I teach from Holt Physics.  The book treats sig figs mostly okay.  When they provide numbers for problems, they are always precise.  Usually the numbers are in scientific notation, so you know where you stand with your given information.  The book does state that 1500 could be 2 or 3 or 4 significant figures because we don’t know about the two trailing zeroes.  I tell the students to err towards caution in those cases and treat that number as though there are 4 sig figs.  The book correctly states that the answers are rounded to the least significant number of figures.  You all know what I mean.

Here is where we part ways.  I teach my students to carry an extra place while doing calculations.  For example, if I’m dividing 35 by 62, my working answer is 0.565.  If this is my answer to the problem, I would round this to 0.57.  If I’m using this number in another calculation, I would use all three digits.  The textbook rounds this here along the way even when it is used later.  I’ve even seen problems where they have rounded more than once in the same problem.  (There is no way I can remember the actual problem right now.)   The results are often an error of about 10% difference between my answer key and my calculations.

While we are at this, I have a question I’m stuck on.  Suppose you read a meter stick and you get a reading of 8.65 cm.  That is three significant figures.  Now you move a little ways up the ruler and read 22.40 cm.  The accuracy of the ruler hasn’t changed, but I’m now working with 4 significant figure versus 3 before.  I wouldn’t round the second number, it is as accurate as the device, but the first number isn’t 8.600.  How do you account for this when you are dealing with the significant figures of a problem?

First was my LEGO version of the Hungry Hippo game.  The students were tasked with creating a robot that drives around gathering balls and marbles.  The robot that collects the most points worth of marbles and balls in 60 seconds wins the challenge.  The balls are the colored balls that are included in the robot kits.  The large balls are worth 5 points each, the marbles are worth 2 points.  Students had to come up with a strategy and then build to that strategy.  The best design drove around with a scoop on the front that shoveled the captured balls into a bin on top.  Many designs had rotating claws in front to direct the balls into a pen.

About a week into the challenge, students were tasked with doing a design review with another group.  They had to critique the other groups’ project and suggest ways to improve the design, then have the same done for their project.  All of the groups felt they got something out of the design review process.

The arena was our own Octagon I created out of 1×4′s.  Each side of the octagon was 24″ and the sides were held together with masking tape.  It was sturdy enough that the robots could bump into the walls and trigger a touch sensor.  The plan was to have the robots go head to head in the arena, but they all locked up so badly that each robot did individual one minute runs.

The latest challenge was a rope climb.  I first showed the kids a couple short videos on the space elevator and we had a short discussion on the cost benefits of such a system.  They were given a short week (4 days) to design a robot that could climb up a rope.  I hadn’t tried this before so I didn’t know what to expect.  I had a few robots climbing the rope within 30 minutes, so I had to up the ante.  Basically, they got a C if the robot climbed the rope.  If the climber carried a 0.5 kg weight up the rope, the group got a B.  If the robot managed to carry a full kilogram weight up the length of the rope, the students earned the A.  Only one group managed the A using an innovative design of tires and belts.

I’m going to challenge them to go back to the drawing board on this one and see who can carry the most weight up the rope.  After that, we are going to do Robot Wars in the Octagon.  The goal is to disable your opponent or remove them from the ring.  It should be fun.

Lame graphic, I know. Sorry.

As I mentioned in my 3-part update, my students absolutely love SBG in Calculus and have requested I move the system into my Physics classes as well.  However, after studying the problem at length, I have to take the tact that Frank took.  SBG as it is implemented in my Calculus isn’t a clean fit in Physics.

I’ve had to make some modifications, and I’m pretty sure I’m there will be modifications in the future.  Instead of solving two problems perfectly to achieve mastery, Physics students will have three, but they will be tiered.  Here’s how it’s going to work:

• Most concepts will have three levels of problems: C-level, B-level, and A-level.
• Students must get a C-level problem perfect to take a B-level quiz.  The B-level problem must be perfect to take the A-level quiz.
• If they get the C-level correct, they earned a 75% in that concept.  A correct B-level gives them 85%, and a correct A-level problem boosts the concept score to 100%.
• C-level problems are basic.  Everyone should be able to solve them.  B-level problems are a little more advanced, but everyone should be able to get these correct with practice.  A-level problems are challenging and most of the class will not get these unless they really put in the work.
• The 4 point grading system in still in effect, there is no partial credit.  This makes grading much quicker.  A 2 on a C-level is worth 60%, a 3 is worth 70%.  On the other levels, they only improve the score if they are perfect.

Quiz day will not have a standard group quiz.  I have lots of 1/2 page concept quizzes.  A student gets the quiz level for each concept based on what they have mastered.  Yes, this is a hell of a lot more work, but my classes are small.

