Yes, more on lab reports.  I don’t grade them right away, they just take a long time and I sometimes put it off for a week.  As a result, I get a bit confused about who was there and who didn’t turn in work and why.

I finally figured this one out, it has been the bane of my teaching existence for far too long.  Here’s the scenario:  I do a lab, tell them it is due in two or three days.  When I collect it, I don’t recall who was there that day, who worked, who just stood around, etc.  Now I’m missing lab reports, but I can’t recall if it is because they simply didn’t hand it in, they were out when it was handed in, or they were out and missed the lab.  In case you haven’t figured this out by now, paperwork is my downfall.  The solution that works for me is to create forms.

Excel to the rescue.  I made a form for lab day.  On the form I make note of who is present and who is out.  I also casually make notes on who is writing in their lab notebook or working on separate paper.  Some labs I want made up, others are a pain for me, so I exempt them if they were absent.

We’ve already been through the problem that I can’t attach excel pages on this blog, so I printed a pdf of one of the pages from my spreadsheet with my students’ names removed.  I have a separate page for each class so I only need to fill in the title, dates, and hit print.  I used this for the first time this week and I knew immediately who didn’t hand in work and who owed me work today because they missed school the previous day.  When I collect the work, I attach the form to the stack from the class.  For once, I am in control of lab reports.

Lab Attendance Forms

If you grade labs, you probably struggle for consistency and simplicity in grading those beasts.  I know I do.  I’ve come up with a more simple plan through a series of iterations.

I make up these little score sheets, they run nine to a page.  The idea is simple; the lab is worth 25 points.  Each problem is a deduction of usually one or two points.  I grade on the score sheet, then staple or glue the sheet to the lab.  I find that the feedback of lost points gives them a clear indication of what to fix for next time.

I like a 25 point lab for a number of reasons.  I tell the kids, every lab starts at an A+.  Each point deduction drops the grade by one third of a grade.  So a one-point deduction drops an A+ to an A, where a two-point deduction drops an A+ to an A-.  This system lets me choose a value for a section, so if there is a lot of calculations and graphing in the analysis section, I can make omission of the work worth a full grade with a deduction of three points.  I don’t take late work unless they were absent, so not handing in a lab isn’t fatal, but it hurts.  A 25-point lab is also a good buffer for bad quiz and test grades.

I have played with this over the last couple of years.  My first lab or two of the year I grade holistically, I get a feel for what I think it deserves.  Then I go back and count where I would have given deductions.  That is why I know this works for me.  A lab that is in order and complete is an easy A.  I establish certain requirements, such as each page needs the header completely filled in, each section must be present and in the proper order, formulas and calculations are written out, and the last page is signed as an indication they did their own work.  As they get better at the layout and report, I can up the standards on the actual lab work.

The attached page is a pdf of my spreadsheet.  Use mine or make your own, whatever works for you.

Lab Score Sheet

As always, if you have ideas to improve upon this or do something you like better, I really want to hear about it.  I’m tired of having to learn all of this the hard way.

Here’s a little end-of-quarter gift for you.  I’ve been meaning to post my excel gradebook and curving routine for some time.  I think some of you are going to want to send me a Christmas present for this one.  (And if you are so inclined, I’ll give you an address to mail it to.)

The gradebook isn’t really all that special, it just does exactly what I need it to do.  The second sheet has a few sample grades so you can see how I use it.  In a nut shell, here’s the idea:

