Category Archives: lab activities

Fluids Paradigm Lab

I taught a one-semester Advanced Physics class that cumulated in the AP Physics B exam my first five years of teaching. For the past two years, I taught an official AP Physics B course. Both of these courses were packed with content. Despite being a proponent of Modeling Instruction and incorporating it into other courses, I never felt I could make it fit in these courses.

This year, I’m teaching the new AP Physics 2 course. The focus on inquiry, deep understanding of physcs, and science practices (and less content) aligns wonderfully with Modeling Instruction.

We just started the first major unit, fluids. I guided my students through a paradigm lab to model the pressure vs. depth in a fluid. We started by watching this video of a can being crushed as it descends in a lake. I was worried students would find the phenomenon demonstrate too simple, but that definitely wasn’t the case. Like any paradigm lab, we started by making observations:

  • the can gets crushed
  • the can gets crushed more as it gets deeper
  • the top of the can appears to be sealed
  • the can must be empty (student commented that if full, it wouldn’t be crushed)

Students then enumerated variables that may be related to the crushing of the can:

  • water pressure
  • volume of water above the can
  • strength of can
  • air pressure inside of can
  • gravitational field strength (student said “gravity” and I went on a tangent about fields…)
  • temperature of water
  • atmospheric pressure
  • type (density) of fluid
  • water depth
  • speed of decent
  • dimensions, surface area, shape of can
  • motion of water

Students readily agreed that it was the water pressure that crushed the can and it is the dependent variable. In hindsight, I could have better focused the discussion by directing students to focus on the water pressure rather than the can itself. They had a lot of good ideas about what properties of the can would affect it being crushed, which I didn’t expect. I had to admit that I didn’t have any cans and we would have to focus on the fluid instead…. I was amazed that no one in my first class proposed that the depth of the fluid would play a role. Everyone in that class phrased it as the volume of the fluid in the container above the can was a variable to measure. This was fascinating to me and led to a surprising result for the students as the experiment was conducted. I think this illustrates the power of the modeling cycle and guided inquiry labs.

We next determined which of the above variables we could control (independent variables) and measure in the lab given the resources available at the moment:

  • volume of water above the can
  • type (density) of fluid
  • water depth
  • speed of decent

The materials we planned on using were Vernier LabQuest 2 interfaces, pressure sensors with glass tube attachments, three different sized beakers (for the volume variable), graduated cylinders, fluids (water, canola oil, saturated salt water).

We then defined the purpose of our experiment:

To graphically and mathematically model the relationship between (TGAMMTRB) pressure, volume of fluid above, depth below surface of fluid, decent rate, and type of fluid (density).

We divided these various experiments among the lab groups, and groups started designing their particular experiment.

At the start of class the next day, groups shared their results. I was particularly impressed with the groups investigating pressure vs. volume of fluid above a point. While they measured a relationship between pressure and volume, their experimental design was sufficiently robust that they also noticed that the same volume above the measurement point resulted in different pressures in different beakers! That is, the pressure with 400 mL of water above the sensor in the 600 mL beaker is different than in the 1000 mL beaker and different again from that in the 2000 mL beaker. After further investigation they concluded that the relationship was based on depth, not volume.

The groups investigating pressure vs. depth in fluid were confident that the pressure at a point depended on the depth below the surface of the fluid, and they had sufficient data that they were also confident that there was a linear relationship between pressure and depth.

The groups that investigated pressure vs. fluid density at constant depth/volume had inconclusive results. The pressure they measured varied by less than 1% between the three types of fluids. This provided an opportunity to discuss how the experimental technique can affect the uncertainty of the measurement. We discussed that with the new understanding of the relationship between pressure and depth, these groups could gather several measurements at various depths in each of the three fluids and compare the slopes of the resulting graphs to see if density has an effect. While we were discussing measurement uncertainty, we also discussed how the depth is defined not by the position of the bottom of the glass tube, but the water level within the glass tube. I learned of this important experimental technique in the article “Pressure Beneath the Surface of a Fluid: Measuring the Correct Depth” in The Physics Teacher. While the groups investigating the effect of fluid density on pressure applied their new experimental technique, the rest of the groups repeated gathering pressure vs. depth data while carefully examining the fluid level in the glass tube.