Here is how I divided up the concept “Upwardly Launched Projectiles:”

• A C-level problem is a projectile launched and landing on the same level.  They are given an initial velocity and an angle.  They have to find the time in flight, max height, and range.
• A B-level problem involves different elevations for the launch or landing, or a building or mountain to hit or go over.
• An A-level problem requires more math, like simultaneous equations or the quadratic to solve for initial velocity.

Points for the concepts are going to vary based on the depth of the concept.  Projectiles will be worth 50 points while Relative Motion is only worth 30 points.  Some of the topics will only have two levels, a B-level and an A-level, simply because there isn’t enough difficulty to warrant three levels.  But those levels, like relative motion, will also not be worth as many points in the system.  I’m still keeping grades for  Homework (5 pts), Labs (25 pts), and the occasional WebAssign (around 15 pts).

We had our first quiz today and it went well.  A few of the better students got 4′s on the C-level problems.  I was able to grade about 15 full quizzes in under 15 minutes because of the 4-point system.  I was also able to be a real stickler on the significant figures because the kids have time to correct their mistakes and get it all right.

I’m incredibly optimistic about the change.  The students are a bit nervous, but they’ve heard so many good things from my calc kids that they know this is going to work to their advantage.  I know they will be doing a lot more work and keep at the lessons longer than they would under a normal grading system.  I’ll keep everyone apprised.

Right after soccer ended, kids started coming after school for concept quizzes.  I started throwing problems on paper, trying to get a pile of quizzes together, it was a mad-house at first.  Some days I would have 5 students all wanting different quizzes.  Each concept quiz consisted of two questions.  At least I kept a list of the problems I gave out.  It was chaos, I had to improve my methods.

I had been keeping the after-school quizzes in a pile.  One night I finally sat down at my computer and created two or three quizzes for each concept area.  I put a 31-day divider into a binder and put the quizzes in each section by concept number.  At work, I made several copies of each quiz and put them in the section behind the original.  Now when a student needs a quiz, I open the binder and pull out a quiz.  The front of the binder contains the weekly quizzes that cover from three to six concepts.  These are given sequentially every Friday.  Any of this material will be available to any teacher that requests it.  Feel free to borrow and improve, or just borrow – whatever works for you.

At first I kept their quizzes so they couldn’t share them with friends.  Once I got organized, I realized these were a valuable tool.  I created a folder for each concept and stored the quizzes in the folders.  This let me keep track of who took what quiz and what problems were giving the class trouble.

I soon realized I had to slow things down a bit.  Students would show and take another quiz after school, but not do any better on it.  I changed my method completely.  Now I make them explain the concept to me.  If they sound like they understand the concept, I’ll give them the quiz.  If they don’t, I insist on tutoring them on the concept before I’ll give them the quiz.  This has significantly increased their success rate.

Concepts

The first SBG concept was Symmetry, the second was Domain & Range.  I still have several students that have not mastered those one or both of the concepts.  If I hadn’t switched grading systems, those students would have done poorly on the quiz or test and moved on.  They might have worried about the concept for the midterm or final exam.  Some of my kids have been working to learn Symmetry and Domain & Range for six weeks now, and they won’t give up.  Yes, I’m sold on SBG!

When I started this, I was really concerned about dividing the course into concepts.  I was hoping to find a concept list online, but I didn’t.  The key is to look at the big picture – not everything needs to be its own separate concept.  For example, the Power Rule is part of the Product and Quotient Rule.  You can’t do a product or quotient derivative problem without knowing the Power Rule, so it is tested sufficiently.  The book is organized well, we use Larson’s AP Edition of Calculus of a Single Variable.  So far, my concept list is:

1. Symmetry
2. Domain & Range
3. Graphical Limits
4. Algebraic Limits
5. Continuity
6. Infinite Limits
7. Limit Process
8. Product & Quotient Rule
9. Chain Rule
10. Implicit Differentiation

I closed out the list for the first quarter at number 7.  As I write this, we are about to start the Chain Rule and we have almost two weeks left in the first quarter.  We are adding roughly one new concept per week, most quizzes have six concepts.  I probably won’t update this post as the year goes on, but if you email me, I’ll share whatever you need to get this working for you.

I’m extremely happy with the results.  The kids are happy and they are learning calculus, not just trying to get through the course.  I think I’ve made the course a little tougher knowing they can come back and take the time to learn all of it.  I asked them today what they liked and disliked about the new grading system.  I asked them for changes, anything at all.  They unanimously said the loved the new system and didn’t want to change anything.

Personally, I’m struggling with not grading on a normal curve.  My class average is too high, but they have learned the material, really, deeply, honestly, learned it.