• A line for each kid, you can do first & last names, I tend to do last, first in case I need to sort.
• Along the top is the graded assignment.  I often use a comment in the field so I know what the actual homework was for that grade.  It’s helpful when they were out and need the assignments.
• The column marked “Point Adjustment” allows me to exempt the grade for someone that was out.  You can see the example on sheet 2.
• I have the kids give me a code, like their birthday or address.  Then when I go to print, I hide the name, sort by the average grade (decending), hit print, then undo, undo.  Don’t sort the first column.
• You will see some boxes at the bottom, two stacked and ####’ed out.  That is the average and std dev.  When I give a test or quiz, I copy and paste one of those to the bottom.  It lets me know how the trend is going.
• If a kid is failing or near failing, I color their line red.
• You can keep extra rows, but make sure the averaging function is removed or it will include those zeroes into the class average.
• A missed assignment can be blank, it still counts as a zero unless you do a point adjustment.  I normally don’t take late work, so I just put in a zero for those, but it’s useful for kids that were out to see a blank. It reminds them to turn in the work that was due.
• When the quarter is over, I make a copy of the spreadsheet and store it under admin archives.  Then go back to my original and wipe out all the grades and start over.

What’s great about this program is I can make changes quickly, I keep it on my USB drive, so grades travel with me, I print grades at least once a week, it’s very quick to post grades on my bulletin board, and the kids keep me honest if I mess up their grades – which in the end helps both of us.  It’s much faster than our school grade book program, so I consider my spreadsheet the master if there is a conflict.

Now, the curve routine.   After a test that will need curving (and don’t they all), I copy and paste just the grades to the sheet labeled ’stuff.’  Once there, I sort them high to low and then use the Average function and the Standard Deviation function.  I really only want the average, but the std dev gives me an idea how spread out the grade pattern looks.  I’m in a bullet kind of mood…

• Look at the grades and the average.  I like my test averages to be 75-77, but they are usually like 60.
• Go to the Curve sheet.  Go to the yellow boxes.  Here is where you get to play a little.  Take the highest test grade and make it what you want it to be.  If someone stood out from the rest, I may make it 100.  If not, 95 works for me.  Now the low – I usually start out with the low grade being curved to a 50.
• Go down to the single yellow box and enter your current average grade.  Below it, you can see what the average grade curves to.
• If the average is below what you want, you can boost the curves-to grade for the high score or the curves-to grade for the low score.
• When you have it where you want it, change the title on the Curve sheet and hit print.  It will print the curve, plus what the high, low, and average curve to.
• To enter into the grade book, I usually make a new column called ‘curve’ worth no points and put the delta in there.
• Pointer (worth and extra dollar or two) – use the comment function and put the curve numbers onto the test.  You can see this on the period 3 sheet on the test dated 11/10.  This way, if I have to go back and recreate the curve, it’s a piece of cake.

What I’ve found is that by keeping my test average around a C/C+, I have just the right grade distribution at report card time.

Ok, WordPress doesn’t allow uploading spreadsheets, so I saved it as a shared google doc.  Go and get it, do a save as to bring it to your computer.

http://spreadsheets.google.com/ccc?key=0AtZmpkiMp_0qdFVuODJJQVFlZWxfdHoxUS1OVzR1c3c&hl=en

This is a pain in the butt.  If you go to the link, click on file, download, and save it as your own excel file.  If you prefer, just email me and I’ll send you the file directly.  There’s got to be an easier way, I’ll look into it.

I got an email from Jeff asking me to promote his new physics forum.  It cracked me up because he called me an influential blogger.  Don’t influential bloggers get free t-shirts, or hot nerd chicks or something.  All I get is more papers to grade.  (As an odd side comment, and mind you, this was an after thought, I did a google search for “hot nerd chicks” and was quite surprised at the brilliance of my comment.  Who knew?)

I did say I would help him out and post a quick article and the link.

I think there is a place for his forum.  It’s actually what I wanted to do here along with this blog, but WordPress doesn’t make it easy and I need low maintenance to do this blog.

As of today there are only four questions, but I can see it growing quickly.

Jeff Hellman’s PhysExchange:  http://physicsteachers.stackexchange.com/

Jeff, you owe me a beer.

Let me start by saying that the kids really liked this lab.  It made them smile when they succeeded.

I kind of made this one up, kind of adapted it from the electronic timer manual.  The idea is that we use a ramp to accelerate a steel marble, have it pass through timer gates, measure the distance between the gates and calculate the velocity.  Do that a couple of times for accuracy.

