Air Pressure

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Objective

SWBAT define air pressure, identify the instrument used to measure air pressure and convert between units of air pressure | SWBAT identify the relationship between air pressure and atmospheric variables (temperature, humidity, & air pressure)

Big Idea

This lesson deals with all the various aspects of air pressure - instrumentation, factors affecting it, and how it changes as result of different atmospheric conditions

Lesson Introduction

We start off this lesson with a (literal) bang with a demonstration, but then dive right into some important relationships between air pressure and various other atmospheric variables, including temperature, altitude, humidity, and density. I feel that this is a lesson that doesn't bode well for student understanding without the conceptual framework for how air pressure actually works, something we try to explore early on in the lesson (also, see the Reflection in this section for more context). This is no doubt a tough lesson, as it's easy for students to misremember the variables in place for all the stuff happening here!

Materials Needed:

  • Hot Plate
  • Soda Can (empty!)
  • Water
  • 1000 mL beaker or container large enough to hold soda can
  • Ice (if not available, you can easily use chilled water as a substitute)
  • Tongs/Heat-Resistant Gloves

[Note: For embedded comments, checks for understanding (CFUs), and key additional information on transitions and key parts of the lesson not necessarily included in the below narrative, please go to the comments in the following document: 5.6 - Air Pressure (Whole Lesson w/comments). Additionally, if you would like all of the resources together in a PDF document, that can be accessed as a complete resource here: 5.6 - Air Pressure (Whole Lesson)[PDF]. Finally, students may need their Earth Science Reference Tables [ESRT] for parts of the lesson (a document used widely in the New York State Earth Science Regents course) as well.]

Do Now & Objective(s)

10 minutes

Students come in silently and complete the (attached) Do Now. In this case, the Do Now is a review of material from earlier in the unit, especially what recent assessment data has shown they need a bit of extra support in. After time expires (anywhere from 2-4 minutes depending on the type of Do Now and number of questions), we collectively go over the responses (usually involving a series of cold calls and/or volunteers), before I call on a student and ask them to read the objective out loud to start the lesson.

As a general note, the Do Now serves a few purposes:

  1. It serves as a general review of the previous day's material; (again, this is a bit different, as they are reviewing for the quarterly Interim Assessment)
  2. It is a re-activation of student knowledge to get them back into "student mode" and get them thinking about science after transitioning from another content area or alternate class;
  3. as a strategy for reviewing material students have struggled with (for example, using this as a focused review for material that they have struggled with on unit assessments or recent quizzes); and,
  4. It is an efficient and established routine for entering the classroom that is repeated each day with fidelity (I never let students enter the classroom talking. While it may seem potentially severe to have students enter silently each day, this is both a school wide expectation and a key component of my classroom. In many respects, I find that students readily enjoy the focus that starting with a quiet classrooms brings each day).

Demo & Text

25 minutes

After the Do Now, the next section involves a brief demo, which can be alluded to on the first page of the Demo & Text resource. Specifically, this involves crushing a can of soda using ice/cold water, a container, a hot plate, and and some tongs to move the hot soda can into the ice bath. I wish I recorded the experiment, but the same concept is illustrated in the Youtube video below:

Once we do the experiment (which the students love), we try to break down exactly what happened for a few minutes. Specifically, the water vapor had a lower pressure than the air did, so when the can was inverted, the water vapor that had displaced the air inside the can was at a lower pressure than the surrounding water pressure, causing the can to collapse. 

After this, and to help explain that we are at the bottom of an "ocean of air" in the atmosphere, I have students transition to the next page in the Demo & Text resource, where we explore the variables a bit more. 

We go through this information together because I periodically want to stop and really drive some points home. As noted in the lesson Introduction, I think it's important to develop a really strong conceptual understanding of what's happening here. When students are forced to memorize variables absent the proper context of exactly what's happening, I think it's a missed opportunity for some real, deep learning...and the students are much more likely to forget or mix up the variables if they fail to understand why the relationships are inverse (or direct). 

So we read together as a class, with me periodically stopping or asking students to answer the embedded comprehension/CFU questions as we proceed. Once we finish all the variables, I like to to do a "pop quiz" round of quick, rapid-fire CFUs to help students internalize the relationships between air pressure and density, temperature, humidity, and altitude. They're fairly simple, but they basically consist of recall questions based on what we just covered (i.e. "Joe, what's the relationship between altitude and air pressure? Why?"). I let them "phone a friend" if they're stuck, but even if they do, I at least make them repeat the correct answer before we move on. We do this for just a few rounds before jumping into the practice section below. 

Practice

20 minutes

The Practice section in this lesson is, like the vast majority of questions found in all of my classwork and homework, is 100% Regents-based. All of the questions come from prior Regents examinations. Likewise, as I try to generally do with all of my lessons, the questions are mostly organized to get increasingly more difficult and increase in complexity, which is why the harder questions tend to come toward the end. This is one of the harder lessons in the unit in terms of relationships and content acquisition - students tend to mix up or misidentify the relationships here, especially in relationship to temperature/humidity, etc. The best way I've found to combat this is to give them the chance to identify and correct their mistakes in questions of this type, which is why this section is a little extended as per my usual lessons. 

As I mention above in the lesson Reflection (see Introduction), I think it's important for students to develop a deeper conceptual understanding, which should have been done in the earlier section. This section is meant to reinforce that knowledge they've already learned. In essence, in building the conceptual framework, they're now cementing it into their long-term memory with dedicated and focused practice. To help facilitate this, I think it's important during practice to help students, especially those strugglers, really think about the notion of relationships in a conceptual way - don't have them memorize it, but have them draw it out if they're struggling. For example, in thinking about the temperature/air pressure relationship, it helps to see it illustrated at a molecular level. As the air is heated, the molecules move faster and start bumping into each other more, which spreads them apart. Since they're more spread out, there are less air molecules "weighing down on you," which makes air pressure drop. 

In terms of student work habits, I tend to sometimes make this decision in the moment, and as a response of what I know about the students and how they're processing the material on, but I'll either ask them to work independently, in partners, or (sometimes) give them the option. Usually, before starting practice, we tend to go over some steps for self-help ("What should you do if you're stuck?"), and I might reference a previously used multiple-choice or free response strategy in order to build their skills while simultaneously learning content (as an example - one popular one we always use - "If you aren't sure what the right answer is, see if you can eliminate some wrong answer choices"). I tend to circulate for compliance and then hone in on specific students while they're doing this. 

After about 10 minutes, we go over their responses. Students who finish early are encouraged to work on the exit ticket (resource below) and double-check their responses. We use a combination of strategies (active voting, cold calling, popsicle sticks, volunteers) to go over the responses, where students correct their work and ask any clarifying questions. 

Exit Ticket & Closing

5 minutes

In the last few minutes of class, I have students complete the daily Exit Ticket. For the sake of time, I have students grade them communally, with a key emphasis on particular questions and items that hit on the key ideas of the lesson (Note: This usually manifests as students self-grading, or having students do a "trade and grade" with their table partners). After students grade their exit tickets, they usually pass them in (so that I can analyze them) and track their exit ticket scores on a unit Exit Ticket Tracker. 

After students take a few seconds to track their scores, we usually wrap up in a similar way. I give students time to pack up their belongings, and I end the class at the objective, which is posted on the whiteboard, and ask students two questions:

  1. Do you feel that you mastered the objective for the day?
  2. Can you reiterate one thing you learned about (in this case, information on where the vertical ray falls on the respective Equinoxes/Solstices, etc.)?

Once I take 2-3 individual responses (sometimes I'll ask for a binary "thumbs up/thumbs down" or something similar), I have students leave once the bell rings.