Each problem gets one of four grades:

• 4 – The problem is done correctly, no errors
• 3 – The student understands the underlying concept but made at least one or more mistakes
• 2 – The student is starting to understand the concept, but clearly isn’t there yet
• 1 – No real understanding
• 0 – No attempt at a solution

Grading in the grade book is simple.  Students get the highest score achieved times ten.  If they do worse on a quiz, nothing happens to their grade.  When they get the first 4 on a concept, they get 40/50 in the grade book.  Get a second 4 and the 40 becomes a 50 and they are done with that concept.  The kids love to write “MASTERED” on a completed concept.

I’ve set up a spreadsheet (Gradebook – names are removed) in Excel to handle the grades.  Each student gets their own block.  When I enter a quiz grade, I change the header grade and change the color to  orange to remind me to change their grade in the school system.  Blue means the concept is complete.  Red numbers means the grade came from an after school quiz and not a weekly quiz.

The students use a Concept Checklist to keep track of where they are on each concept.  Every week or so I cut up my spreadsheet and hand out the pieces to make sure their scores agree with mine.  I plan to start a new spreadsheet each quarter since I can’t change the previous quarter’s grades.  So far, this is handling my grading requirements.

Next post – Setting up concepts and creating quizzes

The first quarter is almost done and I’m incredibly pleased with my conversion to Standards-Based Grading (SBG).  I’m glad I started with Calculus, the kids have been an understanding group and open to trying something new.

I began by setting up the scoring, each concept was worth 10 points.  The only other grade they have is a weekly WebAssign grade.  Those are usually worth between 15 and 25 points.  I found the WebAssign was too heavily weighted and the concepts didn’t have enough impact, so I did some analysis last week and seven weeks into the first quarter I changed the concepts to 50 points.  I printed grade reports and noticed that the point change lowered everybody’s score.  I expected an outcry, but it didn’t happen.

I explained that with three weeks to go in the first quarter, any new concepts will get entered into the second quarter.  Since I will not have the option of going back and changing their first quarter grade later in the year, I needed to give them enough time to master the early material.  What I explained to them is that their grade report showed the lowest possible grade for the quarter.  They all have three weeks to bring their grades up to an ‘A’ and they all can do just that.

Suddenly it clicked and the kids are coming in during their study hall and after school.  The rule is they can take a single concept quiz each day; plus we have a quiz every Friday in class.  At first they were dreading the quizzes, now that they understand that a quiz can only improve their grade, they love the quizzes (well, maybe not love – I do make them rather challenging).

The students are motivated to learn the material, they finally feel like they have control over their grades.  I know this is creating a positive learning environment.  All of my calculus students that have me for physics asked me to switch the grading system in physics.

Next post – The Grading System

I’m seeing errors much more than ten times that number.  I can’t seem to find a way to solve the problem.  We are using yellow RESET block, light green MOVE blocks, and orange rotational WAIT blocks.  We have a spot carefully marked on the floor for the start and way points.  Starting at the same spot may have the robot as much as an inch off within about 10 rotations.  The total motor error should be about 0.17 inches.  I can’t determine if it’s a problem in NXT-G or the motors.

I’ve searched the NXT books, blogs, web sites, and books, and I can’t find any references to the inaccuracy issues.  Has anyone else seen these problems?  How do I fix this?

Because of DropBox, I no longer have my lesson plans on a USB that I have to carry around.  The files reside in my DropBox folder, and more importantly, there is only one version of it and it is always the most updated copy.

There isn’t much of a downside to the app.  People don’t have to be members or download the app to be able to use your shared folder.  You start with 2.0 GB of space and earn 250 MB each time someone you invite installs the app on their computer, up to a total of 8GB.  People can access the folder without downloading the app, but if they don’t download the app, you don’t get the bump in storage.  You can also increase storage up to 50GB for $100 a year.  I’d probably consider subscribing if it was about half that, I just don’t need 50 GB right now.

If you want an account, do me a small favor and let me send you an invite.   Click on my Contact Me link.  Doing so will get you an extra 250MB, and do the same for me.  Then you can share it with your friends and coworkers if you love it.  I love it.

The second app on my list for today is called Evernote.  Evernote took some figuring out for me, but once I saw the light, I’m a convert.

Here’s how you use Evernote – you upload photos, pdf’s, and random stuff.  You write lists, send web pages, and scan business cards.  All that crap that you need but you don’t know what to do with it, it goes in there.  Here’s the golden nugget of Evernote – anything in there becomes searchable.  So that business card, just take a picture and upload.  Now you can search for that person or company or title.  Instead of keeping the instruction manual for all those electronics gizmos, upload the manual.  If you ever actually need it, you can search the manual through Evernote.