Now measure the height of the table using a meter stick.  Use a fishing weight on a string to find the point directly under the edge of the table.  We now have the horizontal velocity, the height of the table, we can calculate how long it will take to fall.  Next we do the math and place a penny where the steel marble should land.

In the beginning, it would works sometimes, but not always.  I determined that our heavy epoxy table tops caused the steel ball to bounce, losing some of its horizontal velocity.  The bounce was easily dampened by placing two or three sheets of paper under the end of the ramp.  We also had some issues with hitting the side of the photogate.  Lining up the gates with the ramp was a minor issue, but an important one.  After the speed was determine, we moved the photogate away used the already calculated speed.

Here is the Lab as I wrote it up, it needs some updates like the paper under the ramp.  I realized later that I should have had the kids measure the starting height of the ramp.  Then we could go back to it later when we do energy and analyze the results.

Horizontal Projectile

Next year I think I will have them hit the penny first time, then a dime, then a small washer, so each time it must be more accurate.

As always, comments and ideas are welcome.

I don’t know why I’ve never mentioned this before.  In my room I have a bookshelf full of mostly paperbacks.  The books are there for the kids to take, read, and if they chose, return.  I go to the public library every couple of weeks, they are constantly selling paperbacks at either 5 for a dollar or a bag for a dollar.  I must have about 200 books on my shelf right now.

I have lots of science fiction (Asimov, Bradbury, Clarke, Card), mysteries, thrillers (I love Ludlum novels), fantasy, even some non-fiction titles.  I have a bunch of the Sue Grafton series (“A is for Alibi”, etc.) since the protagonist is a woman detective.  I often recommend those to the girls.  I try to keep the books different from those they read in their English classes.  Books don’t equal homework.

I require nothing in exchange.  I ask them what they like, then I recommend something if I can.  Today a student took Stephen King’s Night Shift.  I pick up every copy of that I can find, it’s a great book and I recommend it frequently.

I even have one student who is constantly bringing in books her father donates to my library.

My goal is pretty obvious, get them to read something.  Anything.  If they are reading, they are learning.

I’m the first one to admit I don’t know everything.  (Actually, I’m the second, my wife is the first.)  I don’t know how to proceed at this moment, I’m throwing it out there for discussion.

We are using the carbonless lab notebooks, I like them.  I want the students to use a lab notebook, but I don’t want the experience of learning to be about rewriting a procedure.  I’m struggling with the whole idea that every lab starts out with a hypothesis.  My personal experience of learning often begins with “I wonder what happens if …” You could say that is a form of a hypothesis, but it is really just a quest for understanding the workings of everything.

The other day we did a lab where we used a ticker tape recorder to make a mark every 1/60th of a second on a paper strip.  The goal is to record the changing distance of a falling object and the constant distance of a constant velocity toy car.  I wanted them to see a visual record of acceleration, to understand the distance changes at each tick, and to graph the distances over time.  They struggled to write a meaningful hypothesis.  How could they write one, they don’t know what they are going to see.  I wanted to help them, but I felt that if I said too much, I would be revealing the discovery they should be making.

If labs are about discovery, and I think they should be, then how can they have a hypothesis?  How is it discovery if there is only one right answer?  If I make the lab all about them finding the right answer, then their focus is on what will get them a good grade, and not about learning physics.  I’ve looked at lots of lab report formats online.  They make sense if the experimenter is doing research on a topic where he or she is actively working.  Each bit of learning leads to a new question and a new experiment.  Here, the hypothesis feels contrived.

Would it be wrong to have a hypothesis that is just a general question?  Am I going about this the wrong way?  I think I’d be happier if they wrote, “We are hoping to see visual evidence that differentiates a constant velocity and accelerating velocity.”  If I head this way, am I failing to preparing them for college?

One thing I am changing; in the future they can reference the handout.  It’s a waste of their time and mine when they have to rewrite my instructions.  Yes, it forces them to read the instructions, but that’s not deep and meaningful learning.  The clock is ticking.

What are you doing?

