hello everyone welcome to the start of electrostatics so if we think about an atom we know that a typical atom has a nucleus and in that nucleus we have protons which are positive we have neutrons which are neutral so i'm just going to i'm not going to put anything there so i'm going to put some p's over here and some ends there's one n then on the outside we've got electrons if or what i first want to say is that pro electrons are negative so if we look at this molecule as a if we look at this atom as a whole it's got two electrons and it's got two protons which are positive so the overall charge of this molecule is zero and so if you had to put a another atom of the same type then there wouldn't really be any force between these two because they are both neutral but if i do the following in this atom now i now have four electrons and i've got two protons so i've got a total charge which will be two minus four because the four electrons are negative and so that gives me minus two for this one on the right the charge will be two protons minus the one electron and so i've got a charge of one so now because we have a ch because we actually have a charge on both of these that isn't zero there's some type of force that will be exerted between these two they will either attract each other or they will push each other away we all know that opposites attract and so because the one charge is minus two and the other one is one they will attract each other so we have a formula that allows us to calculate that force that formula is the following it says that the force between two charges is equal to k which is a constant that will be given to you on your periodic table it has a value of nine times ten to the ninth not your periodic table on your formula sheet q1 is the charge of one of them so for example the two and then q2 is the charge of the other one so it's the one notice that i didn't say -2 that is very important don't include the signs so if one of them is negative don't put that in this calculation that's important then r is going to be the distance between the two charges now let's talk about the units q 1 and q 2 must be in coulomb that is the standard unit for charge r must be in meters so let's try an example here we have two charges and let's just give them a distance of three meters so the formula which is obviously always going to be given to you is f equals to k q 1 q 2 over r squared k is 9 times 10 to the nine it's a constant on your formula sheet q1 it doesn't matter which one we choose let's just take that one it's three coulombs this one is minus two but we do not put the minus two over there the distance between them is three and then many students forget the to the power of two and that's going to give you a six with nine zeros now what are the units well it's just a force and so that's just going to be newton's now what would these two do to each other would they attract or repulse well because they are opposite charges they would attract and so you would say attract you're not going to say left or right because this one is obviously going to move right and this one is going to move left so it wouldn't be correct to say left or right now something that confuses a lot of students is they not always going to give you the standard unit of coulombs there are four other types that they can use and they typically do use these they could use millicoulomb micro coulomb nano coulomb and pico coulomb and you need to know how to convert each of those back to coulomb so if they give you micro coulomb then you have to multiply that with 10 to the minus 3 and that will give you the coulombs that you want if they give you micro coulomb then you times it by 10 to the minus six and guys please just learn this i've got so many students who keep forgetting these it's because they're not learning it go home or sit at home and just spend 15 minutes drilling this into your head you will remember it i promise you don't always keep forgetting it it's going to make you very anxious in the test there we go and then pico coulomb is that over there the most popular ones would be these two with this one being the most popular so go ahead go learn those it follows a pattern 3 6 9 12 and you just need to somehow remember this for yourself and so that's an introduction to electrostatics thank you for watching