Just like DropBox, the app is on everything.  You can install an add-on to Firefox (and probably other browsers) to directly upload to Evernote.  Just highlight, right-click and at the bottom of the menu is “Add to Evernote.”  The limit here is you can upload only 60MB per month (each month), which I’m finding is an enormous amount of stuff.  I saw something at Home Depot that I wanted to remember, so I took a picture and sent it to Evernote and added notes later.  I’m sure there are other ways of using it, like they have tags you can attach to everything and notebooks for organizing, but I’m using it as a warehouse for manuals, business cards, recipes, and other things that just don’t fit anywhere else.

You can go premium with them for just $5 a month and they have educational discounts as well.  Most of the negative comments were about not being able to share the data.  I don’t want to share this stuff, it’s my junk drawer and attic all in one.

The goal here is STEM, that’s what opened the door for the robot invasion in the first place.  Clearly missing from our program these days is what we called in the old days, ‘drafting.’  Drafting isn’t done on a board with a T-square anymore, but you all know that.  Today, 3D mechanical Computer Aided Design (CAD) is available for free from Google (Sketch-up), and from a number of companies who cater to the high-end.  I actually know this industry well, I spent 25 years in the CAD/CAM/CAE industry (M for manufacturing, E for Engineering, meaning simulation).

So with some guidance from some friends at Drexel University, and a little research on my own, I decide to go with SolidWorks software.  All of the vendors have aggressively priced programs for the educational market, I think we are paying just $1000 for a 10-seat license.  What makes this software connect to the students is what we spit out of it.  The school invested in a 3D printer, specifically uPrint Plus from Dimension.

If you have never seen one of these, think Star Trek Replicator.  The replicator creates parts from ABS+ plastic directly from the output of the 3D CAD.  How better to teach engineering principles than to give the students a design challenge, have them work through designs and then fabricate it in the printer.  Here is a great video from a customer talking about how they use a 3D printer in their engineering design work.

My new printer is due here any day and I’m pumped up.  Yep, geek boy has a new toy.  Tea, Earl Grey, Hot!

Last year, one of my students came into class second or third period and said how much he loves coming to my room.  I thought it was odd because he wasn’t a particularly enthusiastic physics student.  Then he said he loves the way my room smells.

Every morning I make a pot of coffee, often flavored with vanilla or hazelnut.  I never thought about the impact something like a nice smell has on making a student feel relaxed.  I’m still making coffee every morning, but this year I picked up a bunch of scented tea lights from IKEA.  These things smell so good, my son and I bought a pack of every flavor they offered.

I have heard stories of real estate agents putting a drop of vanilla on a warm oven at an open house to make the home subconsciously remind the potential buyers of home-made freshly baked cookies.  Maybe getting another one of their senses involved improves learning.

I won’t lie, it took me several hours of reading to get the gist of it.  Frank refers to a post by Dan Meyers.  Follow that link and read through the comments.  Others readers had many of the same questions I had; reading the questions and Dan’s responses pulled it all together for me.

I haven’t got it all worked out just yet, but I plan on implementing this in my honors Calculus class.  My administration backs me on all of my adventures and didn’t bat an eye at it, “sure, go ahead.”  After all, this one isn’t going to cost them thousands of dollars (I’ll fill you in later). I’m going to steal everything I can from Frank while I work out the methodology and the glitches in a small and forgiving class, then move it to my physics class the following year.

Here is my understanding of the concept in a nutshell:  The course is broken down into approximately 40 key concepts.  Students are assessed on those concepts. Once they get two questions perfect on that concept, they no longer need to answer those questions on later quizzes because they have already mastered the concept.  They can keep retaking quizzes on the concept until they get two of them perfect.  In the mean time, class moves on.  (We hit the wall a few times in calculus last year where we didn’t move off a section for over a week because about half of the students didn’t master the concept.)  Students track their own successes and know what they need to practice and get tutoring on.  They can get a 100% in the class, but my guess is you still end up with a normal distribution curve because many of them will feel that a 60% or an 80% on some of the concepts is acceptable.  However, if they choose to work hard and improve their grade, they can keep relearning and quizzing on the material until they master it.

Frank and Dan both have their own grading system.  I would read their posts and decide what makes sense for you.  I’m just getting started on mine, but my guess is I’ll steal one of theirs and tinker later.

It’s going to be a bit more work the first time around and a lot more time tutoring and retesting after school, but my goal is for the students to master the material.  I want them to take the Calculus AP exam and knock it out of the park.  This seems like the right approach.  I’ve ordered the three books Frank has recommended, you can find them very reasonably priced on half.com.  I think I paid about $25 for all three including shipping.

