Positive and negative charges

 

Imagine we take a balloon that does not have a charge and we rub it on our head. We are now giving it a charge. So we could move it up to something neutral, like a wall and if we let it go it will just stay there. Now imagine if we take another balloon and we charge that in a similar matter. It should have the same charge as the balloon. And so if we hold it up next to it and let it go, what is going to happen? It will actually be repelled by that object. And so scientists speculated there are two types of charges. And we call those positive and negative charges.

So an electric charge can be positive or negative. If we have a neutral object it is going to have an equal amount of each of those different charges. But if it is a charged object, like a balloon, then it is going to have differences in the number of electric charges that it has. If it is a negatively charged object it is going to have more negative charges.
And if it is a positively charged object it is going to have more of the positives. Now let's say I bring two objects next to each other that have different charges. What is going to happen? There will be an attractive force between the two. But if we take two objects that have the same charge and bring them next to each other, that could be both positive or both negative, they are going to repel each other. Now, why did the balloon stick to the wall if the wall did not have a charge? We had not done anything to it? Well if you move a charge up to a neutral object what it can do is it can polarize that object. It can move some of the charges to one end. And what it does is create a similar charged object.

So an electric charge can either be positive or negative. And so if we are looking at a neutral object, how many of those charges are we are going to have in that object? An equal amount of each. Now let's say we take a charged object, a charged object like that balloon, what are we going to have? We are going to have more of a positive charge, if it is a positively charged object. Or if it is a negatively charged object we are going to have more of the negative charges inside it. Now let's say we take two neutral objects, so two balloons that we have not changed, and we move them right next to each other. What is going to happen if we let them go?
Nothing is going to happen. There is going to be no attraction between the two because the charges are equally distributed.
Let's say we take two objects and two objects that have opposite charges. So the one on the left has a negative charge, the one on the right is going to have a positive charge. If we let these go what is going to happen? There will be an attractive force between the two. Opposites attract. Let's say we take two objects that have the same charge and move them next to each other. In this case, they both have negative charges, what will happen when we let go? They are going to push away from each other. Same thing if they are both positive. If I let them go, they are going to move away from each other.

Now let's say we take a charged object, so that is the one on the left and then we have a neutral object, that is going to be the one on the right, watch carefully what happens as these two come together. So as I move the charged object towards the neutral object what it is doing is it is polarizing those charges.
It is moving the negative charges farther away. Why?
Because they are being repelled by these negative charges. The positive charges are moving towards it. And so now there is an attraction between this polarized, what used to be a neutral object.
And so PHET makes a wonderful simulation that kind of walks you through that. What we are going to do is take a balloon and we can move that balloon around. And if we let it go it just stays where it is. But let's say we want to charge it what we can do is we can rub it on a sweater. And now we are applying a charge to that balloon so when we let it go it is going to go right over to the sweater.

And so if we move it next to the wall and let it go it will stay there. But if I get it close to the sweater then it is going to be attracted. And so let's reset this whole thing and look at the charges now. So you can see that all of these objects are now neutral. They have equal amounts of charge. But as I rub it on the sweater what we are really doing is we are pulling those negative charges off the sweater. And now they are on the balloon. So now that balloon is a negatively charged object. And the sweater is a positively charged object. So if I let it go it moves right next to it. We move it next to the wall you can see it is polarizing this neutral object of the wall.

So we are not transferring charges. But if we move it next to it. It is attracted.

Let's get two balloons now and remove the wall. So let us add negative charges on this one balloon. And now let us add more negative charges on another balloon and what is going to happen?
Well as we move that balloon next to the other balloon these are like charges and so you can see that they are repelling each other. And it eventually would like to go back to that sweater. Okay. So did you learn the following, to explain a two-charge model of electric charge? Again if it is a neutral object we are going to have equal amounts of each of those two different charges. Did you learn that the distribution of those charges tells us if the object is going to be positively charged or negatively?

You can see this would be a negatively charged object here. And then finally did you learn to explain how the polarization of the electric charge or separation of that charge in a neutral object can lead to an attraction? So we have an attractive force here between the charged balloon and what used to be a neutral wall. I hope so. And hope that was helpful.