Sunday, October 16, 2016

Forces Match Graph: The Presidential Election Challenge


I developed an activity using force sensors to create a visual representation of Newton's Third Law.

The activity includes a brief exploration of the force sensor, then engages students within lab groups to conduct miniature tug-of-war sessions using the force while the computer records force vs. time data to plot a real-time graph.

The symmetry of the plots revels that whenever one object exerts a force on a second object, the second exerts a force on the first that is equal in magnitude and opposite in direction.

The plot also resembles the "probability of winning" graphs produced by Nate Silver's FiveThirtyEight team.

So I challenged early finishers of the lab to try their hands (literally) at reproducing the Presidential graph using force sensors. I thought the students did a fine job of it.


Here's the student sheet for the activity. It's adapted from the one included in the Conceptual Physics lab manual authored by Paul Hewitt and me.

The Force Mirror

Nate Silver's graphs can be found at FiveThirtyEight.

Reliant Robin Revisited

To accommodate a school-day administration of the PSAT this Wednesday, classes will meet for 20 minutes. What can you do in 20 minutes? Last year, I developed a mini-lesson around Top Gear's segment on the Reliant Robin.

I added a few questions to that lesson this year. I feel best when there are a nice, round 10 questions.

Access the video here (I recommend downloading videos for classroom use):
Top Gear's Reliant Robin

Oh, and I did figure out how to post the video here for additional convenience. Isn't it nice to learn?


Updated question set and answer key:
Rolling through Roundabouts in a Reliant Robin

What do you do with a 20-minute class session? Let me know in the comments.

Thursday, October 13, 2016

Traffic lights

Years ago while I was at the Exploratorium Teacher Institute an employee came in and had managed to get a bunch of real life traffic lights. They had asked a city worker who was changing them out what they were going to do with them and ended up walking away with a lot. I took home two green and one red and unfortunately left them to sit in a box all these years. I finally managed to check with Zeke Kossover about wiring them up and was surprised to learn that they ran off only 120 V. I had it in my head that they would need much more and I would have to use a transformer. So I bought a heavy duty plug for each light and hooked them up. You can find traffic lights of all varieties on eBay. It was very easy and now I have three giant lights!

I'm not quite sure what I will do with them but I have some ideas:
- Use the red and green lights to indicate to students when to keep working and when to stop on an activity.
- Use the red and green for a giant Colored Shadows demo (I haven't tested if this works yet).
- Have students use light sensors to investigate the light intensity at different distances. I expect that this is bright enough students from all over the classroom will be able to take data off this one light source. 

What are some other ideas about what I could do?

Monday, October 10, 2016

PVC Dart Dun Lab tips

I've written about making simple PVC dart gun shooters and how to use them in the classroom with NGSS. I just did this lab with my Physics students, after their projectile unit test because they did not have to calculate projectiles shot at an angle. It was a way to work in a design challenge with my students while letting them explore angled projectiles.

Students were shown how the shooter works and asked to find the largest horizontal range. They were to record their angle, launch height, etc. and discuss the design changes in between each trial. No additional questions, no conclusions, just a quick and fun experiment about experimental designs.

"Can we stand on the tables Mrs. B?" Sure!
"Can we pull the balloon back all the way?" Sure!
"Can we cut the straw?" Sure!
They just had to record how far it went and how they changed their experimental design.

Seven classes did this lab between my partner teacher and I, usually students worked in partners, spread out across the quad of our campus. We had a running record during the day to see who could in fact make it the farthest. The first few classes hit 38 m, later classes had an unconfirmed 53 m but the largest confirmed was about 45 m. Doing the experiment with so many older students we ran into a few new problems I'd like to warn you about:

Use brand name bullets.
A quick Amazon search brings up lots of refill sets for the small Nerf bullets you need. We opted for a knock-off brand and got 200 bullets for $20. We expected to be set for life as I had previously only broken one Nerf bullet out of 20 with three classes of freshmen testing it last year. We were wrong. Bullets would tear after a single firing, the orange tip would come off upon impact and sometimes even just indentations on the side above the straw was enough to get poor results.

