 Hey guys, I just wanted to throw another Coulomb's log sample here at you This one's a little bit different as you can see because we don't have two charged objects now We have three, but it's still a this is still a 1d example Or I sometimes call these here's a fun word to spell Co-linear I think it has one L Meaning that co they're together on linear a line so they form one nice straight line We'll look at some 2d ones a little bit later on so in this question We're asked to find the force on the second charge, which is this negative guy here in the middle We have the separation of all the charges And we also have the magnitude of the charges either positive or negative in microcoulomb's again First thing we're going to do here. Just figure out the magnitude of the forces Then we're going to worry about the direction of the forces in a minute So I'm going to call this first one here the force of object 1 on object 2 Okay, so force of 1-2 So to calculate that here comes Coulomb's law the electric force is K Q1 Q2 over our squared for K. We're putting in Coulomb's constant 8.99 times 10 to the 9 Put those units in Newton meter squared for Coulomb squared And then we're times get by the charges so we have 2 times 10 to the negative 6 Coulomb's and For the negative charge 3 Times 10 to the negative 6 Coulomb's you notice I don't put the negative sign in for the negative charge because like we said the other day This is going to give us an absolute value of the electric force So there's actually no need to put the negative sign in if you do you're going to end up getting a negative force And that's going to throw you off because this force may or may not be negative So we're going to decide that in a minute We're not going to decide it from the equation, but from the the picture and the nature of the charges I also converted from centimeters to meters. That's going to be important as well. Okay, so I'm going to find the first force Grab the old calculator here This is always interesting So 8.99 You'll also notice I'm not using times 10 to the power of I like to use the e button It's just a lot slicker I find and you're less likely to make a mistake with brackets if you're using the e button So I like to do that. Oops. We've got a negative sign and I can divide this by 0.4 squared and don't forget to square boy That's probably one of the most common mistakes with Coulomb's law. So for our force, we're getting 0.33 7 1 nudes Okay, so this is the one that I'm calling force of one on two Now if you don't mind just to save us all a little bit of time, let's talk about the force of of Three on two and I'm just going to figure that one out on my calculator I won't actually write it out if this was you doing under the test On a test you would write this out yourself But you know what we can just per second enter and the only things I need to go in here and change are It's not two micro coulombs now. It's five and the separation isn't point four. It's One point two meter squared Okay, so that's going to give us a zero point zero nine three six Zero point zero nine three six newtons. Okay step one. We just find the two forces Now the second step is probably the one kids have the most trouble with is it's actually figuring out which direction or the force is Going to act in so let's take a look at this first force I have a positive charge here on the left and I have a negative charge in the middle I want to know what the charge or what the force on the second charge is for right now Just ignore the third charge altogether think about these two. What's the direction of the force between them? Well, if I was to just hold this positive charge still the negative charge would move towards it It would be attracted to it So this force of one on two right here is going to be acting to the left Because the positive charge will attract the negative charge make it move to the left and Our usual convention is anytime you have a force going to the left We're going to call it negative, so I'm going to go and I'm going to make sure I have that force as a negative value Now let's take a look at the other one. Well same sort of situation here now If I'm looking at the force of three on two I completely ignore the first ball That one doesn't matter right now, and it's going to be an attraction force so if I hold this one still and Charge two moves. It's going to move to the right. So that's my direction of force of three on two. It's a positive. I Know sometimes kids say oh well, you know if if the negative charge here is moving towards The positive charge here then this distance will change. We don't worry about that This is all happening at the same time before any of the distances have a chance to change We're just ignoring one of them and only dealing with two of the three at any one given time To finish off if we want the total force or the net force We just have to add those two together and now that I've already called one of them negative And I've dealt with the vector nature of the forces. This is a pretty easy step. It's just adding them together So this is essentially what we're going to do in these nice code linear 1d problems where you have maybe two point charges so hopefully this was helpful and If you have any more questions about 2d problems, you can feel free to shoot me an email or You can take a look at the website. I do have some notes On 1d and 2d problems on LD industries.ca and you can kind of check them out to see How we could do this example and a few more Complicated ones as well. So our final force is going to be zero point two four three five for sick digs I just want zero point two four Newton's and it's going to act to the left Have a good day. We'll talk to you guys later