Their homework assignment was called “One Question.”  Their job was to write one science question that they wanted to have answered, any area of science is fine.  If they were goofy or tried to be funny they wouldn’t get credit.

What I got back blew my mind.  There were such incredible questions that I’m going to assign this about once a month.  I’m going to talk about some of these during science news days on Fridays.  Some of them I will save for when we get to the topic.  Some I will post as a list questions they can research and present for extra credit.

Extra credit is a sore point for some of you.  My rule on extra credit is this: if you are missing more than two assignments that quarter, extra credit is not available to you.  Extra credit is not an out for the lazy, it’s a boost for those who work hard and need a couple more points.

[I left the papers at school, I'll post some of the questions next week.  My own blog is blocked on school computers.]

I hate them.

Parents hate them.  Most aren’t any more science literate than their kids.  The pressure on the parents to create a decent project is awful.  Coming up with a good science experiment project is really hard to do.  There are dozens of books on the topic and everybody is clawing at them, trying to find something they can handle.

Kids hate them. They see it as a grade, nothing more.  They don’t understand the need for the formality in the presentation.  All they know is they don’t win.  Now they hate science.

Teachers hate them.  Be honest, they are brutal to grade, the work is not worth the effort.  Please, no more volcanoes.

OK, now that I got that off my chest, let’s talk about this.

I love doing experiments.  I love inspiring kids to think.  I make my students experiment constantly.  I want them to play in science, find the joy and excitement.  I want them to ask questions and be curious.  I make them launch rockets and throw balls.  If they make a paper airplane in my class, they better make five or ten and tell me what design works best and why.  Is science really distilling everything they know about a topic and making it fit on a bent poster board?

I will be doing a science fair in my classroom in about a week.  Only I don’t call it that.  I call it my “Mythbusters Project.”  To be honest, I don’t care if it’s a stupid idea they are testing.  I want them to be goofy and have fun.  I help them to make sure they are doing good science.  I challenge their findings.  I make them work together and research.  I know, it’s not the county science fair.  So what?

You can’t sell someone something they don’t want or need.  Really, it’s true.  OK, maybe once, but you lost them as a customer forever if you do that.  Kids want to be creative, they want to think, they want to learn.  They are unbelievably curious.  If you don’t think so, leave a pile of mechanical puzzles on the table and don’t draw attention to it.  Every one of them will be in the kids’ hands in two minutes.  Try it.

Here’s the question you need to ask yourself:  What can I do to make this kid love science?

I was listening to my iPod this morning and I heard Neil deGrasse Tyson as a guest at a public symposium in Portland, Oregon.  It was published as part of the podcast “NOVA scienceNOW.”  I’m considering playing it for my class, it’s only 30 minutes long.

This sounds a lot like what goes on in my classroom on Fridays, only way more orderly and with microphones.  In my Conceptual Physics classes, my students have an assignment  on Wednesdays to print out a bit of science news, any area of science is fine.  They need to read the article and highlight key points.  I collect these and on Friday we have science news day, where we talk about anything science.  I use the articles as a starting point, and we quickly jump from topic to topic.  Nothing is off limits, they come up with a million questions.  Sometimes they go off and research something further from our discussions.

In addition to using this just to get them thinking about science, I use this to get across certain agenda items.  A couple of the news items were cut and pasted into word to make it easier to print.  I asked the kids to make sure they note the site it came from, I need the source so I can go back and read more.  We talked about good and bad sources.  Another student had an article on the 2012 predictions.  The first paragraph talked about some scientists needing facts, but the authors were going on “instincts.”  I did the pen and shoe drop, asking them about their predictions.  I emphasized that scientists guts can be a starting point, but facts are the only things we trust.

This week, an additional assignment is going to be to write a question about science that they have wanted to know the answer to.  I’ll may pick from those to get the conversation started or  I may put up a “great question” list and let them research a question and present the answer for extra credit.

I was going to imbed the podcast or attach the file for download, but WordPress wants me to upgrade from a free blog to do that.  Go to the iTunes store and search for NOVA ScienceNOW.  I tried the NOVA website, but they don’t make it any easier to link to the file.

