Electric Forces Hold the Pieces Together

SOURCE: http://www.aip.org/history/electron/images/thoma3.jpg

This is Dr. Patrick Particulate.

As you can see, he takes his job VERY seriously. You could say that he’s very particular about particles.

Since he’s so busy, we are going to save him some trouble and use an Instant Messenger program to talk with him. That way he can multi-task. Good thing he LOVES teaching!

Please wait…

Loading SciMaster Instant Messenger 2.1.0 program…

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Hello Dr. Particulate. This is the Science Class.

Class: Hello Dr. Particulate. This is the Science Class.

Are you there?

Class: Are you there?Dr. P: Oh yes, Dr. Particulate at your service! Now then,I believe you are inquiring as to the nature of particles, is that correct?Class: Yes sir, Dr. P! Can you help us out?

Yes sir, Dr. P! Can you help us out?

Dr. P: You bet your cathodes I can! It would be my pleasure.Dr. P: Here, let me upload a graphic that represents a particle of matter. Then I’ll tell you more about it.Dr. P: You just interrupt me if you have questions, okay?

Sounds great! Thanks! We’re all ears! (or eyes) lol

Class: Sounds great! Thanks! We’re all ears! (or eyes) lol

Active-Edit graphic uploading from user Dr. P. . .

Dr. P: Here is a picture that I will use to represent a particle. I can edit the picture while we are chatting.

Dr. P: It is important to know that basic material particles are more than what they might appear in this picture.Dr. P: They are actually made up of even smaller parts, which act differently from each other. We call one major difference “charge,” and we say that some charges are “positively charged” and some are “negatively charged.”

Dr. P: Very good observation! =) You are absolutely right—this particle SHOULD be moving. However, I have made it look like it is standing still for now. I will correct this later. Excellent!

Wait… why isn’t this one moving? The others were!

Class: Wait… why isn’t this one moving? The others were!

Thanks! We THOUGHT they should be… ;)

Class: Thanks! We THOUGHT they should be… ;)

Dr. P: Any more questions?

Nope! This is interesting!

Class: Nope! This is interesting! Dr. P: Well excellent! Alright then, back to charges.Dr. P: So we can use a + symbol for the positive charges and a – symbol for the negative charges. Does that make sense to you?

Sure does—positive is like adding something and

Class: Sure does—positive is like adding somethingand negative is like subtracting something (+ and -).

negative is like subtracting something (+ and -).

Dr. P: Good, that works. Just remember that we are not actually adding or subtracting—the particles are made from smaller pieces of matter. Some are positively charged. Some are also negatively charged.

Right…got it. Positive and negative charges.

Class: Right…got it. Positive and negative charges.Dr. P: Exactly. Here, let me add these to the graphic…Dr. P: Can you see them? Not a perfect picture, but it should give you the idea.

We see ‘em. Look good to us.

Class: We see ‘em. Look good to us.

Dr. P: Well, these particles are always in groups.Dr. P: Something about charges is that “opposites attract” and “same-sign charges repel.” Ever heard of this idea?

Class: So what exactly do these charges DO?

So what exactly do these charges DO?

Class: Kinda... So let’s see if we got this right…

Kinda… So let’s see if we got this right…

Class: If two +’s are near each other, then they willpush apart. Same with two –’s. Right?

If two +’s are near each other, then they will push apart.Same with two –’s. Right?

Springs? But…not REAL springs, right?

Class: Springs? But…not REAL springs, right?

Dr. P: That’s right! They push each other away. When you have a + and a – near each other, they pull each other together. These pushes and pulls are called Forces.Dr. P: In fact, they are Electric Forces. When these Electric Forces are applied all over the place, it’s like having imaginary springs between each particle and its neighbors.

Dr. P: Right. We just pretend they are there.

Wait, is this because of the whole “opposites attract”

Class: Wait, is this because of the whole “opposites attract” thing?!

Dr. P: Here, let me show you what I mean…Dr. P: Bringing two particles near each other has an interesting effect.

Dr. P: You’ve got it! Yes!

Dr. P: As you can see, the negative charges and the positive charges tend to move on opposite sides from each other.

thing?!

Sure. Want to be sure we didn’t miss anything.

Class: Sure. Want to be sure we didn’t miss anything. Dr. P: Do you need to see the process again?

Dr. P: No problem. Here you go.Dr. P: How was that? Satisfied? Was it clear enough?Class: We’ve got it this time. Thanks, Doc.

We’ve got it this time. Thanks, Doc.

Dr. P: Of course. My pleasure!Dr. P: So let’s look at a simpler way of studying these charges…and how electric forces act like springs.

Uhm…well, I guess we could say that each one has a

Class: Uhm…well, I guess we could say that each one has a more positive side and also a more negative side?