Have extra balloons.
Some of my football players decided to get into a "who can pull the balloon the farthest" contest and frequently broke their balloons. Sometimes it just happened in the course of the experiment. Have lots of extra balloons on hand to repair shooters with duct tape. We tried to use the same size and same thickness balloons for consistency. A few students noticed that the replacement balloon wasn't exactly the same length as before and might change their experiment. 

Careful with metric tapes.
I have one 50 meter windup tape, nine 10 meter windup tapes and one trundle wheel. By the end of the day I had to completely unwind the 50 m one in order to rewind it correctly and we were down two 10 m tapes. Students did not understand how far 10 m was and would run out the tape with such vigor they broke the internal spindle of the tape. They can not be wound again, if you shake them you can hear all the broken plastic pieces rattle around the inside of the case.

The trundle wheel was far superior for measuring and was easier to reset in between trials. Although I did have one student hole the trundle wheel at arm's length straight out parallel to the ground and asked how it worked. He kind of sighted along it, maybe he thought it was a laser level??

Saturday, October 08, 2016

Inertia Ball Demo

Many people have some version of this Inertia Ball (available from Sargent Welch, and more) and may use it for an example of inertia similar to how I have in the past. There are several videos online including this one that demonstrate the classic demo (although I don't mention tensile strength yet):
This year I asked students in groups to predict what would happen before I did it. Students were to take a few minutes of discussion; some students came up to inspect the string and gently lift the ball to see heavy it was. I asked each group to share out what they thought would happen when I pulled the string slowly; the majority of the groups correctly guessed that the top string would break. After I did the demo I asked students to discuss again what would happen if the bottom string was pulled quickly. This time groups were split, some saying that the top string would break again and some that the bottom string would break. At this point I introduced students to the word "Inertia," they had not been introduced to it before although several already knew it and start singing the "Bill Nye: The Science Guy" introduction song.

Many of these inertia balls also have a third loop on the side of the ball. I ask students what would happen when I pulled the string from this loop directly to the side. "Are you doing it quickly or slowly?" they ask and I tell them they can think of it either way but when they share out they will have include their choice in their description. Again groups are split, some think that if I pull slowly the top string will break again, others think that if I pull it quickly the side string will break. I pulled the side string slowly at first and students saw the ball shift to the side but the top string held. I briefly said that this looks like a force in the horizontal direction did not affect the vertical direction. I reminded them that we saw a similar directional independence in our projectile unit. I let the ball hang freely again then pull the bottom string quickly and it breaks.

During my first period of the day while students were discussing I decided to add to this demo and make a tennis ball with the similar three eye hooks. I hung the ball and asked the students what they thought would happen if I pulled on the bottom string. Again I let them choose if they would like to think of it being pulled slowly or quickly. This time the top string breaks regardless of the bottom string being pulled quickly or slowly. Without prompting students start discussing why it happens, "Its not heavy enough!" or "See, I told you, it didn't have enough inertia."

While I gave these instructions on my whiteboard I made a powerpoint that has a visual for students as well as the questions.

For high school teachers, this connects well with the NGSS Science & Engineering Practices. Below are the excerpts I thought were most aligned to this activity:

Asking Questions:
O that arise from careful observation of phenomena, or unexpected results, to clarify and/or seek additional information.
O to clarify and refine a model, an explanation, or an engineering problem.

O Develop, revise, and/or use a model based on evidence to illustrate and/or predict the relationships between systems or between components of a system.

Monday, October 03, 2016

Stithsonian YouTube Channel

Doug Stith is also part of the Exploratorium Teacher Institute and has been sharing videos on his Stithsonian YouTube Channel with us for awhile. He has quite the knack for producing simple, clean videos that demonstrate concepts. He writes these for middle school students but the phenomenon he focuses on are usually quite complex. They are great for showing to your classes and he's always adding more.