I’d be really interested to know if any of you have used similar systems and how they have worked for you.  My gut tells me this is the right way to go.  I nervous at the increased workload (again).

Okay, I’m done being silly.  I did really get this, although I only found out because I was on the site and saw I was one of the listed blogs.

So no, there was no cash award, no gold statue, not even an email telling me about it.  And as the new school year approaches, the hit count is heading towards half a million.  That just blows my mind.

Do click on the badge, there is a pile of great teacher blogs in the list.

My final exam next year will…

• begin with a multiple choice section on basic concepts & terminology
• have lots of basic problems with multiple choice answers
• have a very small written portion – I’m keeping the Road Runner cartoon, it’s my favorite part
• be graded in under two hours

One of the questions this year asked the students to discuss three principles used in their Rube Goldberg project and explain the application of the principle.  I was looking for concepts like inertia, momentum, kinetic energy, and force.  I just graded a paper where the principles listed were ball, dog, and ball.

If it’s multiple choice, I won’t have to learn that after a full year of physics, one of my students thinks “dog” is a physics concept.  I just wish it was a joke and not the truth.

I think many of us teaching a measurement lab have the same problem.  The students don’t understand measuring or estimating.  Given an object, they will always have the same answer, regardless of whether it is right or wrong.  So I am hereby creating a lab using fictitious units.  We will use a willing volunteer from each lab group and declare his or her height to be one “Smith” or “Jones” or whatever his or her name happens to be.  We will then do some exercises to estimate fractional distances.  I think I will give them string and make them use a meter stick to get a measurement of the “Smith.”  They will need to figure out how to divide the string into tenths and hundredths and then estimate to the thousandths.  I won’t tell them how to do it, they are going to need to figure it out on their own.

My hope is that they will come up with their own method and get a better understanding of estimation.  The beauty of an inquiry lab is how little detail they get from me.  Personally, I’m excited about this one.  I think we are looking at a first or second day of school lab here.

Here is my first pass at the lab handout.  Lab 00 – Measurement Lab

You can read about Oliver Smoot and hear an NPR interview here.

I wanted to put lead shot in the bottles, but I didn’t have any.  I was going to purchase fishing weights, but for what they cost I decided to just use pennies.  They are mostly copper, fairly dense, and I can fill a bottle for about 20 cents.  It turned out to be cheaper to use money as a weight than to spend money to buy anything else.  In some of the bottles I put odd screws and other metal bits to increase the density.  I made sure none of the masses were at even values, and they are all different values.  In other words, the mass of one bottle was 87.2 grams, not 80.0 grams or 85.0 grams.  For some reason, my students believe all answers should be whole numbers.  Of course I don’t believe that.  I numbered the masses #1-#12, weighed them on my gram scale, and recorded their mass on a note card and stored it in my desk drawer.  During the lab, I refused to tell them the values of their unknown masses, and my gram scale was locked up, but I did tell them their answers should be in the range of 75 to 120 grams.  I did find the unknown weights would work better if they were more in the range of 150 g.  I’ll have to see what lead shot costs, maybe a bag of it is in my future.

During the lab, I instructed the students to make note in their lab notebook of which unknown mass they used during the lab.  I explained that each mass was different and they needed to stick with the same one each day.  Despite the explanation, about half the groups didn’t make note of which unknown mass they used.  Some of them just said it was white.  Well, at least we have colors down.

As I mentioned before, I’m on the fence with extra credit.  I’m now totally convinced that anything purchased for extra credit is just plain wrong.  I don’t think there is a gray area here.  No pay-for-points.  I’ll play the benefit to society game because the results outweigh the costs.  I will provide extra credit when it works to my advantage.  If the students correctly answer their WebAssign problems 48 hours before the due date of 8am Monday morning, there is a 10% bonus.  For a very few extra points, I get far fewer Sunday night emails.  Instead, they want the extra credit, so they bring in the problem during school and ask for guidance.  The result is they are looking at the work early in the week rather than waiting until the last minute.  Am I tricking them into better study habits?  I’ll take that.

I do like the idea that extra credit is for work above and beyond the norm.  This brings me back to where I am right now, with a lot of kids in bad shape as the end of the quarter nears.  My fear is that the normal grade distribution will be badly shifted by an extra credit assignment.  I am a big fan of a normal curve, with an average at a C+.  I give challenging tests and curve up to make the class average about 77%.  The A’s earn their A’s, as do the F’s.

So what is an appropriate extra credit assignment?  Here are a few ideas I’m thinking about:

• A 2000 word research paper on a Nobel prize winner in physics and the impact of the discovery on our every day life.
• A video that teaches a physics concept, done so that I can use it in class.  It should be scripted, edited, and several minutes long.
• For less points – Creation or redesign of a lab for use in future classes.

