Lesson 4. Lesson 4 - Modeling a Syringe

Umit Aslan, Umit Aslan, Royi Lachmy, Umit Aslan
Chemistry
80 to 90 min
Introductory High School Chemistry
v1

Overview

In this activity students brainstorm how compressible objects filled with air (such as air mattresses) are able to hold up the weight of a heavy object. Students then predict and observe the behavior of a plastic syringe. Using a basic syringe model in NetLogo students explore how the plunger level is related to air particle density on either side of the plunger. Students predict and explore the effects of pushing or pulling on the syringe plunger on the net forces acting on the syringe plunger. Students then design an experiment to test predictions about how particles in and outside of the syringe respond to these external forces. Finally, students using what they know about particle behavior, students explain how an inflatable air mattress can hold an individual and why the mattress returns to its original shape after the weight has been lifted. The teacher leads a consensus building discussion on particle interactions that account for these behaviors.

Standards

Computational Thinking in STEM
  • Computational Problem Solving Practices
    • Developing Modular Computational Solutions

Acknowledgement

Cite the Modelsim research

Activities

  • 1. Brainstorm
  • 2. Exploration 1 - Predict and Explore
  • 3. Exploration 1 - Procedures
  • 4. Exploration 1 - Follow Up
  • 5. Exploration 2 - Predict
  • 6. Exploration 2 - Procedure & Drawings
  • 7. Exploration 3 - Predict
  • 8. Exploration 3 - Procedure
  • 9. Exploration 3 - Predict
  • 10. Exploration 3 - Procedure
  • 11. Exploration 3 - Follow Up
  • 12. Follow Up

Student Directions and Resources


In previous activities, you had a chance to explore the particulate nature of matter. Specifically, you experimented with how gas particles diffuse throughout a room and how that behavior changes with temperature. In this activity, you will continue to experiment with gas particles and work to understand how the movement of these particles relates to pressure.

Purpose: How can objects inflated with air hold up the weight of other objects?

Overview: To investigate this question, you will record observations of a syringe filled with air, you will model the syringe together as a class, and will analyze the results from the model to explain the behavior of the syringe.

1. Brainstorm


Brainstorm around this topic by considering the following questions. Include your response in the question below. 

 


Question 1.1

Why do inflatable objects (such as an air mattress or a workout ball) change shape when you sit or lie on it?

If the object is only filled with air, how is it that it can hold your weight up?

2. Exploration 1 - Predict and Explore


Question

"Why can I compress or expand a syringe filled with air?"

Predict

You will be given a syringe filled with only air and will cover the open end of it with your finger to close it off. Once the syringe is closed you will try to push down on the plunger. With the syringe still closed you will also try to pull the plunger out.

 

 


Question 2.1

With the syringe capped at the end, do you think you will be able to push the plunger all the way down so that there is no volume left in the syringe for the air?



Question 2.2

What do you expect to feel as you push the plunger down more and more?



Question 2.3

With the syringe still capped at the end, what do you expect to feel as you pull the plunger out a bit?



Question 2.4

With the syringe still capped at the end, if you let go of a plunger that you pushed in, what do you expect will happen to it?

3. Exploration 1 - Procedures



Question 3.1
  1. Take an open syringe and set the plunger to half the volume of the syringe.
  2. Cap the end of the syringe with one finger. Push down on the syringe to as far as you can compress the air.
  3. Keeping the end of the syringe capped, release the plunger.
  4. Record your observations from these last 2 steps below. Include descriptions of what you felt on each end of the syringe and what the syringe did.


Question 3.2
  1. Again take an open syringe and set the plunger to half the volume of the syringe.
  2. Cap the end of the syringe with one finger. Pull the plunger out a bit (but do not pull it out all the way).
  3. Keeping the end of the syringe capped, release the plunger.
  4. Record your observations from these last 2 steps below. Include descriptions of what you felt on each end of the syringe and what the syringe did.

4. Exploration 1 - Follow Up


Answer the questions below based on the observations you just made with the syringe.


Question 4.1

Why does the plunger tend to return to where it started after you release the pressed in (or pulled out) plunger?



Question 4.2

Why do you think it became harder to pull the plunger out, when you expanded the air in the syringe more?



Question 4.3

Why do you think it became harder to push the plunger in, when you compressed the air in the syringe more?

5. Exploration 2 - Predict


Question

"Why does the plunger push back when I push on it?"

Model Rules

Your teacher will demonstrate a new model that represents the syringe. The blue wall will represent the edge of the plunger in the syringe. It is allowed to move back and forth within the piston depending what pushes or pulls on it. It can not move further then the edge of the syringe.


Question 5.1

How do you think the motion of the plunger wall will compare when particles are put on only the inside or only the outside of the syringe compared to when particles are put on both sides of the syringe?

6. Exploration 2 - Procedure & Drawings



Question 6.1
  1. Set the MOUSE-INTERACTION to "none - let particles move" (you can choose anything else) so that you control when the particles begin to move.
  2. Press GO/STOP/ADD ELEMENTS to run the model.
  3. Set the MOUSE-INTERACTION to “draw basic wall” or “draw red removable wall” or “draw blue removable wall”. Then add a wall to the bottom of the syringe so that its end is capped and the inside of the syringe is a closed system.
  4. Set MOUSE-INTERACTION to “add green particles”. Add particles to either the outside or the inside of the syringe (but not both) as demonstrated in the picture to the right.
  5. Set the MOUSE-INTERACTIONS chooser to “none - let particles move” to allow the particles to begin to move.
  6. Draw a sketch of the plunger level graph below.

