Archive for the ‘Lab Experiments’ Category
I had been wanting to add a lab where the students determine friction on an inclined plane. Students seem to struggle with the complexity of the problem and I thought a good lab would help. I wasn’t really happy with any of the labs I found on the internet, but I also wasn’t really up for creating one of my own. (Having four preps really sucks the life out of your creativity.) What I decided to do was to put the kids into groups, give each group a variable inclined plane (exactly the one in the picture), a couple of blocks, and lab weights. On the board I drew the force diagram of the block on a plane being pulled upward along with the appropriate formulas. The goal of the lab is for the students to be able to calculate the coefficient of friction between the incline and the block.
I gave the class the following instructions:
“You are creating a lab for next year’s students. You are going to need to decide on the lab procedure, required data and graphs, and the analysis questions. You need to write up the procedure and the lab results, but I only want one per group. I am going to take the best parts of each of your labs and use it next year.”
I asked them to start with only a single block, but they could add another if they think it will improve the lab. We discussed setting the incline from 0 to 40 degrees in 10 degree increments. They are using their phone to take pictures to include in their instructions and write-ups. They have one more day and then the paperwork is all due at the end of the week. I’m hoping for work that is a step above their usual lab write-ups.
I’m thinking maybe I lied to them. I originally did want the students to create a lab for next years’ students, but I might just give next years’ students the same assignment.
Our school has added a number of iPad and Mac carts. The technology push is on and I’m not generally excited about it. You have to understand, I am the technology guy. I sold top of the line engineering software to the defense and manufacturing industry. I’ve presented technology solutions to the Secretary of Defense’s office, Senators, Congressmen, Admirals, Generals, and heads of fortune 500 companies. I am not afraid of technology, I love technology. I have an engineering degree; I can program in half a dozen computer languages, and I’m competent in 3-D CAD. But handing me an iPad and telling me to use it in class is like buying a 12-piece screwdriver set and hoping screws will suddenly get loose. It’s a solution in search of a problem.
It took a brain-storming session with my department head to realize I do have a screw loose, I have a problem that technology might just solve.
I have been really unhappy with lab reports. I’ve gone full circle with what I want from the kids. Here is a brief history:
- Year 1-2 – The students were required to have hard-bound composition notebooks. Students were required to type the report (3-4 pages) and the notebooks were graded. I had about 100 students – grading was a nightmare and the work was poor when it was even done. Many of my students didn’t have a computer or a printer a home.
- Year 3-4 – I changed over to one-page labs where the students would fill in responses as they went. They were much easier to grade, but the rigor was gone.
- Year 5-7 – Students purchased Carbonless Lab Notebooks. They were to record observations and show their work as they went through the lab. This never worked as planned. It was a constant battle to get them to only write in the lab notebook; they wanted their report to be neater, so they took notes on the handout. Reports were hard to read because I was reading a copy of unreadable students’ handwriting. Students didn’t like that they couldn’t edit, mistakes were to be crossed out.
It is time for a change, again. Maybe technology will by my answer this time.
Here is the plan as it currently stands (in my head). Students will be given a basic report layout on the Mac using iBook Author. They will build on the layout to construct a full lab report. Having the Mac in their hands during the lab will allow them to take pictures of the set-up and the results. Ideally, they will be able to record data directly into tables and turn it into graphs, charts, and anything they feel is appropriate. Reports will be turned in electronically. What they turn in will be a unique, well-documented report, hopefully of a much higher quality than I received in the past.
The down-side is quite significant. First, there is going to be a learning curve for iBook Author. Second, the students don’t have their own Macs, so the entire lab report will have to be created during class time. What was a one-day lab will probably turn into two or three days of class time. Third, I’ll have to figure out how to transfer data from the Vernier to the Mac. I’m hoping the quality the iBook reports will make up for the lost teaching time.
If you are a follower of this blog, you may have noticed I posted this entry and then promptly unposted it. I thought the software I saw demonstrated was called iBook, but I couldn’t find the application for the iPad. I spoke with my principal today and she confirmed that I had it right. However, the authoring app does not exist on the iPad, only on the Mac. When I went to download the app for my Mac, it said it needed to be running OSX 10.7.4 and I’m running 10.6.8. I tried to update my Mac but it says no update is available. I admit, I’m a bit confused. The tech guy from school is the one pushing the app, so I’m sure he will get everything taken care of once we are back. I was just hoping to spend some time this summer exploring this idea.