None of these can be group projects; they must all be individual efforts.  Points awarded for this level of effort should be valued at about 5% of the total quarterly points.

I’m right at the point where I need to assign these if I’m going to allow extra credit.  The quarter ends in about 12 days.  I could use some feedback.

I’m not a fan of extra credit.  Here is how I lay out my thoughts on the matter to my students:

• If you don’t turn in your work when it is due, extra credit is not for you.  (This will be the one and only rhyme in this post, I promise.)
• I curve the grades.  I make the tests and quizzes challenging, then I curve the average up to a C+.
• You want to do well in my class, do your homework, come in for tutoring, pay attention in class, take notes, study for the tests and quizzes.  Do your homework!
• My course is designed so that honestly attempting homework banks enough points to overcome poor test scores.  Did I mention, “Do your homework?”

There are some students that do all their work, they really try, but their math foundation is shaky and/or they don’t test well.  If you work hard but fail tests, I tend to secretly award point at the end of the quarter for coming in for tutoring.  Most teachers won’t fail a student that really, sincerely tries, but doesn’t succeed.

Now, about that extra credit.  Generally I don’t like it, but sometimes it’s my idea, sometimes it’s a request from another teacher or administration, like…

Toys for Tots:  Bring in a toy, help another child and you help yourself.  This one, the ends clearly justifies the means.

Support school spirit:  Attend a basketball game and support our team.  It was only 5 points, the value of a homework, so sure.  After all, I am the boys soccer coach.  Go CHARGERS!

Warning – slippery slope, proceed with caution!

Students that volunteered to help other students with their science fair projects (as research subjects) and were picked were given points.  Many applied, but few were chosen.  So if you were picked, you got 20 extra credit points.  That made a big difference for a few lucky people.  Extra credit is now a lottery.  Buy your tickets at the door.

So how about these:

• Points for bringing in a (usable) box of tissues for the classroom?
• Buying a fish for the fish tank?
• Buying batteries for the robots?
• Buying white board markers for the classroom?

So now it’s all about the Benjamins.  (For you international readers, those are $100 bills.)

Where does it end?  I mean, I’d really like a boat.

This all started because the school purchases Expo markers for the white boards.  I stopped using them, they don’t erase well.  I’ve been purchasing Quartet fine tip markers from Staples when they go on sale for $1 for five.  Yeah, the sale just ended, sorry.  I like these, they don’t leave a residue when you erase the board, so I never have to spray the white boards anymore.  I thought about letting anyone who wanted extra credit go out and purchase two packages for $2 (the store limit), but my conscience got in the way.

See where this takes us?  I mean, sure I really wanted them to buy me more markers, but the fate of the free world is in my hands here.

But seriously, if only for a moment, do we assign extra credit projects or purchases for students that don’t do their work when it is assigned?  How about students caught cheating?  Did I mention that roughly 30% of our students qualify for free lunch.

An engineering degree, a Master’s degree, twenty years of corporate sales and eight years of teaching just hasn’t prepared me for this decision.

I really do want a boat, though.

In our recent lab, the kids had to measure the height of the toy popper.  The poppers I have are 3/4″ and 1.5″ in diameter.  When students measure these using a mm scale, I routinely get heights of 0.01 meters and 0.02 meters.  The next step they calculate the acceleration and give me results to four significant figures.  I need to get a few stamps made up for grading.  One will say SIG FIGs, another will say SHOW UR WORK, and a third will say FORMULAS? since the kids seem to think I know what formula they are planning on misusing and abusing.  Maybe I can boil all of my grading down to a series of stamps.

The problem here is that I tell them repeatedly to measure to at least two sig-figs.  You can comfortably measure the popper to 10.0 +/- .5 mm on the scale.  I have to take most of the blame here, since I don’t do enough in the beginning of the year teaching them to measure.  I need to put together a lab that teaches them how to measure, weigh, and calculate.  Then I need to hold them to those standards for the entire year.  I don’t understand how students get to the 11th and 12th grade and can’t successfully use a ruler.

I often wish I could go back in time and see if I was as oblivious in 12th grade.  Was I this lost?  Every time we use the meter stick I instruct them that we only use the metric system in our class, and still a few will measure in inches.  (I’ve been saying for 5 years that I will spray paint over the inch scale soon.)  We did the Egg Crash Lab yesterday (big success), and more than a few of them couldn’t find “half a meter” on the meter stick.  If this was the first time they’ve used a meter stick, I would understand, but we use them pretty much every other week and we are six months into the course.  Maybe I’m just expecting too much.

