Subtitles section Play video

• Hi. It's Mr. Andersen and this is AP physics essentials double O 7. It is on positive and

• negative charges. Imagine I take a balloon that does not have a charge and I rub it on

• my head. I am now giving it a charge. So I could move it up to something neutral, like

• a wall and if I let it go it will just stay there. Now imagine if I take another balloon

• and I charge that in a similar matter. It should have the same charge as the balloon.

• And so if I 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. And 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 of the 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? I 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

• charged 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 that two objects that

• have opposite charge. So the one on the left has a negative charge, the one on the right

• is going to have a positive charge. If I 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 I 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 neutral object. And so PHET makes a wonderful simulation that kind of

• walks you through that. So what we have got here is the address down below and I will

• put a link in the video description as well. So what I am going to do is take a balloon

• and I can move that balloon around. And if I let it go it just stays where it is. But

• let's say I want to charge it what I can do is I can rub it on a sweater like this. And

• now I am applying a charge to that balloon so when I 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

• I am really doing is I am 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. Now watch what happens when

• I move it next to the wall you can see it is polarizing this neutral object of the wall.

• So I am not transferring charges. But if I move it next to it it is attracted. Let's

• get two balloons now and remove the wall. So let me add negative charges on this green

• balloon right here. And now let me add more negative charges on this yellow balloon and

• what is going to happen? Well as I 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

• charged balloon and what used to be a neutral wall. I hope so. And hope that was helpful.

Hi. It's Mr. Andersen and this is AP physics essentials double O 7. It is on positive and

Subtitles and vocabulary

Click the word to look it up Click the word to find further inforamtion about it

Positive and Negative Charge

• 80 11
Cheng-Hong Liu posted on 2015/02/23
Video vocabulary