He just posted this one on two Hot Wheels cars and their free fall motion that would have stumped my high school students for a bit:
He often creates puzzling videos to teach his students how to observe. There are some that ask students to spot the change or "what's wrong here?" and others that are forward/ reverse and stduenst have to guess which this Seesaw puzzler:

was followed with the solution:
He has quite a few up there on a variety of topics; peruse as you wish and let him know if you find them useful!

Air Pressure Rocket on a Hot Day

I use my Arbor Scientific Air-Powered Projectile rocket every year. With my Conceptual Physics students we take the data as a class, determine the average time and use that to calculate the maximum height. With my older Physics students this year I decided to open it up. I told students how the rocket worked and asked them to write their own procedure to find the maximum height and initial velocity. Not surprisingly, groups independently determined that the best way to determine this information was to time the rocket's entire flight and then use half that flight time to determine the rest. Once students determined how they were going to test it, we went out to an open space and launched the rocket five times with the "low" washer and five times with the "high" washer. Each group collected their own data for their calculations but then I collected their results for each period.

I noticed during three periods of trials that the rocket launched sooner later on in the day. In the morning the rocket consistently launched after 5 pumps with the "low" washer and 7-8 pumps with the "high" washer. By the afternoon it launched after barely 4 pumps with the "low" and 5-6 with the "high." It was a warm day so temperature definitely played a role. Looking at archived temperature data for our area it was about 82 degrees for the first period's data, 90 degrees for the second and 97 degrees for the third. If you look at the consolidated data for all three periods you can see that the maximum heights and initial velocities decrease as the day went on.
My last period did get a chance to try the "super" washer. Now I wish I had tried it in the morning for comparison when it was (relatively) colder. 

There are lots and lots of things you can do with this rocket. There is an additional set of wood angled blocks for consistent angled shots you can purchase.

Monday, September 26, 2016

Vernier's Ball Toss Lab

I decided this year that if I was going to continue to take the time to teach students how to interpret kinematics graphs of motion (displacement-time, velocity-time and acceleration-time graphs) I was going to bring them up more often during the year. As we transition in my class from basic kinematics equations to projectiles I was looking for a lab that did just that. This is where it pays to keep more resources than you currently use in your curriculum. I found a pdf I had downloaded from Vernier using motion detectors and a ball. The lab looked simple enough and I tried to reproduce the results myself.

The original instructions had called for a wire basket to be placed over the motion detector to protect it from the ball's return. I tried this with a tennis ball and found it very difficult to get the tennis ball to go up and down directly above the sensor. After lots of attempts (seriously like 50)  I was able to get three sets of data to work with:

I wanted students to see what happened at the max height on both the displacement-time and velocity-time graphs and understand what it meant. I wanted them to identify the time that the ball was still being accelerated upwards by their hand (easier on the velocity-time graph by the way). I wanted students to see a constant slope of the velocity-time graph to remember that gravity is constant. I liked how it was coming out but still wanted to make sure that students had an easier time than I did with this lab.

After tweeting to @VernierST I was able to get a few suggestions that made it basically fool proof:
1. Instead of a small tennis ball use a larger basketball (more reflective surface for the sonar).
2. Instead of a wire basket, which I didn't have enough of anyway, try putting two books on either side of the sensor.

Since my books are shorter I had students put two books on either side of the sensor as it was facing up on the table-top (above a picture from their lab). Students got great results and were able to focus more on analyzing the graphs using the tools in LoggerPro. Below is a sample set with the points I asked students to mark in their lab. Overall the lab was actually pretty quick and reliable. I think I could even move up the timing of the lab in my unit as an introduction to gravity rather than a review. Here is the lab I used.

Simple Machine for the win!

Being in California my family takes the drought pretty seriously. We haven't watered our front or back lawn in years. And unfortunately it looks like it. To increase the curb appeal and still keep our water usage low we decide to convert much of our lawn to drought tolerant plants on drip with mulch. As part of the conversion we had to cover 792 square feet with cardboard, overlapping a foot or more at each transition, as a compostable weed block. Even with the start of school I couldn't collect enough cardboard boxes at school to do the job so we ordered a roll of cardboard 6 feet tall and 250 feet long. While it wasn't heavy per se, it was pretty awkward to roll out the 20+ foot lengths I needed.  I had an old diameter wooden closet rod that was over 8 feet long so I shoved that through the middle of the roll and raised it up on two sawhorses.

