Transcript for:
Electrostatic Forces and Everyday Forces

we encounter so many different kinds of forces in our day-to-day lives there's gravity there's the tension force friction air resistance spring Force buan forces and so on and so forth but guess what not all these forces are fundamental gravity is certainly one of the fundamental forces of nature but turns out that most other forces that we encounter in our daily life are actually a manifestation of the electromagnetic forces these are the forces responsible for all the electric and magnetic phenomena and most of the other forces that we encounter in everyday life but how how do electromagnetic forces give rise to all of these well let's get a glimpse of that in this video now there are two parts to these forces the electric part and the Magnetic part we will save the magnetic part for future videos in this in this video we'll just stick to Electric part of it and even there we'll talk about a particular kind of electric force which you call the electrostatic forces electrostatic which also called static electricity from the word itself you can see Electro means we're sticking to Electric part and static means stationary where things are not moving a lot or maybe they're moving very slowly the reason to do that is because we want to take baby steps so first we'll consider what happens when we have static conditions then we'll see what happens when they are moving and so on and so forth okay all right so when it comes to gravity we we'll keep comparing with gravity because we are familiar with gravity okay when it comes to gravity what where does the force of gravity come from what is it due to well we know that the force of gravity comes from a fundamental property of matter which we call Mass things that have mass will produce gravitational force on each other right similarly what causes electrostatic force turns out electrostatic force comes from a property of matter called you probably heard of this charge anything that has charge will put forces on other things that have charge now an immediate question that we could have is hey if that is the case and if matter has charge and because of the charge they put electrostatic forces on each other why don't we notice that why don't we notice electrostatic forces between say planets and stars and all of those things why why don't we notice that in all everyday life well first of all we do notice them in everyday life and which we will see in in this particular video but the reason why we don't notice them in a large scale is a it's a good question and we'll come back to that but anyways if you want to see electroic forces in action it's better to start looking at things inside the atom so let's do that we've probably seen the model of an atom we have the nucleus at the center which contains protons and neutrons and we all have you know kind of like an electron cloud that surrounds the nucleus where you have electrons over there now these particles will have charge protons have a positive charge neutrons are neutral they have no charge and electrons have a negative charge okay but we may be wondering how much charge do protons and electrons have to answer that question we need to know the unit of the charge just like how Mass has a unit of kilogram charge has a unit of something called the Kum named after the scientist Charles kulam who did a lot of work on this and the symbol we use is capital c now it turns out that protons and electrons have the same magnitude of this arge they have different signs but they have the same magnitude and we call that that number e and that happens to be roughly 1.62 * 10 ^ - 9 19 Kum so it's a very tiny value in terms of kums and so we would now say that the charge on the proton is this much positive so we'll just call it+ 1 E the charge on the electron is this much negative so minus - onee and the charge on the neutron well that is zero it has no charge so it's charge is just zero and now we can immediately see a big difference between mass and charge Mass there's only one kind but charge there are two kinds positives and negatives and this will now help us understand something an atom has the same number of protons and electrons so the total charge of the atoms would just be zero because charge of the proton and charge of the electron will just cancel out and so the atom itself will be neutral and so if you consider big objects which has billions and billions of atoms it's pretty much neutral because the total number of protons is pretty much the same as total number of electrons and that's the reason why most things around us are uncharged or they might have a few extra electrons or protons so they'll have a very tiny charge but mostly uncharged and that's why we don't see electrostatic forces in action most of the time that's why at Celestial scales we don't see electrostatic forces in action because they're mostly uncharged or they have very tiny charge but at the microscopic level we do see it we see protons putting forces on other protons and other electrons of the same atom of of the different atom they're all there but if you want to study this forces the next big question we should ask is what is the strength of this Force how much force would say a proton would put on say another proton or maybe on another electron how do we figure that out well for that let's assume that we have two in general let's consider two charged particles let's call these charges as q1 and Q2 you can imagine for example these are two pieces of paper and you know these pieces of paper have some extra electrons or some extra protons let's say um so they are charged so they will put an electrostatic force on each each other the question we want to try and ask answer is what is the direction of that force and what is the strength of that Force what does that depend on let's start with the direction of the force positives will push and repel other positives negatives will push and repel other negatives in other words like charges will repel on each other but unlike charges will attract each other a proton will attract an electron positives will attract negatives so the direction of the force depends upon their charge the polarity of that charge if both are positive or both are negative they will repel if one is positive the other one is negative they will attract for Simplicity let's just assume one let's just just say that both are positive then they would repel each other so this is a repulsive electrostatic force and now the big question is what is that what is the strength of this