After a second day of measurements, students confirmed the linear relationship between pressure and depth. In addition, with the improved experimental design, students confirmed a relationship between pressure and fluid density. The results were not as accurate as I had expected. We identified a couple of additional errors that may have contributed. One, a couple of groups lost the seal between the glass tube and the plastic tube connected to the pressure sensor when the glass tube was in the fluid. This results in the fluid filling the glass tube and future measurements are incorrect if the glass tube is reconnected without removing it from the fluid.

I asked my TA to minimize the known sources of measurement uncertainty, perform the experiment, and determine how accurately pressure vs. depth could be measured. The slope of his pressure vs. depth graph was within 3.16% of the expected value. This is quite a reasonable result. If we used a taller graduated cylinder, I expect the error could be reduced further.

I’ll definitely do this paradigm lab again next year!

Projectile Motion Lab Practicum and Computational Modeling

In my AP Physics B class, I’m reviewing all of the material on the AP exam even though all of the students studied some of this materials last year in either Physics or Honors Physics. When we do have a review unit, I try to keep it engaging for all students by studying the concepts from a different perspective and performing more sophisticated labs.

When reviewing kinematics, I took the opportunity to introduce computational modeling using VPython and the physutils package. I started with John Burk’s Computational Modeling Introduction and extended it with my experiences at Fermilab where computational modeling plays a role in everything from the optics of interferometers to the distribution of dark matter in the galaxy. I then provided students with a working example of a typical projectile motion model and let them explore. I encouraged them to extend the model to have the projectile launched with an initial vertical displacement.

Later that unit, I introduced the lab practicum which was based on a lab shared by my counterpart at our neighboring high school. The goal of the lab was to characterize the projectile launcher such that when the launcher is placed on a lab table, the projectile will hit a constant velocity buggy driving on the floor, away from the launcher, at the specified location. The location would not be specified until the day of the lab practicum. No procedure was specified and students decided what they needed to measure and how they wanted to measure it. I also used this as practice for writing clear and concise lab procedures like those required on the free response section of the AP exam.

All groups figured out that they needed to determine the velocity of the car (which some had done the previous year) and the initial velocity of the projectile. Some groups used a technique very similar to the previous year’s projectile motion lab where a marble is rolled down a ramp and launched horizontally. These groups fired the projectile horizontally from atop the table and measured the horizontal displacement. Groups that calculated the flight time based on the vertical height were more accurate than those that timed the flight with a stopwatch. Another group fired the projectile straight up, measured the maximum height, and calculated the initial velocity. This group was particularly successful. Another group attempted to use a motion sensor to measure the initial velocity of the ball as they fired it straight up. The motion sensor had trouble picking up the projectile and this group’s data was suspect. A couple of other groups fired the projectile at a variety of angles, timed the flight, and measured the horizontal displacement. Some of these groups later realized that they didn’t really need to perform measurements at a variety of angles. After gathering data and calculating the initial velocity of the projectile as a group, I asked the students to practice calculating their launch angle based on a sample target distance. I hadn’t really thought this lab through and didn’t appreciate how challenging it would be to derive an equation for the launch angle as a function of horizontal displacement when the projectile is launched with an initial vertical displacement. It wasn’t until that night that I appreciated the magnitude of this challenge and then realized how this challenge could be used to dramatically improve the value of this lab.

Most students returned the next day a bit frustrated but with an appreciation of how hard it is to derive this equation. One student, who is concurrently taking AP Physics B and AP Physics C, used the function from his AP Physics C text successfully. Another student amazed me by completing pages of trig and algebra to derive the equation. No one tried to use the range equation in the text, which pleased me greatly (the found candy discussion must have made an impact on them). As we discussed how challenging it was to solve this problem, I dramatically lamented, “if only there was another approach that would allow us to solve this complex scenario‚Ķ” The connection clicked and students realized that they could apply the computational model for projectile motion to this lab. Almost all of the groups chose to use the computational model. One student wrote his own model in Matlab since he was more familiar with that than Python. With assistance, all groups were able to modify the computational model and most were successful in hitting the CV buggy. One group dressed for the occasion:

students ready to launch

Students’ reflections on this lab were very positive. They remarked how they appreciated learning that there are some physics problems that are not easily solved algebraically (they are accustomed to only being given problems that they can solve). They also remarked that, while they didn’t appreciate the value of computational modeling at first, using their computational model in the lab practicum showed them its value. I saw evidence of their appreciation for computational modeling a couple of weeks later when a few of the students tried to model an after-school Physics Club challenge with VPython. For me, I was pleased that an oversight on my part resulted in a much more effective unit than what I had originally planned.