If this works out, I should have some really nice files to post here in about two months. I’ll let you know either way.
I recently picked up a Sony Bloggie camera on eBay for about $50. It’s the same thing as a Flip camera. Make a video, flip out the USB plug, transfer file. It’s just that easy. I set up a backdrop of black paper from floor to ceiling. Kids got on a desk and dropped things. Everybody had to drop a golf ball first. A golf ball will fall pretty close to an ideal parabola, very little air resistance over such a small distance. After that, they could drop anything that wouldn’t break. I have soft squeeze balls and practice whiffle golf balls, superballs and paper balls, and best of all, a coffee filter. The coffee filter is a must, it reaches terminal velocity almost instantly.
We are using Logger Pro software from Vernier. I suppose you could use Tracker, but I have Logger Pro and know how to use it. In Logger Pro, we insert the movie file and then use the tools to place a dot on the object as it drops. The software advances the frame, and in a few minutes we have a synched up video, graph and data table. The software allows the students to quickly see how the slope of the distance vs. time graph changes. They can replay the image and watch their data points in action.
I have them use a quadratic curve fit to calculate the actual acceleration. Then the kids create a second curve and override the fit value with g/2. That puts the expected acceleration curve next to the actual. The effects of air resistance are instantly visible.
We just did this lab for the first time yesterday and today. Give the kids time, it’s going to take them a couple class periods to make this all happen. Initial feedback has been good. I think it’s making sense to them. They can see the effects of acceleration. They can clearly see terminal velocity.
Here is the lab they used. I expect there will be some changes.
I’ve been a member of American Association of Physics Teachers for about 6 years now. If you teach physics, please join! The journals and posters alone are worth the tax deductable annual dues. I attended my first AAPT meeting a couple of weeks back. I learned one or two great new things, met some super people, but I was also a bit disappointed.
Let’s get the negative stuff out of the way.
- I’m used to NSTA, so maybe my reference is unfair. AAPT was small, really small for a national conference. I felt like everybody knew each other because it was the same people every year. You could get through the entire exhibit areas in about an hour.
- It also felt like the conference was aimed at college educators. I know the organizers claim it’s not, but I’m giving my opinion here based on attending one day of a much longer conference.
- I had hoped that the talk on video in the classroom would give lots of useful tips; how to integrate video, success at flipping the classroom, etc. Most of the discussion was why video lectures won’t replace colleges.
Now the positives:
- The first timer special and lunch was a great idea. Lunch and the company was terrific, I’m glad I went. The first timer $75 one-day special is a great way to try it out.
- I got to meet some great people, some new, some who I had previously met online (Kathy, Frank). Everybody was warm and there to interact and learn from each other.
- I met local AAPT members who are trying to suck me in to local activities. I am interest, but they always do them on a Friday night and Saturday. I may submit, I do need local physics buddies but I love my weekends.
- Andy Rundquist demonstrated a great use of Jing. He has his students take a picture of their homework, then narrate the work on video. The video is their homework submission. Jing limits them to 5 minutes and when they talk, you can immediately tell if they know what they are talking about. Andy has them do this for every homework, I’m going to use it sparingly. Super idea.
- There is free software out there called Tracker that does video analysis. One cool use was to take a moving object, like a person jumping into the water, identify several points (hands, feet, head) through each frame, and let the software determine the center of gravity and plot the motion. Did I mention free?
- I really like the sessions where there is a new presenter every 10 minutes. Lots of great stuff, and if it isn’t, it’s only 10 minutes until the next one.
AAPT was worth my time, I wish I had done the entire week. It was close enough to home that I was able to take public transportation. Here’s the problem: if you can get your school to pay for you to travel to one national conference, which do you choose – AAPT or NSTA?
For me, it would be an easy choice. NSTA has so much more to offer, so many more strands, talks, exhibitors, and people to interact with. I would love to do both, I don’t see how. I will get involved locally, AAPT is too good of an organization to ignore, they are worthy of our support.
This is not a new topic for me, it’s been a burr in my saddle for some time now. All of the introductory physics textbooks address significant figures in much the same way. The problem is – nobody in the “real world” uses sig figs. At the same time, introductory physics isn’t the time to introduce complex error analysis models.