Force depend on why don't you pause the video and just think about how you think would be they would be related to um q1 and Q2 the charges and the distance between them okay since the electroic forces come from the charges we would expect that these forces must be directly related to q1 and Q2 if either of them increase we would expect the force to be to increase and how would it be related to the distance well if you put them farther away will we expect the force to become smaller if you put them very far away we would expect them to not interact with each other at all right on the other hand if we bring them closer that means if you make this smaller the distance to be smaller you would expect the force to be larger closer they are larger the force which means you would expect an inverse relationship with the distance between them now if you put it all together we'll get something called the coolum's law and it looks like this notice the kum's law is giving us something very similar to what we predicted it is directly the force between the two charges is directly related to the to the charges themselves you can see that and it is inversely related to the distance between them and more importantly you can see an inverse Square relationship where have we seen an inverse Square relationship before hey we've seen it in gravity we've seen the force of gravity the universal law of gravitation is very similar over here G which we call the universal constant its value was about this much so what is the value of K which we call the kums constant well it turns out that the value of the kums constant K is about if is about 8.99 * 10 ^ 9 units and can you work out the units yourself well we just have to isolate K on one side and if you do that let me do that very quickly we'll get f * r² / q1 Q2 so that will be f is Newtons R squ is me squared divide by q1 Q2 is Kum squar yeah I I don't have to remember them I never remember them because I can always rearrange and figure out what the units are but that's the value of K and now that you know this if you know the value of the charges and you know how far they are we can plug in and figure out the force between them okay so let's quickly compare these two well this one similarity is the inverse Square law the farther you put them the farther you go um the smaller the force gets the force dies out very quickly but what about some differences well the first difference is you can see gravity is only always attractive but the electrostatic force can be attractive or repulsive that's because we have two kinds of charges over here right but there's another thing that we can see look at the value of K it's much bigger compared to the value of G in standard units from this we can kind of guess that the kum's law is much much stronger than the force of gravity which which means if you take for example two protons and compare the force of gravity with the force the electrostatic force the kum's force you will find the kum's force to be way stronger orders of magnitude stronger than the force of gravity and so that's why at the subatomic scale we can completely ignore the force of gravity it's the electrostatic force that dominates but as we saw once we go at a much more larger Celestial scale well now the masses are so huge and the charges are so small that the force of gravity dominates I absolutely love this how the you know at different scale the different forces dominates and now we're in a position to understand that that's it that's incredible isn't it but that's not all now we're in a position to answer our original question how electromagnetic forces or electrostatic forces get manifested as some of the daily forces that we see for example tension where does tension come from well if you to zoom into a string you'll see a lot of you know atoms over there and although atoms are neutral since because they have positives and negatives inside they can push and pull on other you know electrons and protons for example the protons can push on the other protons the protons can pull on the electrons the electrons over here can push on the other electrons the electrons over here can pull on the proton so there are a lot of forces out there and you know we can model and say that you know pretty much all these forces balance out they have to because look a string is you know pretty much static so you can assume that most of the atoms are pretty much static so they are all balanced and therefore the net force on all of the atoms are pretty much zero we say they are in equilibrium now what happens when you pull on the string let's say you put a you put a mass on this you know attach a mass over here and because of gravity pulls on the string well now because of that P some of the atoms will start moving farther away from each other equilibrium gets Disturbed net force is no longer zero it turns out of the string because the equilibrium gets Disturbed the atoms go away from each other the net force will try to bring them closer back to each other and that is how tension force is generated in a string isn't that wonderful it all comes from the electrostatic forces similarly think about where does the force of friction come from well again if we were to zoom in over here we will see that you know although things look smooth at a macro scale on a microscopic scale things are not really smooth and if we zoom in even further again we will notice that the atoms of the Box can interact with the atoms of the floor via the electrostatic forces and it's these electrostatic forces which all add up and puts you know and it all adds up and gives rise to the force of friction again it is super complicated we not try to understand exactly how the force of friction comes white opposes say the force of white opposes motion for example in some cases but it all comes from the electrostatic forces and we can use the same idea the same model to explain spring forces air resistances buo and forces pretty much contact forces other contact forces that you pretty much see in your daily life and I find it absolutely fascinating that even though these models are not very accurate I mean today we have better more accurate models what we call quantum mechanical models to explain all these phenomena better but even if you ignore that even if we consider you know simpler models like we're doing over here we can just use the idea of the electrostatic forces the kums forces to try and get an intuition behind how it manifests as most of these daily forces that we encounter in life I find that absolutely beautiful