Updated Measurement Uncertainty Activities

Like last year, we started Honors Physics with Measurement Uncertainty activities. Based on last year’s experience, last fall’s Illinois Science Education Conference, and this summer’s QuarkNet workshop “Beyond Human Error,” we made some minor modifications.

With the popularity of the LHC’s five sigma result, there was more of a context in which to introduce the concept of measurement uncertainty. I mentioned how calculus and Monte Carlo techniques could be used, but we stuck with the Crank-Three-Times method for this algebra-based class.

What was really missing in last year’s activities was how to estimate the measurement uncertainty when performing computer-based experiments. There are so many factors that contribute much more significantly to the measurement uncertainty than the computer-based measurement devices. David Bonner presented on “Learning Physics Through Experiments: Significance of Students’ Interpretation of Error” at the Illinois Science Education Conference last fall. One great idea I took away from his session was a simple and effective approach to addressing this challenge where students perform many trials to establish a range of values from which the measurement uncertainty is determined.

We rewrote the fifth station to introduce students to this method. Rather than using stopwatches, we setup two daisy-chained photo gates connected to a LabQuest 2 to measurement the elapsed time as a cart travels from the first gate to the second. The uncertainty of the LabQuest 2 is insignificant compared to other factors that affect the motion of the cart. Students performed ten trials and determined the measurement uncertainty from the range of values that they measured. We will use this technique throughout the year to estimate the measurement uncertainty.

Download (PDF, 35KB)

Holography Resources

This post is primarily for those teachers attending the Summer 2012 QuarkNet Workshop at Fermilab. However, other teachers interested in making holograms may find it useful; if you have questions, please contact me as you won’t have the experience of making your own hologram during the workshop.

Teachers at my school and, most recently, myself have learned how to make holograms in the classroom from Dr. Tung H. Jeong, a recipient of the Robert Millikan Medal from the American Association of Physics Teachers for his work in holography. After attending an AAPT workshop led by Dr. Jeong, I refined our techniques for making holograms and we started making transmission holograms in addition to reflection holograms.

When introducing holography to students, I start with a video from the How It’s Made TV show about holography.

I then introduce the holography and advise students how to select objects from which to make a hologram. The slides I use are below.

Download (PDF, 810KB)

We order all of our supplies from Integraf, which is associated with Dr. Jeong. Integraf has several tutorials on their web site which are essential reading:

  • Simple Holography should be read first. It describes all of the basics of making reflection holograms with many aspects applicable to transmission holograms as well.
  • How to Make Transmission Holograms. I prefer to make transmission holograms as they have several advantages over reflection holograms. The only disadvantage is that they require laser light to view. However, given how affordable laser pointers (green are best) have become, this disadvantage is becoming less significant.
  • Instructions for JD-4 Processing Kit. I believe this PDF file is the most recent version of the instructions. Similar directions are on the website, but the timings in this document are slightly different.

Supplies

  • PFG-03M Holographic Plates (2.5″ x 2.5″, 30 plates, $105, Item #S3P-06330)
  • JD-4 Processing Kit ($17, Item #JD4)
  • Holography Diode Laser (650nm (red), 4mW, $36, Item #DL-4B)

A previous post on holography describes how I setup a station and has several pictures.

Reflection and Refraction Activities

We are currently in the midst of the geometric optics unit in my honors physics class and just finished waves, which includes reflection and refraction, in my regular physics class.

My colleagues and I have developed a series of reflection and refraction activities that provide a shared experience that can be leveraged as we explore reflection and refraction of light. In addition, students find these activities engaging and they generate a lot of great questions.

I hope you find a new activity that you can use in class.

Here are the handouts.