I’m having this discussion with Andy Rundquist of Hamline University. I asked Andy how they handled this at the college level. He told me they don’t teach significant figures and pointed me to a very lengthy article discussing why significant figures are all wrong. The article suggests the use of Monte Carlo analysis its place. That may make sense on a lab, but not on classwork and homework problems. The uncertainty article did have a suggestion; use six significant figures for calculations and round the final answer to three sig figs. The article does a good job explaining the reasoning, and I’m fine with it. The three extra “guard digits” preserve the accuracy, and the rounding makes the answer more reasonable.
- I will project an archery target on the board.
- Students will move back about 20 feet and shoot a round of Nerf darts at the target. They will be far enough back that most of them will shoot a 6, or 7 and not a 9 or 10, at least at first. Each student will take a turn.
- We will plot the overall results. We should get something resembling a normal distribution curve, but I won’t tell them that.
- I will ask the kids to average the data and come up with a value of x.x +/- y.y and start a discussion on whether or not that represents the data.
- We will then put a ring or other object on an electronic scale and write the mass with the error in the same way.
- After some discussion, I will bring up slides of normal, rectangular, triangular, and maybe exponential distribution curves. I want them to discuss the fit of the models to the data.
- My goal is that they understand that error is probability.
- About a week later we will drop rulers and calculate individual reaction times. This would be a good time to bring back the distribution graphs and perhaps even input our data into a statistical analysis program to find the best fit.
I think this will work and go over well. I’d love some feedback. It’s a first pass, what did I miss?
I never loved my pulley lab. I was never pleased with the learning, the kids seem to focus on trying to set up the pulleys and not on what is happening.
Two days ago I handed them this revised instruction sheet: Pulley Lab Rev D – Discovery Lab. The instructions are simple, “Your job is to come up with a set of rules that explains what is happening with the pulleys, ropes, and weights.”
Besides the ring stand, support, pulleys, weights, and string, I gave each group a Vernier and force meter. They set to work trying to figure out what is going on.
After they finished with the first setup, I asked them to tell me what happened. The weight was the same, so what was the purpose? Finally one of them said it changed the lifting up to pulling down. So a single pulley can be used to change directions. I gave them a few applications, like pulling something up into a tree or the mast of a ship.
Next they started on the other pictures. They noticed the force changed. I mentioned that there is a cost to the reduced force, what is the cost? Their response was less work. No, work is conserved. Keep going.
When they got through picture 3, I explained that they were experiencing Mechanical Advantage. If you hang by one arm, you hold all of your weight. Add the second arm and you are splitting the weight. Add a third arm… you get the picture.
As they got through the rest of the diagrams, two challenges remained: 1) what is the cost, and 2) figure out how to rig this up to get a mechanical advantage of 5. I gave them a hint – picture 2. They worked for a while without success. End of the first day.
I came into class and was pleasantly surprised to see all of the groups were already set up and working. They were twisting the ropes all over the place. I gave them 15 minutes to play. They still didn’t understand the cost, so I drew the solution for the MA of 5. We put a bunch of weights on the pulleys, almost 10 lbs, and I had them all take a turn lifting. I wanted them to experience the mechanical advantage. Then we measured how far the weights moved and how much string was pulled to make this happen.
That was all it took, they got it. In a perfect system, work is conserved. This led to a discussion of efficiency and how a lever also provides a mechanical advantage. It was a good day.
Note: Here is the solution to the challenge at the end of the lab: MA 5 Solution
When we did the egg drop challenge a couple of weeks ago, I asked the students to write about their design and the concepts involved in safely landing the egg in their structure.
For them, they had fun and were rewarded for their hard work with no lab report, just a dialog of what they built, why they built it, and the concepts we’ve been studying. I wanted them to talk about forces, gravity, momentum, impulse, collisions, and any other concept we’ve studied in order to explain the physics behind the effort to save the egg.
I’m thinking the egg got off easy. I had to read phrases like “depending upon how fast you dropped the egg,” and “the impact of momentum, ” and best (worst) or all, “the egg has many things to be concerned about it not to break”
Other than labs, I haven’t given a writing assignment before and I now think it needs to be a regular event. Clearly the students can not talk about the concepts. Although we spend weeks problem solving, discussing, and working in the lab, they can’t put the concept into an intelligent sentence. How did this happen? I feel like I’ve failed.