Dr. Tyson has a couple of great responses.  One is about using his own children as an experiment in getting kids to be science literate.  It’s worth listening to for just that one.  There’s more, go listen.

After you listen to it, tell me if you would play it in the classroom.  I’m a little wary of audio only, kids tend to listen with their heads on the desks and it can be hard to get them back up.

Update - The kids enjoyed it.  At first, they were reluctant (no pictures), but I stopped it half way through and offered to switch to science news.  They asked in all three classes to continue the audio.  I know they like science news, so that was encouraging.  I think they honestly enjoyed the change of pace and learned a little something from someone else.

I’ve always found it challenging to get students to draw the problems.  I don’t understand their reluctance, I can’t imagine trying to keep the facts in my head, yet so many of them do just that.  The result is that they miss details and make mistakes.

Today I saw a simple problem that I thought I would use as an introduction to drawing problems.  The simple word problem says:

[Updated as used in class] There is a triangularly shaped park with trees along the edge.  There is a tree at each vertex.  Each side has five trees.  How many trees are there all together?

Very simple problem if you just draw it.  The answer is not 15.

I don’t know about you, but I want the grades in my class to mean something.  I’ve seen so much grade inflation in schools.  It used to be school policy that we weren’t allowed to fail anyone.  Thankfully our new administration is so much smarter than the old one.  I certainly don’t want to fail any students, but if they don’t do the work and don’t try, I don’t have a problem giving them the grade they’ve earned.  Two students didn’t graduate because they failed physics last year.  I think that is a powerful motivator for this year’s students.  I will show them my grades distribution the first day of class.  They can decide how hard they are willing to work.

Here is the spread of my grades from 2008/2009:

• 7 – A’s
• 38 – B’s
• 35 – C’s
• 8 – D’s
• 2 – F’s

At some point I will put up a post about grades and how I curve.  I even have a spread sheet program that helps me.

I love magic.  Being a scientist doesn’t take away from the amazement created by a well executed trick.  My father sent me a clip of Chris Angel doing a trick where he not cuts, but pulls a woman in half right on a park bench.  The trick is incredibly shocking, the people on the set are screaming in fear and surprise.  You can see they are visibly shaken.

YouTube video of Chris Angel. I’m going to show this clip and then start a discussion.  First question – did he really pull this woman in half?  Obviously that did not happen, so what did?  The students are going to either work alone or in small groups and try to come up with a way to explain and possibly reproduce the effect.

What I hope to get from this exercise is a little critical thinking.  If the woman was not pulled apart, and Chris Angel doesn’t have real magical powers, then it must be a trick.  We don’t know how he does it, but we can make educated guesses and then experiment to attempt to reproduce the method.

How do you see light’s path through a lens?  We did this experiment at the DAMOP teacher’s workshop at Penn State last year.  Make Jello in a flat bottom pan, about 3/4″ deep.  Use half the water so the Jello is firmer than normal.  You’ll have to experiment with the color and tell me which works best, I haven’t done this on my own yet.

Obviously the Jello is made the day before.  Now cut the Jello into the shapes of the lenses.  You can make prisms, double concave, convex, whatever you like.  You can float the pan in warm water to release the lenses from the pan.  Don’t do it too long, just enough for the Jello to lift out undamaged.

Now shine a laser pointer through the Jello.  You will be able to see the path of the laser and follow as the light is bent by the lens.  Set up a series of lenses and have fun.  When you are done, you can eat the experiment.

I’ve been searching for a curriculum and some ideas for teaching robotics.  I’m looking to build a course that is half a year of robotics and half a year astronomy.

I haven’t found very much so far.  Some stuff at Carnegie Mellon and constant links to Lego products, but not much else.  I’m looking to make this an elective the following year and I need to start figuring out how I’m going to make this happen.

Some of you must either teach this course or have someone in your school who teaches this course.

I need some help please.