 

Note: Draw your sketch in the sketchpad below


Question 6.2
  1. Set the MOUSE-INTERACTION chooser to anything that isn't "none - let particles move", Press SETUP, and then GO/STOP/ADD ELEMENTS to run the model again.
  2. Add particles both outside and inside of the syringe and on both sides of the plunger, so that a relatively equal density of particles is represented on both sides of the plunger.
  3. Save the state of your model for later use by clicking the "SAVE" button.
  4. Set the MOUSE-INTERACTION Switch to “none - let particles move".
  5. Sketch the plunger level graph below.

 

Note: Draw your sketch in the sketchpad below


Question 6.3

Why does the plunger move to one end of the syringe when particles are put on only one side of the plunger?



Question 6.4

Why are there some minor fluctuations in plunger position when particles are put on both sides of the plunger?



Question 6.5

Why does the plunger position remain relatively stable when particles are put on both sides of plunger?

7. Exploration 3 - Predict


We are now going to start experimenting with a modified version of the virtual syringe model that will allow you to simulate applying upward and/or downward forces by drawing a force graph.  

Watch the short video below that demonstrate how to draw an applied force vs. time graph in the model. Pay close attention to which part of the graph represents a push applied to the plunger, and which part represents a pull applied to the plunger.

Positive forces represent an external pull and negative represent an external push.

 


Question 7.1

Notice that part of this graph on the right represents no external push or pull applied to the plunger.

Predict
The plunger position will start at 0. The maximum plunger level is 15 (pulled all they way out) and the minimum is -15 (pushed all the way in). What will the shape of the graph look like over the time of model run for the force graph above? Write your answer below:



Question 7.2

Sketch your prediction for the graph of the plunger position over the time of model run for the force graph seen in the previous question.

Note: Draw your sketch in the sketchpad below


8. Exploration 3 - Procedure


Now it is your turn to experiment with the Virtual Syringe Force graph model.

  1. As you did in the previous exploration, create a world with an even number of particles both inside and outside of the syringe.
  2. Press the "Draw Force vs Time Graph" button near the bottom of the NetLogo screen.
  3. Click and drag in the graph part of the view to draw the general shape of the external force graph shown to the right.
  4. Using the "SAVE" button, save the state of your model so that you can repeat the experiment if you need to.
  5. Press PREPARE FOR EXPERIMENTAL RUN and then press RUN EXPERIMENT buttons to test the effects of the force graph on the model.
  6. You will sketch the shape of the Plunger Level graph and the shape of the Net Particle Forces graph in the following steps.

 


Question 8.1

Sketch the Plunger Level graph for the previous run.

Note: Draw your sketch in the sketchpad below


Question 8.2

Sketch the Net Particle Forces line (that appears in the "Forces on Syringe Plunger" graph) from the previous run.

Note: Draw your sketch in the sketchpad below


Question 8.3

Compare the shape of these three graphs:

  • Net Particle Forces graph
  • External Forces graph
  • Plunger level graph. 

Why does the trapped air in the bottom part of the piston tend to push back more, the further the piston is pressed down?



Question 8.4

Why does the general trend of the Net Particle Forces graph appear to be the additive inverse of the External Forces Graph?

9. Exploration 3 - Predict



Question 9.1

If you used the graph below as a script to follow for pushing and pulling on the plunger of a real syringe, describe what you would doing during first half of the graph? What would be different during the second half of the graph?

 



Question 9.2

If you ran the graph below as the external forces for the syringe model, with air on both the inside and outside of the syringe, sketch your prediction of how the plunger level of the piston would change over time to the right.

​

Note: Draw your sketch in the sketchpad below


10. Exploration 3 - Procedure


  1. Import the world you saved that has the syringe capped and different colored particles on the inside and outside of the syringe by clicking the "load another" button and selecting the file you saved earlier.
  2. Press "Reset Axes" and then "Draw Force v Time Graph" to draw the shape of the external force graph shown to the right.
  3. Press PREPARE FOR EXPERIMENTAL RUN and then press RUN EXPERIMENT to test the effects of the force graph on the model.
  4. You will sketch the shape of Plunger level graph and the shape of the Net Particle Forces in the following steps.

 

 


Question 10.1

Sketch the Plunger Level graph for the previous run.

Note: Draw your sketch in the sketchpad below


Question 10.2

Sketch the Sum of Forces line (that appears in the "Forces on Syringe Plunger" graph) from the previous run.

Note: Draw your sketch in the sketchpad below


11. Exploration 3 - Follow Up



Question 11.1

How do the actions of the particles, both inside and outside of the syringe, lead to a situation where the net force on the plunger is zero during a plunger pull?



Question 11.2

When pulling the plunger, at what point are the net forces on the plunger equal to zero?



Question 11.3

How do the actions of the particles, both inside and outside of the syringe, lead to a situation where the net force on the plunger is zero during a plunger push?



Question 11.4

When pushing the plunger, at what point are the net forces on the plunger equal to zero?



Question 11.5

What aspects (if any) of your prediction for the plunger position graph, matched the outcomes in the model?

12. Follow Up


Now that we've completed a number of explorations about how force interacts with pressure, lets revisit the questions asked at the beginning of the activity.


Question 12.1

 Why does an object filled with air return to its original shape when you release the pressure you've placed on it?



Question 12.2

An inflatable object (such as an air mattress or a workout ball) changes shape when you sit or lie on it. If it is only filled with air, why can it hold you up?