Using Visual Examples to Teach Boyle's Law
Lesson Objective: Make sense of Boyle's law with demonstrations and concrete models
Grades 9-12 / Science / Chemistry

Thought starters

  1. How does the use of marshmallows and shaving cream make the concept more concrete for students?
  2. How do the atoms on sticks help students develop a mental model of particle movement?
  3. Note how Mr. Groves connects the visual and concrete models back to the equation.?
12 Comments
An excellent way of making students understand a rather difficult Boyle's Law concept. I admire the student involvement especially in the demonstration of atomic vibrations in solids and gases and the teacher's imitation of a particle bumping against the wall. Well done!
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Great lesson, thanks for sharing this. I was particularly impressed by the student involvement and understanding as a result of this approach.
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This lesson has other applications when we talk to students about the phases of matter. Using the demonstration of atomic vibrations will help students visualize these "unseen movements" in a different way. Thanks for sharing the lesson.
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Thanks for sharing!!!! I was very impressed with the way that you made real life applications. You are a great presenter!!!
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Awesome..An excellent sharing that I can use in teaching Boyles Law..Thank you Mr. Groves!
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Transcripts

  • 01:00:00 Chemistry written on notebook paper
    Shaving cream experiment [MUSIC]
    Molecule models
    Atom models on sticks
    Paul and students
    Test tubes PAUL