What is interesting is as I’m becoming more aware of the problems with sig-fig abuses, I’m finding errors in other places.  The software that maintains our student records keeps the grades to 2 decimal places.  (This is essentially 4 sig-figs, although you can technically have a 100.00 grade.)  The system rounds the grade to a whole number for the report card, but it also rounds them before calculating a semester and final grade.  It should be averaging the entire grade, then rounding.  In addition, the system stores the grade point average to 4 decimal places which is essentially 6 sig-figs.  I noticed the problem when I recently calculated semester grades and many were off by a point from the system calculated grades.  To the student that is struggling to learn physics, that one point can mean a B instead of an A, or an F instead of a D.

To quote Zack from The Big Bang Theory, “that’s the beauty of science, there’s no one right answer.”  Bazinga!

Anyway, as I had mentioned in earlier posts on momentum, I wanted to do the egg drop competition, but I’m in a one-story building.  This year we are doing the “Egg Crash” competition.  The basic concept is that teams get 10 sheets of computer paper, 1 meter of masking tape, a pair of scissors, and 20 minutes to construct a free-standing object to safely catch the egg.  They drop their own egg from a height starting at 0.5 meters above the top of their structure.  The egg is inspected before and after each drop, the higher they go, the more points they win.  The surviving eggs are dropped from 0.5 meters higher each round until they all finally break.

I usually allot 25 points for a lab, I will probably go 50 for this one.  Deb said she does 100 points, but that’s a test grade and I don’t think a one-day lab should be worth that much.  I’m still working out the scoring, but I think I will assign a grade to each height.  If they fail at 0.5 m above their structure, they get 30/50, but they also get a single start-over with a new egg.  Each 0.5 m interval earns 5 more points.  That means surviving 2.0 m earns 50/50.  I’m willing to give 5 or 10 extra credit points if they can survive a drop from 2.5 or 3.o meters over the top.  I was going to do direct competition for the points, but what if everyone fails at 1.0 meters?  With my grading system, they all get 70% since nobody really earned the A or B.

I handed out the Egg Crash Description and Rules on the day we started learning about Momentum.  I told them it will be about a week before we do the competition; I wanted them thinking about the problem and their design as we learn about momentum and impulse.  This week I will show a great video called “Car Crash Tech.”  The video discusses the state of the art auto safety systems and the effects of air bags and other innovations.

I’m hoping for some creative solutions from the kids.  Maybe I’ll have a picture or two to post here in a couple of weeks.

• Many kids don’t do their homework
• Many kids copy their homework from the kid that does his/her homework
• The kid that does his/her homework tends to do well in the class
• The kid that copies his/her homework tends to not do well in class

WebAssign allows me to give them an assignment they can’t copy since each student gets a different set of numbers in the problem.  Oh sure, some still don’t do their homework, but the zero in the grade book is indisputable when we can pull up the WebAssign grade for Mom and Dad.  The kids have a week to do an online assignment.  No, the dog did not eat your computer.  No, you had a week to do it.  No, I don’t take late work.

My homework template was set up to allow up to five entries on an assignment.  At first, there was no penalty for getting it wrong.  I did an experiment in my calculus class and penalized them 10% for each incorrect attempt after the first two attempts.  The kids really resented that.  I think they felt like they were willing to keep trying, they didn’t want to be penalized for not quitting.  Lesson learned, next experiment.

Recently I tried a new approach (ah, the scientific method at work).  I started giving 10%-20% extra credit for completing the assignment 48 hours before it is due.  With the assignment due Mondays at 8am (the start of school), I was getting a bunch of  “help me” emails on Sunday evening.  The extra credit was an attempt to reduce these emails.  What I found is that more of the students were completing the work and doing it ahead of time.  Yahoo!  They will do their work if they feel they can boost their grade with extra credit.  The reality is most of them don’t earn the extra credit, but they get the points for doing their work, and these online assignments are equivalent to a quiz grade every week.

But wait, this gets even better (I’m smiling as I write this).  The kids think they outsmarted me.  Ready for this … they are getting together to work on the problems.  Oh, I don’t know, call it … a study group.  AAAHHH!!

Original Tissue Paper Hot Air Balloon Post

The original plans make a balloon that is 60 inches high.  That is perfect for the classroom, it takes three pieces of tissue paper per panel and you need six panels.  You will find I went big on this one and made a 90 inch version for myself.  It is rather unwieldy and difficult to handle, but bigger balloon means bigger lift.  At this point, I can put one of these 60″ balloon together in about an hour, where it takes the kids at least 2 hours.