Today is the 1-year anniversary of this blog and I get the feeling it has been rather successful.  I’m currently getting roughly 7,000 page views a month.  I never would have expected 78,000 page views to a physics teaching blog in a single year.  I guess I’m not the only one that needs help figuring out what to do each week.

Best of all, I’ve made some new friends around the world.  That’s just too cool.

Thanks for all the support and comments.  Live long and prosper.

Scott

I’m almost never out sick.  This is a good thing because my emergency lesson plans are, well, they kind of suck.  It’s motivation to come to work.  The few times I’m out, I either have the sub put on Mythbusters, or I email in a lesson based on our current work.

I would really like to have some better, stand alone emergency plans, but all I’ve come up with is Einstein’s Puzzle.  It’s a logic puzzle that takes quite a bit of thinking and time to solve.  I give extra credit for getting it right  (Einstein puzzle).  Just guessing isn’t enough, they have to show that they did the work or they don’t get the extra credit.

I need something else.  Maybe I’ll design some review worksheets of conversions or scientific notation, or maybe an SAT II section on Physics.  I’m going into my 4th year teaching these courses and that’s the best I’ve been able to do.

I need help.  Or an intervention.  What do you do?

Just a quick poll to help me understand who is stopping by my blog.

This is so cool, thanks for participating.

I received an email from a rep from Bedford, Freeman, & Worth Publishing (http://www.bfwpub.com/highschool) with their latest textbooks and a lab notebook that has carbonless copies.  I was intrigued since I’ve not been happy with my use of notebooks (see my post on Pulley Lab).  I really like the idea of the students using lab notebooks, and I do more than enough experiments to make it worth keeping one, but carrying 100 of them home to grade … it just doesn’t happen.

To make my life easier, I’ve created a bunch of mini-labs where they get a handout, answer questions and hand it in by the next day.  This has worked well from a grading point of view, but the students haven’t had to keep a lab notebook anymore, and so I’ve lost the college-level work I’m aiming for.

I think these carbonless copy notebooks may be the answer.  We are going to try them next year.  The students will be required to purchase them at the school store.  They are not inexpensive, the cost to the school is between $9 and $11 each.

Anyone using these?

You can find the link for the publisher here:  http://www.haydenmcneilspecialtyproducts.com/products/physical-science.html

I’ve been listening to Carl Sagan’s A Demon Haunted World on tape in the car and I’m awash with new ideas.

Next year, as part of the introduction to the scientific method, I need to draw a line on the board.  On the left, I will write “Gullible,” on the right, “Skeptical.”  If someone is totally gullible, they would believe that a cat matures into a dog.  It seems silly, but the idea is that a totally gullible person takes any statement as fact without question.  For a totally skeptical person, they would doubt you on absolutely everything you say and do.  The total skeptic is so annoying that nobody wants to converse with him.  Both extremes are no good, our job is to find a happy spot somewhere to the right.

Next, let’s talk about ESP.  Is it real?  Do you know anyone with ESP?  If we were gullible, how would we answer to the claims of a person with ESP?  What if we were skeptical?  Let’s accept the claim that ESP might exist.  How can we test it?

At this point, I want to break the students into groups.  Their job is to come up with an experiment to test some form of ESP.  They will need to write up their proposed experiment and then perform it the next day in class.  They will then write up their results and submit their report to peer review by their classmates.

Wouldn’t it be cool if they could decide good experiments from bad through the process of peer review.  I can’t wait to try this in September.

If you don’t know what a lateral thinking puzzle is, google it.  These are great puzzles to make the kids think a little differently.  The kids make so many assumptions, I’m always struggling to find ways to open up their thinking process.

I had a period to kill with one of my classes, so I pulled out a few of these puzzles.  It’s real important to lay down the rules for the puzzles.  They need to take turns asking questions, they get into it, but I can’t answer questions when they talk over each other.  The questions have to be in a form that I can answer with yes or no.  Sometimes I answer with “doesn’t matter” or “I don’t know” and that irritates them because it wasn’t in the rules.  It was, I just didn’t tell them.