    01:00:00 Chemistry written on notebook paper
    Shaving cream experiment [MUSIC]
    Molecule models
    Atom models on sticks
    Paul and students
    Test tubes PAUL GROVES (VO):
    Anytime you can make a reference back to the real world or the real student world, then that helps kind of hook the students into making sense of stuff you've seen, but if you know, what happened in that test tube is not part of...
    PAUL GROVES
    Chemistry Teacher
    South Pasadena High
    Paul (INTV) PAUL GROVES:
    ...their normal, everyday experience...
    Students PAUL GROVES:
    ...and it just stays in the classroom.
    TOUGH
    TO TEACH [MUSIC]
    Boyle's Law [MUSIC]
    EXT. South Pasadena High School
    P1•V1=P2•V2
    Boyle's Law PAUL GROVES (VO):
    Today's lesson's about Boyle's Law. Now the equation for Boyle's Law is P1•V1=P2•V2. We're trying to get into why does Boyle's Law work?
    Paul (INTV) PAUL GROVES:
    You know, we know that there's a relationship between the pressure and the volume and that they're inversely related, but why, when you decrease the volume, does the pressure get higher?
    Students PAUL GROVES (OS):
    What's the relationship between the two variables? In this case, pressure and volume?
    Pressure-Volume Laws
    P and V are inversely related
    PV=C
    The product of pressure
    and volume is constant PAUL GROVES (VO):
    Yeah, inversely related. Okay, so it wha-, as the pressure goes up, what happens to the volume?
    STUDENTS (OS):
    The volume goes down.
    Paul and students PAUL GROVES:
    It goes down. And as the pressure goes down...
    Students STUDENTS:
    The volume goes up.
    PAUL GROVES (OS):
    The volume goes up.
    Paul teaching class PAUL GROVES:
    Okay? And what we were able to do with this was find out that if we take the pressure and the volume and multiply...
    Students PAUL GROVES (OS):
    ...together, they come out? It's a C word.
    STUDENTS:
    Constant.
    01:01:04 Paul teaching class PAUL GROVES:
    Constant. Okay, it came out at constant.
    Female student PAUL GROVES (OS):
    The guy who really studied...
    Paul teaching class PAUL GROVES:
    This was named Robert Boyle and he came up with this Boyle's Law...
    Robert Boyle Studied the Pressure and
    Volume of Gases
    P1•V1=P2•V2
    Boyle's Law PAUL GROVES (VO):
    ...and we actually have this formula, P1•V1=P2•V2. We did problems with it and that was not a big problem.
    PAUL GROVES (VO):
    I think that...
    Paul (INTV) PAUL GROVES:
    This is a tough concept to teach because students just don’t have that mental model of what particles are doing, because...
    Students
    PAUL GROVES (VO):
    ...everything we're doing is, is invisible. It's a very abstract sort of a concept.
    Paul teaching class
    PAUL GROVES:
    So what I have here is called a bell jar, 'cause it looks like a big bell...
    Students
    Vacuum pump
    Students PAUL GROVES (OS):
    ...and I have my vacuum pump. Okay, so what I'm gonna do is to take some marshmallows...
    Paul PAUL GROVES:
    ...and put them in a cup.
    01:01:41 Marshmallows
    Students
    Paul PAUL GROVES (VO):
    So the marshmallows are a really good food to use, so inside the sugar, there are tiny little bubbles, so each little bubble is...
    Paul (INTV) PAUL GROVES:
    ...a-a trapped gas and inside the bubbles, there are...
    Pressure
    Outside Air Pocket
    =
    Pressure
    Inside Air Pocket
    Of Marshmallow
    Vacuum pump knob
    PAUL GROVES (VO):
    ...particles that are bouncing around, and on the outside, there are particles bouncing around, so if you look at a normal marshmallow, it doesn’t change shape because they have the same number of particles bouncing around on the inside as you have on the outside and in normal conditions, those two are equal, but we change that by taking away the outside pressure with the vacuum pump.
    Marshmallows expanding in cup MALE (OS):
    Whoa. Uh-uh.
    FEMALE (OS):
    What?
    Students PAUL GROVES (OS):
    Okay, any observations?
    MALE:
    Yeah, it's... [OVERLAP]
    FEMALE:
    It's expanding. [OVERLAP]
    Marshmallows expanding under pressure PAUL GROVES (VO):
    Then I think we just go step back and um, just relate this, you know, very clearly that we saw experimentally that when the...
    01:02:23 Pressure Decreases
    Outside Air Pocket
    =
    Volume
    Inside air Pocket
    increases PAUL GROVES (VO):
    ...volume decreases, the pressure increases. We were able to take that mathematically and get a-a-a equation out of this...
    P1•V1
    =
    P2•V2 PAUL GROVES (VO):
    ...the Boyle's Law, where the pressure times the volume in one situation equals the pressure times the volume in another situation, and if the...
    Marshmallows expanding in cup PAUL GROVES (VO):
    ...pressure goes up, the volume goes down.
    FEMALE (OS):
    Whoa.
    MALE (OS):
    It happens.
    STUDENTS:
    (LIGHT CHATTER)
    01:02:47 Marshmallows compressing in cup PAUL GROVES:
    Okay, so why did that happen? Or what happened? They compressed?
    MALE:
    They looked dried up.
    Paul holding marshmallow cup PAUL GROVES:
    Yeah, they do look kind of dried up. And what makes them look dried up?
    Students FEMALE:
    [OVERLAP] 'Cause the air in the spaces between them is gone.
    Paul PAUL GROVES:
    Yeah, so inside, so like a marshmallow, if you could see really close up, what is it, like what does a marshmallow look like?
    Students FEMALE:
    Little bubbles.
    PAUL GROVES (OS):
    Yeah, so a ton of little bubbles. Okay.
    Paul PAUL GROVES:
    If we're taking the air out from the outside of them, what happens to the size of those bubbles?
    Students STUDENTS:
    They shrink.
    PAUL GROVES (OS):
    Okay, well first thing...
    Paul STUDENTS (OS):
    They expand.
    PAUL GROVES:
    They expand. Okay, then why do you think they started to shrink after that?
    Students FEMALE:
    They popped.
    PAUL GROVES (OS):
    Yeah, they popped. So we got them you know, bigger and bigger and bigger.
    Paul PAUL GROVES:
    Then they started to pop, and then they got smaller and smaller. Okay? Okay, I'll try it a little different way. They're gonna have some...
    01:03:33 Paul holding shaving cream can STUDENTS:
    Shaving cream.
    Students
    Paul covering cup of shaving cream with glass container
    Paul PAUL GROVES:
    I'm surprised you guys know what this is. Close that up. So what do we predict?
    Students STUDENTS:
    It's going to expand. [OVERLAP]
    PAUL GROVES (OS):