Since it was above the ground I could easily pull on the end as far as I needed to and the cardboard would roll right off. But then I noticed that the whole roll, well, rolled. In the photo you can see the closet rod was pretty close to the back (right) of the sawhorse. It had started even closer to the front (left). Every few rolls I would have to readjust the rod on the sawhorse and bring it closer to the front. It didn't roll much but every 20 feet or so I would have to adjust it.

That got me thinking. This could be a great example for a Physics class that discusses the Mechanical Advantage of simple machines.  Ask students why the rod rolled, why didn't it roll very much? Usually the "distance in" is the "effort force" which would be the axis in the middle, in this case the closet rod. The "distance out" is the "resistant/ result force" which would be the whole roll acting as a wheel. This may seem backwards for this example since I was moving the wheel and observing the axis roll as a result. Students could calculate the Ideal Mechanical Advantage using the radius of the closet rod (standard 1.25" = 3 cm) and the cardboard "wheel" (2 feet = 30 cm). We would have to assume the machine is 100% to calculate it using distances and not forces.
You could expand the problem for students asking them about the circumference of the closet rod (axis) and how many turns before the rod might fall off the saw horse (assume its 18" wide).

Tuesday, September 13, 2016

Space Time Cord-inates

This is an example of a little idea that grew, changed and evolved and I'm still not done with it.

A colleague asked for some ideas about free fall and I remembered an activity often called Tin Pan Alley; here is a video demonstrating it. Usually done as a demonstration, hex nuts are tied to a piece of string and dropped from a tall height on to a pie pan or other metallic plate. The sound is better on a thicker reusable pie pan  than the thinner single-use ones. First students are shown a string with the hex nuts equidistant, say 20 or 30 cm. When the string is dropped the sound of each hex nut hitting the pan gets closer to the next hex nut than the last. A second string has hex nuts that are at specific (increasing) distances so that when it is dropped the sounds are equal times apart.

After suggesting this activity to my colleague I began to think about it more and decided to use it in my own kinematics unit. In what felt like a stroke of brilliance I thought of turning this teacher-led demo into a student run inquiry activity. I wanted to hand students ten hex nuts, a pie pan and some string and ask them to determine the distance of hex nuts that would create even interval sounds through experimentation. In the first draft I dashed off I actually titled it "Free Falling Nuts." After remembering I teach in a high school I realized it needed a new title.

But there was a sticking point, how can students be sure that the sounds are in fact even intervals? I decided to try and implement some technology.

I had downloaded the free Physics Toolbox app a few months ago and started to play with its many functions. Its an awesome app I strongly recommend downloading. There is a sound meter on there that records decibel levels over a time axis. I wanted students to use this free app to capture their hex nut hits so that they could compare the intervals between them. I also had Vernier Microphones and wanted to try using them as well. I wrote the whole thing up but before I decided to do it I thought I should try it. Turned out to be a good thing.

My colleague Matt and I decided to try it out before we gave the task to our students. We calculated the distances required for even time intervals with 0.1 s or 0.2 s, etc. and made a few prepared strings. We found that the sounds were so short that neither the Physics Toolbox sound meter nor the Vernier Microphones could pick up the sounds well enough to determine the time intervals. We tried amplifying the sound on a large stool, tried recording and slowing down the recording, etc. Without a 1:1 classroom we didn't want to rely on video analysis. We were forced to abandon the idea of students determine the distances by sound. And given that we wanted to use this as an introduction activity we didn't want students to calculate the distances between the hex nuts yet.

So I was back to the idea of a teacher-led demo. I decided to ask students to predict, discuss and then explain what they were hearing. I wrote this google slide presentation to guide the activity. The background data for calculating the distances for different time intervals is here, first calculated out by Matt. The larger the equal time interval, the longer the string. I was limited to a few meters given my ceiling height, something to keep in mind.