The idea is for them to start asking questions and realizing they assumed an incorrect body of information.  Here’s an example, it’s so common, I don’t think I’m ruining any great puzzle sharing it.

The solution is usually in the form of a story that the kids need to work out through their questioning.  Here is the solution to the above puzzle:

A poor peasant from somewhere in Europe desperately wants to come to the United States.  Lacking money for airfare, he stows away in the landing gear compartment of a jet.  He dies of hypothermia in mid flight and falls out when the compartment opens as the plane makes it final approach.

Check out some online sources and books at the stores.  I have a couple of books, but I find most of the puzzles aren’t good enough to use in class.  I might highlight for or five puzzles from a small book of puzzles.  Tell me how they work out for you.

This mini-lab worked out really well.  In fact, quite of few kids surprised me by getting into building circuits.  I know a lab goes well when nobody bails or gives up in frustration.

I introduced series and parallel circuits with three quick overheads.  I also taught them the schematic symbols for a battery, switch, and bulb.  I helped them out by drawing the schematic for the first problem.  The attached document is pretty much self-explanatory, but I would suggest you have the kids read the last couple questions before they start building.

I had the kids in groups of two.  Each group needed a 3v battery pack (2-D cells), two light bulbs in holders, two knife switches, and about 6 sets of alligator jumpers.  You could use pre-cut wires, I had the jumpers available.

series-and-parallel-switches

With the introduction to series and parallel circuits, the lab took the entire class period to complete.

It’s not about being politically correct.  Limes are cheaper than lemons.  A bag of 5 limes was $1, lemons were $2.  Since we were sticking metal in them and then throwing them away, frugality wins.  Besides, I have some leftovers that may become margaritas.

Now, I ran out of time and didn’t create a lab sheet, so I had to wing this a bit.  We did have a kit from Carolina that included electrodes of Fe, Cu, Al, and Zn.  I decided I would have less trouble if I did the cutting into the limes.  I used a plastic knife and cut two slits about 3/4″ apart, large enough for the electrodes to easily slip into the lime.

On the board I created a simple 4×4 matrix of the metals and had the students test each metal pair as electrodes.  I also had them test Fe-Fe, and Cu-Cu, etc.  That meant they had to share electrodes to get the similar pairs.  They found that only dissimilar metals created a voltage and the voltages were not all equal.  Cu-Zn created the largest, at around .9 volts.

Next, I had them pull out change from their pockets and try the coins as electrodes.  I also had some galvanized screws (zinc coating) for them to use.

Once they had a feel for what makes their battery work, I gave them each an LED for them to try to light up.  A single battery didn’t have enough voltage, so they had to partner up with another group and figure out (with some guidance in the form of a drawing on the board) how to wire the batteries in series.  With two, they could get a red LED to light up.  We had to turn out the lights to make it visible.  The green LEDs seem to require more power and didn’t light up with the same batteries.  They also wired three together and made the light even brighter.

Yes, I needed more organization.  Tomorrow we do series and parallel circuits using switches and light bulbs.  It’s fourth quarter and I feel like I’m out of energy myself.

I now feel qualified to put something up on this post.  We played for two whole days in my physical science class, and the kids still want more.  Another day in my three physics classes, and I’m battle ready.

I began by showing the balloon on the bald teacher’s head and sticking it to the wall.  Trust me, nothing gets them going more than a mostly bald teacher trying to rub a balloon on his hair. Amazingly, there were quite a few students that had never seen a balloon charged up and stuck to a wall.

We then went to the standard acrylic/fur type of static charge, explaining how the charges separate.  I caused paper and bits of styrofoam to jump from the charge.

The van de graaff generator is exactly like those static creating devices, but it just keeps making more and more static.  Here are a few ideas I have either done or picked up on the internet.  One important note; I got all of the kids up and involved.  Some of them were scared, but after the girls charged up their hair without pain, the chickens were shamed into bravery.