Dr. P: What could you say about the particles, now?

Dr. P: Wow, you got that one right off the bat! Excellent. Let me draw in some dotted lines to emphasize this.Dr. P: It’s okay, then, for us to replace these charges with signs that show the positive and negative SIDES. This will make our model a lot less cluttered.

more positive side and also a more negative side?

That definitely makes this a LOT simpler.

Class: That definitely makes this a LOT simpler.Dr. P: And that’s the purpose of modeling: to make complex things simpler. Dr. P: You probably already know that a force is a “push” or a “pull,” depending on the situation.Dr. P: Since we are working with charges, we say that the forces involved are electric forces, as I said before.Dr. P: It would be nice if we could visualize these forces.

So a longer arrow is a bigger force?

Class: So a longer arrow is a bigger force?

Dr. P: Since forces are not physical objects, we can just draw them in as arrows. The direction of the arrow tellsus the direction of the force, and the length of the arrow tells us the strength of the force.

Dr. P: Right! And these electric forces change size based on how close or far away the positive and negative charges are from each other. You’ll see what I mean.

Wait! We see it! The attraction will win out, here.

Class: Wait! We see it! The attraction will win out, here.

Dr. P: The positive charges want to push away from each other…Dr. P: The negative charges also want to push away from each other…Dr. P: But the closest charges—the positive and negative charges that are nearest to each other—both want to pull towards each other, and being closer means stronger.

Okay, that makes a lot of sense.

Class: Okay, that makes a lot of sense.

Dr. P: You’ve got it. The “net” or overall force that results is an attractive force. Dr. P: So, if it’s just these two particles near each other, they will try to move toward each other. Here, I’ll draw in the force arrows that represents this net-force.

Dr. P: This net-force acting on the particles serves to keep the particles connected.

Alright, we are getting it, now. Thanks for explaining that!

Class: Alright, we are getting it, now. Thanks for explaining that!Dr. P: Always welcome.Dr. P: And don’t worry, I know what your next question is: “But aren’t they supposed to be MOVING”??

Class: lol! Yep, you got it!

lol! Yep, you got it!

Dr. P: Well here, let me animate this a little bit. I will addin some more particles to give you a better idea.

Wow, that’s pretty cool!

Class: Wow, that’s pretty cool!

Dr. P: The more particles you have near each other, the more “neighbors” each particle has. For every neighbor, you have another attractive force.

Class: So, more particles need more arrows?

So, more particles need more arrows?

Dr. P: See how they’re seeming to fight for control over each neighbor’s attention? Imagine trillions of these particles sharing a “neighborhood.”

Sure!

Class: Sure!

Dr. P: Remember how I told you that we could imagine springs being in between each particle?

Dr. P: Well watch this. We can replace the charge-signs and the force arrows with these imaginary “springs.”Dr. P: Simpler, no?Class: Hah, definitely! Easy way to think of them.

Hah, definitely! Easy way to think of them.

It’s the small stuff that can be confusing! We’re all glad

Class: It’s the small stuff that can be confusing! We’re all glad we have the spring model to help us understand.

Dr. P: That’s what models are all about. Making things simpler to understand. They let us study the ideas behind science without actually getting bogged down with all the small stuff.

Dr. P: Well, now that you have the spring model, would it be too much of a stretch if I made the “springs” invisible?

we have the spring model to help us understand.

Nope! Everything’s the same as before.

Class: Nope! Everything’s the same as before.Dr. P: There—no springs! Has anything changed?

Dr. P: Does that make sense?Class: Sure! The springs and arrows were all just models to help explain WHY the particles do what they do.Dr. P: Well done. Now you better understand what is going on between particles that make up materials.

Sure! The springs and arrows were all just models tohelp explain WHY the particles do what they do.

Well thanks very much Dr. Particulate!

Class: Well thanks very much Dr. Particulate!

We’ve learned SO MUCH from you today!

Class: We’ve learned SO MUCH from you today!Dr. P: That’s great to hear! There’s more to learn, of course, but I’m sure that your teacher is well prepared to teach you all about particles.Class: Definitely! We’re looking forward to learning more

Definitely! We’re looking forward to learning more

Dr. P: If you need me again, just use the Instant Messenger program. I’ll be around.Dr. P: Enjoy the adventure! Goodbye =)

We will! Thanks again! Bye!

Class: We will! Thanks again! Bye!

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Closing SciMaster Instant Messenger 2.1.0 program…

Shutting Down Computer…

What next?Well that was great of Dr. Particulate to tell us all

about how electric forces govern the way particles of matter interact! Are you psyched to learn more?

Hmmm…I wonder…what’s the difference between between a SOLID, a LIQUID, and a GAS??

We will be using the spring-model again to help explain how particles interact in these different forms.