    And again?
    Paul teaching students MALE:
    Clean shave.
    PAUL GROVES:
    Clean shave.
    STUDENTS:
    (LAUGH)
    Shaving cream in cup
    Students MALE:
    Uh-oh. What?
    Shaving cream expanding PAUL GROVES:
    Okay, what's happening now?
    Students FEMALE:
    The bubbles are popping. [OVERLAP]
    Shaving cream PAUL GROVES:
    Yeah, do you think they'll be popping again?
    Shaving cream compressing
    Students PAUL GROVES (VO):
    So instead of saying, you know, P1•V1=P2•V2,, we can look at kind of a macroscopic level, so if we see shaving cream getting larger, you know...
    01:04:12 Paul (INTV) PAUL GROVES:
    ...that is something that you can see, but what's really going on inside?
    Paul teaching class
    Students
    Paul handing out sticks of atom models
    Female student PAUL GROVES (VO):
    So the idea here was you know, if students could kind of have a real feeling for what the particles are doing... What I was thinking, well, this could get the ah, atoms on a stick. So I took little Styrofoam balls, stuck them on the end of sticks, and students can really focus in on these...
    Paul (INTV) PAUL GROVES:
    ...ideas of the particles floating around.
    Students holding sticks with atom models PAUL GROVES:
    And what I'm gonna do is I'm gonna hold my atom right here. I need you to touch my atom. Okay, now, they're all put together like this. Would you call this a solid, a liquid or a gas?
    Students, Paul STUDENTS:
    Solid. [OVERLAP]
    Paul and atom models PAUL GROVES:
    Okay, like a solid. Okay. Is this a great model of a solid?
    Students and Paul with sticks STUDENTS:
    No.
    Atom models on sticks PAUL GROVES (OS):
    No. What do you think's wrong with it?
    Paul teaching class PAUL GROVES:
    Should there be a little motion like this to a solid?
    01:04:51 Atom models on sticks STUDENTS:
    Yes.
    PAUL GROVES (OS):
    Yeah, okay, because you know, particles, even though they're solid...
    Paul and students PAUL GROVES:
    ...they're not really moving past each other very much...
    Atom models on sticks PAUL GROVES (OS):
    ...but they are vibrating a little bit.
    PAUL GROVES (VO):
    Once they become part of the lesson and they're actually...
    Paul (INTV) PAUL GROVES:
    ...building up their own mental model of what's going on by waving the sticks around, I think that that makes it much more accessible for each person.
    Atom models on sticks
    Students and Paul with atom sticks
    Sticks hitting each other PAUL GROVES:
    So go ahead and turn it into a gas. So for a gas, okay, there's a lot more room between the particles. This is what a gas is kinda like, but what I'm more interested in is, is what is gas pressure all about?
    01:05:20 Paul (INTV) PAUL GROVES:
    That's where students have a hard time. They can tell me, you know, okay, if I decrease the volume, what's gonna happen to the pressure? They can say oh yeah, the pressure's gonna increase. And even if I put quantitatively and I say okay, let's, let's push it down to half the volume, they'll say that the pressure doubles, but then if I say why? Then they are really at a loss all of a sudden.
    Paul and students
    Atom sticks hitting paper in Paul's hand PAUL GROVES:
    So I were the wall of the container, what would happen if I were right here? Yeah, so there'd be collisions every once in a while. Okay, bouncing into the wall of the container. So what is pressure?
    Atom sticks FEMALE (OS):
    The atoms hitting the wall?
    Paul and students with atom sticks PAUL GROVES:
    Yeah, the collisions against the wall. So collisions against each other, okay, that's probably just gonna be more like heat and things, but that's not really causing pressure. Okay, you really need them bumping into the wall of the container to actually cause pressure. Make sense?
    MALE:
    Yeah.
    Atom sticks STUDENTS:
    Yeah.
    Paul and atom sticks PAUL GROVES:
    So if we brought the walls even closer, then we'd expect there to be more...
    Students and Paul STUDENTS:
    Collisions.
    PAUL GROVES:
    Collisions against the walls of the container.
    01:06:13 Students and Paul PAUL GROVES (VO):
    The part that I think that really made a difference was when it's colliding into the walls of the container...
    Paul (INTV) PAUL GROVES:
    ...because there's all kinds of collisions going on and if two particles bump into each other, that's not pressure. It's when they finally bump into the wall of the container that we're really talking about pressure.
    Paul and students holding atom sticks
    Paul illustrating what atoms do under pressure PAUL GROVES:
    If I were a particle, well, let's say we had the wall of the container right here, and then over here, we had the wall of the container right here, and if I'm the particle, then if I'm bouncing along, then I come over and bump into the wall. Okay, and I go over here and I gotta bump into the wall, and I go over here and bump into the wall, bump into the wall...
    STUDENTS:
    (LAUGH)
    PAUL GROVES:
    Bump into the wall. Okay, so the particle is gonna cause pressure every time that it collides into the walls of the container.
    PAUL GROVES (VO):
    I really do visualize all these little particles bouncing around and everything, so...
    01:06:56 Paul (INTV) PAUL GROVES:
    ...ah, if I can get them to see the same kind of thing that I see, then I know that they'll understand the chemistry the same way I do.
    Paul teaching students [MUSIC]
    PAUL GROVES (VO):
    My advice for other teachers is go back and reflect on...
    Paul (INTV) PAUL GROVES:
    ...why do I understand this? Why does this make sense to me? If that, if that makes a difference, then...
    Students holding atom sticks
    Students
    Marshmallows compressing in cup
    Paul PAUL GROVES (VO):
    ...we should be able to show that. What I hope the students will go away with on this lesson is, you know, things that they've always seen and now they look at them go oh, you know...
    Paul (INTV) PAUL GROVES:
    ...now I understand. Those are little atoms that are bouncing around. You just see that in their eyes all of a sudden. Oh, I get it. Okay, this is good.
    Students
    Paul holding marshmallows in cup
    Atom sticks
    Students
    Paul and students [MUSIC]
    Fade to black
    [CREDITS]
    [WINGSPAN PICTURES LOGO]
    01:07:44 Fade to black

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South Pasadena Senior High School
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