One of the challenges we ran into was finding the aluminum wire we used to keep the mouth open.  You want this for two important reasons; first, to add ballast; but more importantly, without it, the kids can’t catch the balloons on their heads.  I found the wire at Dick Blick, an art supply store.  They list it under sculpture wire, we use the 14 gauge wire.  It costs $16 for a 350 foot spool.  Each balloon uses about 3 feet.  That’s a lot of hot air balloons.

When it is too windy outside, we tend to launch these in the gym.  I have two heat sources.  The indoor one is a heat gun I purchased from Harbor Freight on sale for $10.  It works great, I make sure I handle it so nobody gets burned.  The outside source is a plumbers propane torch.  Nobody handles that but me, I don’t need to write up any (more) accident reports.  If you are using the torch, make sure the kids keep the balloon opened up, if you aren’t careful you can catch the balloon on fire.  Oops, only did that once, very cool though.  If you do that, light it from the bottom, it goes up into the air and disintegrates … poof.  Bad science teacher.

Some day I may make one of those cool chimney launchers, but then I’ll have to store it in my room.  It’s already looking like Sanford and Sons in my classroom, I don’t know how much more junk I can store.

http://www.walter-fendt.de/ph14e/

There are some really useful tools here for demonstrating mechanics to your students.  Best of all, he has a download button, you can just put them all on your computer and not worry about his link changing.  I haven’t been able to make the downloaded applets work, if someone can post some help, it would be appreciated.  I tried just clicking on them, they open up Firefox, but they all seem to fail.

If you have access to computers in your classroom, you can design lab experiments where the students input conditions into these applets and read the results from the screen.  Not as much fun as hands-on, but a lot better than lecture.  If you do create an applet lab, please forward it to me, I’d love to attach it to this post.

I decided to be only somewhat helpful.  At the start of day 2, I told them the initial velocity should be in the range of 5 m/s.  I told them I would not answer questions about their numbers if the formulas were not there and units were not shown.  I generally only told them they were either on the right track or wrong, nothing more.  Most of them had a tough time making the leap to the distance in part 2 was how far the inverted popper moved from rest to the calculated initial velocity.  Once they got that, they were well on their way to solving the problem.

Force v. Time Function for Toy Popper

I did an interesting experiment while they worked.  I set up a LabQuest to sample at 1 ms intervals.  I build a tiny tray from cardboard and string and attached it to the force sensor.  I set the meter to trigger at a force greater than 2.5 N, zeroed the sensor, and let it rip.  It showed a nice impulse function that took 23 ms and a peak force of close to 7 N.

I could use some help with my interpretation of the graph.  I believe the integral of the Force v. Time curve gives me the impulse (the LabQuest gave me a value of 47 N*ms).  If I divide that value by the mass of the popper (9.1 g), I get a delta v of 5.16 m/s.  This is in agreement with the numbers the kids got in the experiment.

Now if I divide the delta v by the time, I should have the acceleration.  The LabQuest samples every millisecond and there are 23 points, so I think the time is either 22 ms or 23 ms.  The acceleration works out to be 235 m/s^2.  Doing this, I only get a force of 2.1 N, but the graph shows close to 7 N.  The students calculated forces in the 6-7 N range.  I think the discrepancy has to do with using the integral (which should be more accurate) and getting a peak force compared to an average force.  Can someone either confirm this or correct it for me please?

We just finished Newton’s Laws before break, what better way to refresh their memory than making them think.  I got this lab from the NSTA regional conference in Baltimore, it is called “Inquiry in a Box” and presented by Deborah Roudebush.  I put the instructions into a format my students are more familiar with and I expect they will need two days to get their arms around the whole thing.  What is very different about this lab (compliments to Deborah) is that the students are given only the problem to solve, some minimal tools, and no instructions.  They need to figure it all out on their own.  It could be a disaster, I fully expect a lot of whining.

The basic idea is that the half ball Party Popper shown above is a cool little science experiment.  Giving them only a ruler and access to a gram scale, they need to figure out how to determine the velocity, time, and force exerted by the popping event.  At the conference, we were put into groups of four and set about solving the problems.  It didn’t take us too long, but there were some very good discussions on when the time and acceleration actually occurs.  There will be no answers posted here, some of my students know about this site.  If you need some help, email me.

Here is the lab handout:  Popper Lab Handout

Now, you would think these little poppers are easy to come by…  good luck!  I went to many toy stores and party stores and found none.  I ended up online at Oriental Trading Company.  Their 1.5″ poppers are great, their 0.75″ are going back, they don’t work at all.  I found another place selling them; Century Novelty.  I’m ordering 1″ poppers from them.  The key here is you have to plan ahead for this lab, you can’t run out to the store the day before and find them easily.  I won’t have the 1″ poppers in time for this year, but next year I plan for them to analyze different size poppers and compare the results.