Before doing each of these demonstrations, I ask the students what they think will happen:

1.  I take a bunch of holes from a paper punch and put them on top of the dome.  Then I turn the machine on and the holes fly up into the air.  The dome and paper, all having the same charge, repel each other.  The paper holes spray up in a fountain of white dots.

2.  I tape strips of paper to the dome.  The paper stands up and stays standing until the dome is discharged.  This is a good precursor to the hair thing.  They don’t expect the paper to stay up in the air when the machine is off.

3.   I use the grounding electrode to make the sparks jump really far.  Let the generator run until you hear the ozone crackling.  Then you get a great big spark.  I use this to build some tension and fear of the generator because I’m asking for volunteers to do the hair thing.

4.  Making hair stand up.  The student needs to stand on a plastic milk crate or something to insulate them from the floor.  One student wanted to try this standing on the ground.  I think he had sweaty feet, he said (and we heard) the discharge going through his feet into the floor.  I wish I could tell you how to know what kind of hair works best.  Really long hair is too heavy, really short hair is too stiff.  Hair color doesn’t seem to matter, although dark is easier to see than blond.  For some reason, the hair of the black girls worked best.  I’d love to post the pictures, but posting pictures of student’s is a no-no, at least without written permission.

5. Fluorescent light bulb lights up.  It does not need to come into contact with the dome, the spark jumping to the glass with light up the bulb.  We found that placing the bulb about 1 inch from the dome gave the best results.  Stand on a piece of wood or you will feel the shocks in your toes.

6.  We made a chain starting with one person charged up.  He touched the next person, but held on.  Now they both charged up and continued to another person.  If the person getting shocked was sitting in one of our desk/chair units, he or she got a constant stream of shocks to the legs and back side.

7.  Water bottle on top produces lightening like show.  I’m going to tell you to be careful with this one.  It works pretty well at first, but the massive sparking in the bottle actually burned through the bottom of the plastic bottle.  Once they started leaking, they wouldn’t charge up.  I had to use a different bottle for each class.  More importantly, the bottle kept the charge.  Just holding the bottle and moving it around gave a constant stream of rather painful shocks.  At one point I was holding the grounding rod and the bottle.  I touched where the bottle was leaking through the bottom and I got an extremely nasty jolt across one arm to the other.  Be careful with this one.

8.  A balloon placed near the dome is first attracted, then when it touches the dome, the charge is conducted and it is repelled.  The charge leaks off and this repeats over and over again.  I used this to lead into Coulomb’s Law and the force due to the electric charge.  Again, you will want to stand on something to insulate you or you will have toe sparks.

Here are a few demonstrations that I haven’t yet tried:

• Mini pie tins stacked on top fly away one at a time – the pie tins I tried were too big.
• Soap bubbles are repelled as they get near the dome.

Any more?

I’ve been doing this lab for a number of years, but it needed a make-over.  I did that today, it’s beefed up a little and I added a data sheet.  I’ve gotten away from the lab notebooks because they are just too hard for me to collect and take home, and I never seem to be able to grade at school.  I’ve headed towards more of a “min-lab” format that I read about in The Physics Teacher a year or two ago.  This has greatly cut down on my grading, which allows me to do more lab and hands-on work, which gives me more to grade.  Somewhere in there we reach equilibrium.

This lab uses two double pulleys, some mason line, a ring stand and ring,  spring scales, a meter stick and a weight.  I like to use a 1 kg weight.  It’s heavy enough that they can feel the difference when the pulley helps out, but not so heavy that everything is falling over.  I found it helpful to have two or three different size strings.  The short string for the first three configurations is about a foot long.  They then switch to a second string that is four or five feet long.  I would suggest you play with the lab and then make up the appropriate length strings.   I like the pink mason line, it’s easy to see from across the room, so I can tell what’s going on at every work station.  It’s also easy to find when things are misplaced.

Here is the lab and data sheet:

pulley-lab-rev-c2

pulley-lab-data-sheet1

I would love suggestions and ideas to improve this lab.  I’m still not thrilled with the overall lab, but it’s the best I’ve been able to do so far.