you are aware that SI unit of length is meters, mass is kilogram, time is second. So hence now, what's SI unit of force? So let's talk about SI unit of force. So SI unit of force is Newton. So you can notice that there is a small n E W T O N and there's a reason why it's written small and all of us know who Newton was and it is abbreviated as capital N. So whenever we have to write, let's say 20 Newton force, then we have to write 20, 20 Newton force will be written as 2 0 and then capital N. And whenever we have to write 20 Newton, Newton full, so we have to write 20 N E W 2 E O N. This is the way you should be writing. So if it is abbreviated from capital N, so capital N, and if it is in full, you want to write full unit in the full name of the unit, then the N here should be small. That's the protocol or that's the standard convention which we follow for all units and units named after scientists. So to differentiate between when we are talking about the scientist, we will write N capital, but when we are talking about the unit, then N has to be small. I hope you understood that next. So it is named in honor of Sir Isaac Newton. All of us know Sir Isaac Newton, he gave the laws of motion and multiple other contributions in the field of mathematics or physics. Now let us define one Newton. So in physics, we need to define that quantity. So how do we know what one Newton is? So how do we define one Newton? Now one Newton is defined as the amount of force. So let me go with the highlighter here so that you guys can understand. So amount of force which when applied on an object of mass 1 kg. So let's say if you have a 1 kg object, the mass is 1 kg, not the weight, please understand. So weight is 1 kg. So weight anyway is not measured in kg you will know. So hence if there is 1 kg mass and if you are applying a force of, let's say you are applying some force, you don't know what this amount is and you observe that this body starts moving with an acceleration. It starts accelerating and the value of the acceleration is 1 meter per second square. So if that is happening, if this is the thing which is happening, then we say that the amount of force which you are applying onto this body is nothing but 1 Newton. So once again, so there is a 1 kg mass, you are applying some force. That force which produces an acceleration of 1 meter per second square on the body is called 1 Newton force, right? So hence that's how we define 1 Newton force, perfect. Let's go to our next information, okay? So you can see here while writing in full, it's written as 1 Newton and while you are writing in small, then you have to write simply capital N, is it okay? Is it okay now? So other units of force, let's also now describe other units of force. Is the Newton only 1 unit or are there some other units? What are the units which we were using previous to Newton? So what are those information? Let's go through them one by one. So in 1946, there was a conference in France. So this is called CGPM, they standardized the unit of force in the MKS system of unit. So prior to SI units guys, there was something called MKS system which was used in United Kingdom and that MKS system was nothing but very similar to what today we have as SI units. So mass was measured in kgs, time was measured in second and length was measured in meters. So meter kg second system, abbreviated as MKS system of units. Now in 1946, this was the conference which took place and they defined what will be the definition of 1 Newton force and here is where the definition of 1 Newton came and that is the amount needed to accelerate 1 kilogram of mass at the rate of 1 meter per second squared. That's what we learned in the previous slide. So this is nothing but definition and in 1948, the 9th CGPM, so again there was a conference and this was 9th in number from the beginning. So in 9th CGM, they adopted the name Newton. So they gave this definition and name and they said 1 Newton will be equal to 1 meter, 1 kg meter per second square. So let me write it as 1 kg meter per second square. So this is how Newton was defined. So if 1 kg mass is accelerated by acceleration of 1 meter per second square, that amount of force will be called as 1 Newton. So that was adopted in the year 1948, so it's like almost 70 plus years where we are using Newton as the unit of force. There were some other units which were used or which were in vogue. Let's understand what were those units. You can see these were the units. So dyne was 1 and it is nothing but the conversion factor you can see 1 dyne is 10 micro Newton. So typically we say 1 dyne is equal to 10 to the power minus 5 Newton or 10 micro Newton whichever way. Both are same. There was grain force, there was gram force, there was spondyl, there was ounce force, pound force and kilogram force, kgf or kgf is still used in many application areas. So 1 kgf is nothing but the amount of force the earth applies on a 1 kg object and that is nothing but 9.80665 Newton, something like that. So these were some common units which were in vogue, which were used before we adopted Newton as the SI unit, is it? Now let us also look at the values of this thing. So how much is 1 Newton for? So if I talk about measuring 1 Newton, where do you see 1 Newton across or around yourself? So let us talk about that. In general terms anything that has a mass of 102 grams, so if you take 102 grams of sugar, 102 grams of milk, 102 grams of sand and put over your palm then the amount of force which the earth is applying on that body or that particular substance which is applying a force or the amount of force with which the earth is attracting the body will be 1 Newton force. So what I am saying, measure 102 grams of anything. So 102 grams of anything is now being pulled by earth. So the amount of force with the earth is applying on 102 grams of anything is called 1 Newton force. So it is typically 1 Newton force. So what are such objects, let us have a look at those objects which apply 1 Newton force or which is being attracted by earth by 1 Newton force. These are a few objects. You can see there is oranges, some pieces of oranges are there, some milk powder or something is there and then there is milk. So you can see this much milk, 3.5 ounces of milk you can see here. Typically weighs 1 Newton force and there are 2 carrots around 101 grams is there. These are some gold biscuits which are around 102 grams. So this is 1 Newton force and some cereals are there. So you can see all of them are applying or all of them are being pulled by earth by 1 Newton force. It will be also good to just have a look on the magnitude of force. So what are typical values of forces around us? So let us have a look. So you can see force of gravity between proton and an electron in hydrogen atom is how much? 3.6 into 10 to the power minus 47 Newton. It is too small a number. Now weight of an electron, the amount of force by which the earth is attracting electron towards itself will be around 8.9 into 10 to the power minus 30 Newton. You can see how small that number is. So how what will be the weight of an electron almost negligible. Weight of an hydrogen atom is this much 1.6 into 10 to the power minus 26 Newton. Force of an E. coli bacterium. So you know this will be the force applied on a bacterium by your 10 to the power minus 14 Newton. Average force of human bite. So when you bite something while eating then the force your jaws are applying is how much? 720 Newton. You can you can see the 720 Newton of force is being applied. When you are on a you know train and there's a diesel locomotive which is pulling the train then the amount of force is 890 kilo Newton. So this is nothing but 890 into 1000 Newton. This much force is being applied by the locomotive on the wagons. Now you might have seen space shuttle you know leaving earth going to international space station and then coming back. So the shuttle engine main engine thrust is around this much. We are talking now in terms of mega Newton. So 1.8 into 10 to the power 6 Newton is the amount of thrust or the force. Thrust is nothing but a type of force which the engine is applying to push the rocket or to push the aircraft upwards. Force of gravity between earth and moon. So the moon goes around the earth you all know. So hence earth is pulling the moon by this much amount of force 10 to the power 20 Newton. The order is 10 to the power 20 Newton. Now similarly if you if you try to measure the force of gravity between earth and sun the order is of 10 to the power 22. So you can see right from 10 to the power minus 47 to 10 to the power 22. So a wide range of forces which are there in nature. So this just gives you an idea of what typically your Newton is one Newton is one Newton forces and what are the typical values of forces being applied by multiple objects around us. So that will give you a sense of the magnitude of the force around in nature. So this way we learned about the units of force. Now we know that units are very very important units are the soul of physical quantities. So you will have to apply that Newton unit wherever required and hence while all science communication we need to mention the units wherever we are expressing or trying to communicate about forces. I hope you understood this topic. Let's go to the next one in the next session. Thank you.