Download (PDF, 41KB)

Download (PDF, 38KB)

I don’t have photos of the reflection activities, but I think they are pretty self explanatory. If not, ask, and I’ll clarify.

I do have photos of the refraction activities. I need to give credit for the first activity which is a recreation of an AAPT Photo Content winner from a few years ago.

Colored paper behind glasses

Colored Paper behind Water Glasses

Pencil in air oil water

Pencil in Air, Oil, and Water

Toy car in beaker 1

Toy Car in Round Beaker

Masses Hiding in Fish Tank (Total Internal Reflection)

Resources for Middle School Science Activities

When I visited National Instruments and shared my experiences with STEM in high school, a talked to a few friends who were involved in various types of science programs for middle school youth. They were interested in activities they could use to help develop fundamental scientific understandings (such as scale) as well as be engaging and provide an opportunity to learn about various phenomena. I don’t have any experience at the middle school level, but I reviewed the various projects that I’ve done (or hope to do) with high school students either in class or as part of Physics Club.

If you have a few favorite activities that would be appropriate for these students, please leave a comment. I’ll pass along a link to this post to my friends back in Austin.

Science and Engineering Projects

Scale

Citizen Science

Great resources:

N3L Activity Stations

While the Newton’s 1st Law activities serve as a fun and short introduction, the Newton’s 3rd Law activities provide a shared experience that spans several classes. The activities that the students explore are selected to highlight the most common preconceptions that students have about Newton’s 3rd Law. I stress how important free-body diagrams are as a tool in their physics toolbox and that, once they are adept at drawing free-body diagrams and once they actually trust their free-body diagrams, they will be able to explain a number of counter-intuitive situations. I introduce these activities by stating that Newton’s 3rd Law is one of the most easily recited laws of physics and yet is least understood. Here are the activities:

Download (PDF, 35KB)

Sequential Spring Scales

Sequential Spring Scales

The spring scales are initially hidden under the coffee filters. Only after students make their prediction are the coffee filters removed. Most students do not predict that the spring scales will read 10 N. Some predict 5 N (the spring scales split the weight). Some predict 20 N (10 N each way adds up to 20 N). In addition to drawing the free-body diagrams, this scenario can be explored further by asking students to predict the reading on the scales if one of the weights is removed and the string is tied to a clamp instead.

Bathroom Scale

This station provides an important shared experience that we will refer back to when discussing the elevator problems later in the unit. This station also generates a number of excellent questions such as “would the scale work on the moon?” and “how could you measure mass on unknown planet?”

Twist on Tug-of-War

tug-of-war

Students were very interested in this station this year since they were in the midst of Homecoming Week and inter-class tug-of-war competitions were being held. It may have been the first time free-body diagrams were used in the planning of the tug-of-war team’s strategy. The dynamics platform in the photo is a cart build from plywood and 2x4s with rollerblade wheels and has little friction. Most students claim that whoever wins the tug-of-war pulls harder on the rope than the person who loses. Only after drawing the free-body-digram and trusting it, do they realize this is not the case.

Medicine Ball Propulsion

Medicine Ball Propulsion

This is a fairly straight-forward station. I often wander by and ask the students exploring it why they don’t move backwards when playing catch under normal situations. I also check at this point and see if they are convinced that the force on the ball by them is equal to the force on them by the ball.

Computerized Force Comparison

This is the most important station in that it helps students truly appreciate Newton’s Third Law. I setup several of these stations to make sure that everyone has an opportunity to watch the graph in real-time as they pull on the force sensors. This is the standard Modeling activity for Newton’s 3rd Law. For students still struggling to accept Newton’s 3rd Law while working through this activity, I challenge them to find a way to pull on the two sensors such that the forces are not equal in magnitude and opposite in direction. This activity also counters the misconception promoted by some textbooks (perhaps unintentionally) that the “reaction” force follows the “action” force. Students can clearly see that both forces occur at the same time. (We refer to paired forces according to Newton’s 3rd Law, not action-reaction forces.)

WALL-E and the Fire Extinguisher

Who doesn’t love WALL-E? I repeatedly loop through a clip from the WALL-E trailer. In addition to the questions on the handout, I ask students what is incorrect about the physics in the scene. This year, I also showed students this clip that Physics Club filmed several weeks ago: