The topic of monopolies and anti-competitive practices arose on a previous thread. In that context, I brought up the thorny issues of non-competes, in particular Jimmy John’s now rather infamous non-compete clause intended to prevent low wage fast food workers from taking jobs at other sandwich joints. (See Illinois case and NY case). (Turns out this is only one of the non-compete type clauses Jimmy John’s has been sued for. See the non-poaching clause.)

Anyway, since I find quite a few tutoring gigs through online “platforms” as they are called, I now read contracts between platforms and potential contractors from time to time. During a forum discussion of platforms, one visitor told other tutors about a “Frog Tutoring”, she thought we should all find beneficial to add to your stable of platforms. (Contracting with several companies can be sort of like working for Lift and Uber.)

Naturally, I trotted over to Frog to check them out. Wanting more information, like, how much they might pay a tutor, I entered information and filled out a brief form.

Filling out this form did not seem to involve agreeing to anything much. However, it lead me to a dynamic web page with directions on how submit an application to become a tutor. That page required me to sign a contract before learning things like how much I might be paid, whether Frog would actually consider me qualified or other pesky details.

Of course I read rather than reflexively clicking accept. Not only did I find their contract uninviting, I was sufficiently amazed by the provisions that I clicked “save as” on my browser to keep the contract for future reference. I think you will be amazed too!

My amazement is principally related to the “non-compete” and “confidentiality” sections. The contract includes the line “DATED this the 12th day of December, 2018, in Tarrant County, Texas, where the obligations contained in this agreement are performable. ” Their copyright clause indicates “© 2009 FrogTutoring. All Rights Reserved”.

As shown in the screenshot below, the instructions began with two steps, followed by a notice that “You need to accept the Terms Contract before you can use the Site”.

Let’s now discuss the contract. I have no issues through Articles I -IV. Let’s look at Article V:

ARTICLE V.
CONFIDENTIAL INFORMATION; COVENANT NOT TO COMPETE

5.01. The Company possesses secret and confidential information and equipment, techniques, processes, procedures, technical data and information, and customer and client lists used or intended for utilization in its operations of which Contractor has obtained or may obtain knowledge and Company would suffer serious harm if this confidential information were disclosed or if Contractor used this information to compete against Company. Accordingly, Contractor hereby agrees that simultaneously with the execution of this Contract, he or she shall execute and deliver to Company and during the term of this Agreement and thereafter as provided therein, abide by the terms of a “Confidentiality Agreement and Covenant Not to Compete”,a copy of which is attached to this Contract as Exhibit A.

So basically: non-compete associated with this contract is sufficiently long as to require an entire additional exhibit!

Before moving on to the document, i.e. Exhibit A, let us consider the claims about “secret and confidential […]”, which does, indeed look a bit boilerplate. After all, in principle all companies have some confidential information that do not wish to have disclosed. Having said that: it is pretty unlikely any individual tutor will be given access to anything truly confidential. What a tutor is likely to have access to is the name and address of individual clients who they subcontract to me to tutor. This is very similar to an Uber driver: The Uber driver does end up briefly meeting and talking to the passengers in their car. They might learn something about the route Uber prefers use to drive from point A to B. Customers can also learn this by using an Uber car to go from point A to point B.

If Frog’s operation does give tutors access to lots of truly confidential information, it’s a slip-shod company that is probably leaking information willi-nilly. Presumably, when operating they do not leak all sorts of confidential information to contractors.

Now for Exhibit A!

CONFIDENTIALITY AGREEMENT AND COVENANT NOT TO COMPETE

The undersigned (hereafter called “Contractor”) has entered into an Independent Contractor Agreement for Academic Consulting Services (the “Contractor Agreement”) with Frog Tutoring, LLC, a Texas Limited Liability Company having a principal place of business in Tarrant County, Texas (hereafter called the “Company”), which is engaged in the business of tutoring services.

By signing this agreement, Contractor acknowledges his or her understanding of the following:

• The Company has information generally not known outside the Company called “confidential information”. All companies must conduct their business through their employees and independent contractors, and consequently many employees and independent contractors must have access to confidential information. At times, the Contractor himself or herself may generate confidential information as a part of his or her services rendered to Company.
• The phrase “confidential information” as used in this agreement comprises any technical, economic, financial, marketing, computer program, regardless of the medium on which they are stored or written, computer software, computer data, computer source and object programs or codes, job operating control language procedures, data entry utility programs, sorts and miscellaneous utilities, disk record layouts, flow charts, data entry input forms, operation and installation instructions, report samples, data files, printouts, or other information which is not common knowledge among competitors or other companies who might like to possess such confidential information or might find it useful. Some examples include prospect lists, customer lists, items in research or development, products, inventions, innovations, designs, ideas, trade secrets, proprietary information, scientific studies or analyses, details of training methods, new products or new uses for old products, merchandising and accounting, long-range planning, financial plans and results, marketing plans, sales and profit figures, computer programs and operating manuals, computer source codes, etc. This list is merely illustrative and the confidential information covered by this agreement is not limited to such illustrations.
• The Company’s confidential information represents the most important, valuable, and unique aspect of Company’s business, and it would be seriously damaged if Contractor breached the position of confidential trust Company has placed in him or her by disclosing such confidential information to others or by departing and taking with him or her the aforesaid unique information compiled over a period of time for the purpose of the Contractor competing against the Company or disclosing such information to the Company’s competitors, now existing or hereafter formed.

It’s certainly true that companies conduct business through employees and contractors. Some of these people need access to some confidential information. But often, the majority of employees need access to very, little to no “confidential” information. I suggest people look at the exhaustive list of potential confidential information. I would suggest that the chance that a tutor would have access to “scientific studies or analyses”, “accounting methods” or “long range planning” is pretty dang slim. It’s probably about as likely as the notion that a Jimmy John’s sandwich delivery guy would have access to these things.

Also: there are some legal problems with contractors requiring independent contractors to undergo large amounts of in house training, as such company specific training and requirements to do things in company specific ways tends to make someone an “employee” rather than an “independent contractor”.

So, while Jimmy John’s might have been able to make a valid claim they provide and require company specific training in skills like “how to wrap sandwiches the Jimmy John’s way”, similar company specific training tends to be less valid for people who work as independent contractors.

But, perhaps all that generality would make sense if the company was about to explain only that you agree to not leak the information. They do require the contractor to pledge that. But they require more. Here goes:

2. Covenants Not to Compete. Contractor agrees as follows:

• Contractor has and will require special training, enhancement of skills and knowledge at Company’s expense, which could be subsequently used to the detriment of Company, Contractor expressly covenants that for a period of five (5) years following the termination of this agreement, or his employment, for any reason, she will not directly or indirectly own, manage, operate or be connected with the ownership, management, operation or control of, consult with, or be an employee for any business offering tutoring services to customers or clients of the Company within the metropolitan area specified in the Contractor Agreement and within five (5) miles of such metropolitan area.

Note, in my case, the “metropolitan area” was “Naperville”. Since I tutor in this area, I already “own, manage and operate” my own tutoring service to customers. Moreover, every single contractor who enters into this agreement currently does this– and the language of the contract appears to permit them to do so while the contract is in place. (In fact, it must. Otherwise, the “contractors” would be “employees”.)

But, evidently, according to this contract, following termination of the agreement, I would be barred from being involved in tutoring services near “Naperville” for 5 years. At least that’s the way it reads to me.

This is justified by a lot of quite hypothetical things, but in reality, I would be binding myself to agree to stop tutoring local students pretty much in the hope that Frog Tutoring would locate students for me, subcontract the job to me, and have me bill the students through them.

In my mind, the above was enough to make me decide not to accept this agreement. It was also enough to make me keep the html to refer back to later.

But there are actually some other clauses I found remarkable. Among other things, had I signed the contract, I would not be allowed to discuss the contract itself and specifically my pay with anyone, especially not other tutors!

3. Non-Disclosure of Terms. Ancillary to the agreement for confidentiality, Contractor agrees to keep all terms of the Contractor Agreement and this agreement, including but not limited to information about Contractor’s compensation, and will not disclose any such information to any third party, specifically including any other independent contractors in a similar relationship with the Company, and any customers or clients of Company.

In case you are wondering if the company means to this contract to bind the tutor: they seem to. In fact, the offer a consideration to make this contract hold. Preceding all the non-compete disclosure requirements, the contract states:

Accordingly, in consideration of ONE DOLLAR ($1.00) paid to Contractor by Company, the receipt and sufficiency of which are hereby acknowledged, Contractor agrees as follows (which will constitute an agreement ancillary to the Contractor Agreement with Company):

and ends with

DATED this the 12th day of December, 2018, in Tarrant County, Texas, where the obligations contained in this agreement are performable.

So, it appears the contract as offered would have me enter a deal where (as far as I can tell), Frog would (perhaps) help me find additional local students to tutor. How much they would charge the students or pay me is unstated; evidently I’d learn that after signing and getting my $1 to make this binding. ( If I ended the contract immediately, it appears I would have given up my right to tutor students locally for 5 years.

What a great negotiating position to begin discussing pay!

Ok… maybe there is some aspect of legalese that only makes it seem to be saying this. Maybe Frog wouldn’t try to hold me to the “5 year non-compete” clause. Maybe, if I took them to court, a Texas judge would throw this out. (Any specialists in TX law out there?) Maybe all sorts of things would happen.

Having said that: I think this contract is much, much to risky for anyone to sign. The exception would be someone who had no intention of tutoring in the Naperville area, ever!

We need a new thread.

For your enjoyment, I’ve put up conversation initiated by a complete stranger on twitter. Read from the bottom up. Either someone is an idiot or someone hacked someone’s Twitter and is setting her up. But…oy.

FWIW: I’m curious to wonder just how much she would pay for this service but not curious enough to ask and give her the impression I might do it. I also have no idea how one provides these answers surreptitiously. Is it in class with a cell phone? Online with screen shots? Once again: not interested enough to be involved in the “research” to find out!

Open thread.

I’ve subscribed to the AP Students sub-reddit, principally to read what questions students studying for physics have, and to learn what resources they find helpful. This question caught my eye:

I know it’s probably much easier because when taking their diagnostic tests I ended up getting 30/35 on both of them, when I would think that I would get much less. Can someone who has taken the mechanics exam tell me how much it differs in difficulty?

This motivated me to go have a look at the Varsity Tutors diagnostic tests.

I headed off with the intention of evaluating so I could give my opinion arriving here. I wanted to evaluate the questions in a time efficient way. Given the set up, you are required to answer a question to move on, So I read questions, diagnosed them when I saw questions that struck me as odd, I took a screenshot, superimposed the url on the question. Then I then clicked answers at random and submitted so I could see the next question. I looked at 35 questions.

Here’s a question that caught my eye:

Am I hearing “But … !!!!?????!!!!!” If you are asking that: double plus good for you! If you picked 6N…. uhhmmm… no. If you picked 4N… well, we’ll talk about that in a minute.

Varsity Tutors claims the answer is 6N. Their explanation is shown to the right. Uhmm…

Perhaps your wondering why I’m writing “Uhmm”? Let’s look at this three ways.

1. Assume the book “held” and “kept” from sliding down the wall– as stated. Perhaps I am mistaken, but I take this wording to mean the force of friction is sufficient to keep the book motionless. Given the problem statement it would appear the frictional force and the force of gravity are the only vertical forces. So if the force of friction keeps the book from sliding down, the friction force must balance the book’s weight.
    

   Assuming this is all happening on earth: F_friction = m g ~ 1 kg * 10 m/s² = 10 N. That’s Newton’s first law. If the book is not accelerating, forces must balance. So this should always the right answer. (BTW: this is an important thing for students to know and the AP Physics C often have questions involving static friction and Newton’s law. Newton’s law always trumps F_s = μ_s F_N, because, among other things F_s ≤ μ_s F_N. That the inequality appears in that relation is considered a very important point for a student to understand.)

2. Now, lets suppose we ignore the fact the question tells us the friction force keeps the book from sliding and consider the possibility it is slding. In that case, we use the coefficient of kinetic friction which is 0.2, and F_friction= 0.2 * 20 N = 4 N. Given our previous answer we would also conclude that if the book is sliding, the book must be accelerating downward because this force is less than the downward force due to gravity.
3. If we use the solution Varsity Tutors gives– which is the correct value for the maximum possible force due to fiction, we get 6N. Ok. That’s what Varsity Tutors claims.
    

   But now ask yourself this: Is an upward force of 6K sufficient to “keep[[.]] the 1kg book from sliding”?
    
   Nope. At least not if this is taking place on earth because 6N is less than the 10N. So we should conclude that the force of static friction is insufficient to prevent the book from sliding down the wall. Unless some other upward vertical force is applied (perhaps by a helium balloon), the book is going to slide.

The ‘person holding a book against the wall’ is a classic introductory physics problem. One hopes a student preparing for the AP Physics C came to a stop and scratched their head when coming across this version. A well prepared student should know it’s screwed up.

What about the other questions? Some of the other questions at that practice site were ok, but in my opinion, often not “AP Physics C like”. For example:

• I saw questions that required unit conversion and/or required kids to know the meaning of prefixes in SI. Kids should know how to do unit conversions andwhat “c”, “m”, “K” and so on mean. However, the number of conversions on the AP Physics C exam range from none to almost none with none seeming the more frequent situation; the same goes for use of “c”, “m” and so on. So: not as AP Phys C like as they should be.
• At least one question seemed physically odd to me. For example: there was one about a mouse walking in toward the central axis of a spinning turntable. The intention was to use conservation of angular momentum. I grew up with turntables. We still own one. I’m pretty sure torque is always applied to real turntables when they are spinning. Perhaps this is ok for students who never saw a turntable and have no idea how they work and who likely recognizes the intention is to test whether they know how to apply conservation of angular momentum. But the College Board usually avoids questions where the real situation doesn’t conform to the assumptions the student is supposed to make.
• Some questions were ill-posed. One asked the student to compute the coefficient of friction of a car with known speed taking a turn around a circle of known radius. However, the question did not say that the speed was the maximum possible speed. So, technically, the correct answer should be “not enough information”. As worded there is only enough information to find the lower bound on the coefficient of static friction. Based on the information given, it could be infinite. (But it’s multiple choice so a student will probably get the answer the question writer was seeking. Still…. Knowing that the formula for computing static friction is an inequality is a very important point the AP Physics C tests. So: bad question that has the potential for feeding a misconception.)

That said: the site is free, and most questions were mostly ok. In my opinion, they are not not especially useful for testing how well you’d do on the AP Physics C exam. Since many resources exist, I would not send a student prepping for the AP Phys C test to that site. Other resources are a better use of their time.

Like what? I would advise that student to find old AP Physics C exams written by the College Board. Those who hang out at reddit can find plenty.

I’ve been trying to make tweaked practice questions for the AP Physics 2 test. To gauge the ‘types’ of questions, I downloaded the six practice questions they provide in AP Physics 1 & 2 Sample questions. I got a kick out of this question. Why? Read the learning objective.

Do you see a “moving fluid” here? I don’t.

Generally speaking, I’d put this under a learning objective for “the hydrostatic equation” which makes the physics more straightforward. That said: the fact they put this under “Bernouilli’s equation would seem to explain why none of the 143 (to my count) learning objectives says “motionless fluid” or “hydrostatic equation”.

JD Ohio is trying to advise his son whether to take AP Physics 1 or “regular” physics at his school next year and asked for help. It’s a bit difficult to advise– because among other things, the content of “regular” physics classes varies widely at different schools. It isn’t always easier than AP Physics 1 — it depends on the teacher and their notions about how to grade and so on. One “up” side for AP Physics 1 is the potential for a student to get college credit. (I’ll defer discussing whether they should use the credit or retake physics for a later time; the answer is “It depends”.) The difficulty with this “up” side is “pass” rate on the AP Physics 1 test is horrifically low. Generally speaking schools will require a 5 o 4 for credit. Here’s the pass rate:

(Update: The left hand column of numbers are the % who earned a 5; the far right column is the % who earned a 1.)

That said: if a kid does get a 4 or 5 on the AP Physics 1 some schools may weight that outcome very favorably for admissions or merit scholarships. But I can’t say this for sure. Large state schools often have rather mechanical admissions criterion and may only look at the grade his teacher recorded. This is a factor to consider if the high school teacher gives out only 4% A to reflect the “pass” rate on the test.

So far, you can see the answer about whether your son should take AP Physics 1 is “It depends. Before your son makes his choice, I recommend two things.

Recommendation 1: Get info from the school and compare the classes.

• Obtain and compare the physics syllabi for the two competing physics classes at his school. Oddly, sometimes the “traditional” physics is no easier than AP.
• Ask for the distribution of 1-5 scores on the AP 1 test for kids from 2015 and 2016 without student names of course. You just want statistics. (Don’t ask for results of the 2014 test. It didn’t exist.)
• Ask for the distribution of A-F scores given by the AP 1 and traditional physics classes for the past two school years. Once again: just ask for statistics.

Obviously, if the fraction of kids who get scores of 4-5 at your school is <2% you really can't expect your kid to get a 5. Or at least you can't expect him to get it based on the class taught at that high school. Also, if the AP 1 class is a GPA buster and no one gets 4-5 scores on the AP 1, I suggest a student keep away from that class. On the other hand: if the school gives a higher fraction of A’s in the AP class– and this sometimes happens, maybe have him take it anyway.

You may or may not find schools willing to give you this info. It may or may not exist.

I think a high school should have a syllabus of these on file– I think they are required accreditation. If they claim they don’t have one or have some policy against giving it to you — and some schools are like that– if your child is in a public school you can either threaten to FOIA and or actually FOIA. No matter what policy they want to have this information is subject to FOIA. It depends how pugnacious you want to be. Maybe just sigh, “Well… I guess I may need to FOIA.” Seriously.

On the other hand, it may actually possible they don’t keep a list of statistics with distribution of student outcomes on AP tests; I don’t know if accreditation agencies require schools to supply this. If the school does create a list and have it on file, that should be available using FOIA. You can always ask. ( Of course, one might want to achieve the outcome of filing the FOIA without having the school know they were the one to make the request. You might want to get a relative with a different last name to file FOIA. 🙂 )

Recommendation 2: Learn a little physics in a low stakes way the summer before he takes it in High School.
For what it’s worth, this advice is useful if he takes traditional physics as well. No matter what the teacher covers we can be fairly sure that unless the teacher is q_u_i_t_e s_l_o_w (which is generally a bad thing ) the teacher will probably include the following topics in both classes.

(1) Linear kinematics with trig. (This is called “straight line motion” )
(2) Newton’s 1-3 with discussion of various forces: weight, friction, springs, and tension.
(3) Conservation of Momentum & Impulse Momentum. (If they do both, they will call it the latter.)
(4) Work-energy.
(5) Circular motion. (AP 1 should also cover “Rotational motion” which a bit more. Oddly, they don’t cover rotational *statics*. Why ask why?)
(6) Newton’s law of Universal Gravitation.
(7) Charge, current and analysis of resistive circuits.

Other topics will generally also be covered. For example: AP 1 should cover “waves-harmonic motion” but no other topics because they aren’t on the test. Traditional physics may cover “geometric optics” and include more electro-statics than AP 1; it may cover magnetism. The AP curriculum leaves some of these to the AP 2 or AP C class. They are not in AP 1.

So: How can he study in the summer?

Udacity’s “https://www.udacity.com/course/intro-to-physics–ph100” covers a fair number of the topics at a “intro” level that is suitable for pre-AP1 or pre-high school physics. Udacity claims their course is at the college level– but that’s only true if you mean “Physics for non-science majors”. AP 1 is a bit more like “physics for biology/premed etc.” If you scan Udacity lessons, none called after their ‘physics’ name which makes it hard for someone who doesn’t know physics to determine how it relates to AP Phys 1.

The Udacity class is free and self paced; they estimate the class takes 2 months. This is doable and about the right amount of calendar time to budget. If a student sets aside regular time in summer, they’ll find these sort of get them up to the level that is already a “C” in many high school classes before the semester started. They’d probably forget as the semester wear on, which is ok. They’ll find the “re-introduction” easier than otherwise. Plus given the range of current pedagogical practices, having seen demonstration of how to do the “plug and chug” an immense help. Kids often find kinematics confusing for various reasons which are often a blend of conceptual and “plug and chug” issues.

Here’s what in the Udacity course– translated into physics topic terminology:

• Lesson 1 is “Trig & Error Analysis”. The trig is restricted to the small amount you need for physics. (Note: The AP 1 score distribution mentions “Multiple-choice questions on Science Practice 5 (Data Analysis & Evaluation) posed the greatest challenge to students.” The intro to “error analysis” might help here.)
• Lesson 2 is “Linear Kinematics” which is done with some trig. This basis if done before class starts can really help students.
• Lesson 3 is “Newton’s 1-3”.
• Lesson 4 is “Work-Energy”.
• Lesson 5 is “Harmonic Motion”. (Note above, students who took the AP 1 were weak on this. Possibly this is because it is done near the end of the course and teachers end up rushed. Also: to some extent, harmonic motion done using algebraic methods is– in my view– more difficult that done using calculus. I had a student who knew calculus and differential equations “get it” when I showed her the “calculus way”. )
• Lesson 6 is “Electricity”. ( Which doesn’t quite match the way the AP 1 does it because the AP 1 does it in a funny sort of way.)
• Lesson 7 is “Special Relativity”. This is not on the AP 1; it’s not included in many algebra based physics classes. This is sometimes covered in “Conceptual Physics” classes- that is the ones that are considered “easier physics”. If the students goal is to get up to speed for their introductory physics class, this will usually be a waste of time. On the other hand, if they want to learn it, it’s sort of fun.

The way the Udacity ‘classes’ run, the student pretty much launches a video. The video will have some explanations, show some methods to apply concepts in equation form, make the student apply the equations and fill in a “blank” to get some practice. The student finishes the video and then works problems– once again by video. The total number of required problems is light. They can take tests also. Obviously, if a student is merely trying to get familiar for the upcoming semester, they should not stress about perfection, but just try to be familiar with material.

The purpose of the summer work is to benefit from something called “spacing”. (He can also benefit from the “retrieval effect” by giving himself some low stakes tests to test his retention to test himself. To do this, he could take a re-test on Lesson 1 sometime around when he is doing Lesson 3. Spacing and retrieval are very powerful but difficult for kids to ‘add in’ during the school year because they have too much “fire-hose/cramming” stuff going on.)

Is there anything else?
I can hunt around for other good “pre-Physics” MOOC’s. Kids scattered around the country would probably benefit from “pre-Physics MOOCs” but that doesn’t mean there is any demand. So they may not exist. Most the MOOC I’ve found are for AP Physics C which attract kids who are focused on the challenge of “passing a test”.

There are are a lot of good videos by Hewitt that would be useful for “pre-Physics” (and also as explanations when a student just doesn’t get a concept during their AP 1 class). But as far as I am aware, unlike the Udacity MOOC, these aren’t put together with questions for the student to test their understanding even at the most superficial level. So I can’t currently recommend something for kids who want to “get a head start” to do with them.

Anyway, I hope this helps. If it doesn’t help you, perhaps it will help other parents who are trying to make an appropriate choice.

As I tutor physics, I often find students who are puzzled by experiments they were exposed to in class. Today’s she found herself confused by precisely what went on during a classic “electroscope” lab. She could describe the observations but she said she knew she didn’t understand precisely what was going on with the electron flow.

I knew I could explain the results to her, try to sketching things out and so on. Lucky for me and her, I was aware of something even better. A great video on inductive charging of an electroscope. Here it is:

Now I know some of you are going to say, “How can that be great? The scope is just an ugly bent hanger! There aren’t any equations. It isn’t cool, cutting edge. That would never make it into a NOVA like special. Blah. Blah.”

But I’ve shown this to several students who were puzzled about electroscopes, and it really gave them an “A Ha!” and an “Oh wow! Now I get it.” Also: the video is short, doesn’t digress into lots of other things; the electroscope may not be pretty but it is real (not a cartoon). The student did make me stop at one point where she was confused and I could show her precisely how the flow of electrons was illustrated by the guy’s super-imposed +/- signs and we could scroll back a bit.

Students always love the good videos if seen at just the right time.

Many ask how I find the ones I do find because they report that they sometimes look and hunting for useful videos — sometimes they hunt because their teacher suggests there are good ones “out there” without pointing to anything in particular. But they find hunting is just a time sink that never results in good ones.

In fact today’s student asked me how I find good ones and I told her: I spent quite a bit of time looking for the ones that are good and beyond that, I know what it is the teacher is trying to get them to grasp. So, I look for videos that focus on those topics. I would never tell a student who is trying to learn to actually look for a video themselves. It takes a long time to find the ones that actually help on the topic the student is trying to better understand in the time frame they need for their course.

I have a few more great videos I’ve found and I’ll be showing them from time to time. (There’s a great one out there showing standing waves and a few fun ones on the Doppler effect.) If anyone happens to know of great physics videos, I’d love to see links.

Mind you: what you think is “great” may not be what I think is great. 🙂 For helping kids with a concept videos generally need to be less than 10 minutes; ideally, it should be less than 5 minutes long. Half-hour or hour-long videos may be good lecture replacements but they are rarely (as in almost never) helpful to a student who has a specific question about a concept they are trying to master. That said: there are some good “lecture replacement” videos. It’s just that students rarely need them– they already have lectures or classroom activities. But if you think you’ve found a great video of any sort, let me know.

Is this an open thread: Yep. 🙂
Update 1/27/2017: For convenience, I’m moving political discussion to the following post which describes a Trump strategy on the ACE.

On a non-political note. Many of you know I’ve been tutoring physics (which is fun.) I find lots of parents ask me if I know of any chemistry or math tutors. I decided early on to stick to one area because it’s more efficient to have a bunch of high school physics students rather than a kid in algebra, another in trig, another in geometry, another in physics and so on. So my answer is I don’t do chemistry, math or any of those things. (I’ve answered easy math questions in a pinch. Calculus– no problem. But don’t ask me to do synthetic division!)

That said, I’d like to have a personal list of tutors so I could give contact names to parents who would then be responsible for doing things like calling references and so on. (I’ve actually started a list putting something on a neighborhood forum.)

If anyone is or knows of a good Chemistry or Math tutor in the DuPage Co. Illinois area, I’d love to meet them. Heck, I get full enough I might need to know some Physics tutors to give out as names. FWIW…. any science or programming tutors. I’ve had parents ask me for tutors in C programming.

(Those wondering: Why not advise parents or students to contact any of the zillions of tutoring services? Those services tend to charge parents two to three times what the tutor is paid. Also, their tutors tend to be private contractors. So if a consumer can generally get exactly the same tutor if they know how to find them. And, there’s lots of room for price savings between the amount asked by the service and paid to the tutor. So, I know I’d like to be able to give out a list of name to parents (or even get together and meet people for drinks or coffee sometime.)

Anyway, open thread. But keep the DNC/GOP/TRUMP/HRC stuff on the other threads!

Ok. I’m feeling pretty stupid. This should be simple. Is this ambiguous, or is it just me?

A long,straight wire carries a current of 740 mA. A thin metal rod 45 cm long is oriented perpendicular to the wire and moves with a speed of 1.8 m/s in a direction parallel to the wire. What are the size and direction of the emf induced in the rod if the nearest point of the rod is 3.5 cm away from the wire, and if the rod moves in a direction parallel to the current?

I keep reading and reading. I drew two geometries both of which seem to match what the problem says. I show them below. (I chose to make the “thin” rod as circular. It’s probably flat, but that’s not really my question.) Can any of you point to anything in the problem statement that makes it clear they mean one, the other, or something entirely different?

Interpretation 1.	Interpretation 2.
Metal rod perpendicular to wire? Yes. Moving parallel to wire? Yes. Nearest point 3.5 cm away? Yes. Middle of rod is is above the wire. Moving parallel to current? Yes.	Metal rod perpendicular to wire? Yes. Moving parallel to wire? Yes. Nearest point 3.5 cm away.Yes. Left edge of rod is to right of wire. Moving parallel to current? Yes.

Both geometries seem like decent AP Physics C level problems. They just aren’t the same problem.

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Update for Mark

I’ve been trying to gin up good moodle based problems for my tutees– which is why I’m discussing “teaching” instead of topics of greater interest to many of the visitors. In comments thread of a previous post, I mentioned that I’d seen yet another problem that seemed rather physically unrealistic. In particular, I mentioned what appeared to be an implausible food drop. My memory was close, but not quite right. I now have a screenshot of the problem!

Like the problem of the kid flinging flowers on to the balcony, this “unrealistic drop” also contains what I consider a sub-optimal image that (a) doesn’t help the student visualize the features required to solve the problem and (b) presents a degree of cognitive dissonance. Perhaps perfect images are not important, but then there the question itself The the values of the knows! Oh the values….!

Of course I’ll let you judge for yourselves. Here is as it is presented to a student (with the answer obliterated):

Note: If we go by the image, in this problem the propeller driven aircraft flying at 257 m/s is dropping “emergency food supplies”. (My recollection when I previously reported this was faulty. I recalled a slower aircraft. 🙂 )

Now for the oddities that can make one think “huh?” Maybe not “that’s impossible”, but still “huh”?

1. 257 m/s corresponds to a speed of 575 mph. This speed is achievable by a bomber or a commercial jet The “Russian Bear” is propeller driven and can also fly this fast. That said: I’m not sure whether the Russians would use a Russian Bear to drop “emergency food supplies”. I imagine someone dropping “emergency food supplies” would want fly a bit slower if they could. (Or maybe that’s just me.)
2. In the image, the package appears to have a parachute attached. Despite the presence of the parachute, I suspect the ‘correct solution’ requires students to neglect drag. Mind you, this is high school physics, so the students wouldn’t know how to deal with drag when it’s important.

   Still: Why use a picture that suggests that ‘neglect drag’ would be incorrect? My answer: one should avoid choosing an illustration that communicate notion that an assumption students are expected to make would be incorrect. To avoid cognitive dissonance for students who might have experienced “aerodynamic drag” when sticking their hand out a car window or who might be familiar with the existence and purpose of parachutes: don’t ‘sex up’ questions that require them to neglect drag with pictures that include parachutes.

3. But I have even greater cognitive dissonance when I solve the problem neglecting drag. If there were no drag and the package was dropped from 1.4 km, these supplies will hit the ground with a speed of ~306 m/s (i.2. sqrt(257^2+2*9.8*1400), Mach 0.9, 816 mph). While it’s not impossible for dropped objects to achieve such speeds, I can’t help but worry about the integrity of the packaging. Can a wooden crate hitting the ground with that speed survive impact? What are these “emergency food supplies packed in? Real questions.

   On the one hand, I don’t necessarily expect students to think about this. But in reality we actually do want them to ‘reality check’ their answers. In this case, the supposedly “correct” answer forces one to conclude “The person who organized this drop is a blithering idiot.”

Of course some of the questions that make one think “huh” go away if (a) the parachute is removed from the image and the (b) “emergency food supplies” are a bomb. In those cases drag might be modest relative to gravity and we don’t want the bomb to survive an impact with the ground. Perhaps this question was merely ‘converted’ by substituting “emergency food supplies” for “bomb”. That’s not a very good excuse for not changing the numbers to something reasonable, but it might explain the magnitudes that make one go “huh”?

But as DeWitt previously observed

lucia,

They could have said a bomb instead of a package, but that would be non-PC. Bombs are dense enough that ignoring air resistance is a reasonable assumption. That speed is about right for a small plane. A Piper Cub couldn’t go even that fast, top speed 137 km/hr. The cruising speed of a Japanese WWII Betty bomber was 315km/hr at 3km altitude.

The solution to that problem is why the atom bombs dropped on Japan had parachutes attached.

Yep. Even bombs often have parachutes attached.

All in all, I can’t help thinking: Why the heck not adjust the numbers to suggest the “emergency food supplies” are being dropped by a guy flying an old fashioned crop duster? Why not have supplies dropped from something that can fly lowish and slowish? I suspect the answer is “Numbers were spit out by a random number generator programmed with little thought about realistic choices.”

Mind you: This sort of question remains a good exercise in the sense the student learns or is tested on the procedure for solving problems in projectile motion. But it’s sub-optima if we hope for the side effect of student’s a sense of what might really work in the real world.

That said, I don’t actually mind unrealistic problems. When I want students to learn the process, I prefer full on “unrealistic” and do this:

(Actually, I’m thinking of moving the base camp to 50 m/s and increasing the ‘hover velocity’. I have no idea what the minimum ‘hover velocity’ would be for an alien space craft, but I’d like to change the values to would ensure students who forgot horizontal velocity when computing the answer to (9) would get a different result from those who remembered to include it. )

As I mentioned before: There’s a good reason Wil E. Coyote and Road Runner appear in many projectile motion problems!

I thought Mark Bofill might enjoy this physics problem which was actually assigned to one of my students. I’m showing it exactly as presented to the student (though reduced in size.)

As a rather minor comment, I’d like to point out the image inserted is merely “decorative”. Nothing in the image clarifies the question (which is, btw, repeated both before and after the image). Also, I know from experience that some students view these questions on smallish screens (iPads.) The inclusion of the images means they read the question and then need to scroll down to the answer box. Now, one might say the need to scroll is a “first world problem”, but I would also suggest that inclusion of the image is both needless and, if anything, counter productive. But that’s just me.

Now for the bit that makes me think Mark Bofill will enjoy this. Recall previously after reading the text of a problem that appeared on the DuPage county Regional Office of Education physics tests, Mark commented:

This doesn’t really pertain directly, but it was nagging at me. The initial problem with the child accelerating the wagon would seem to require a child of unusual athletic talent. Kid needs to be in contact with the wagon for the three seconds to be applying the force, so at the end that kid is cooking along at 15 m/s too.

Adults don’t really sprint faster than 12 m/s.

Based on that thought he might enjoy the solution to this problem. I’m squinting, but the relevant part of the text appears to read:

“A boy throws a small bundle of flowers toward his girlfriend on a balcony 11.1 m above him. The bundle stopped rising after 2.61 s.

How high did the bundle travel?”

The answer to this is to first ‘know’ that a bundle of flowers should be modeled as an ideal projectile (i.e. no drag on the fluffy decorative fronds). Then recognize the bundle of flowers has zero velocity at the top of the trajectory, and know the distance traveled up is the same as the distance it would take for it to fall down from that height. In this case: H = 0.5* 9.8 m/s² (2.41 s) ².

The answer is: H = 33.37929 m. Which is 109 ft.

What speed did he through these at? Assuming he toss them straight upV= 9.8 m/s² * 2.41 s 25.6 m/s ~ 52.832 mph.
I’m know professional baseball pitchers can throw 80 mph. But really… Romeo tossing a bundle of flowers at 57 mph? Which is fast enough to vault three times the height of the balcony? Thank heaven there really would be drag otherwise the minimum velocity when those flowers fall back down on Juliet is 20.9 m/s (46.7 mph.) She better dodge those and let them splat on the balcony!

FWIW: I actually grabbed a bunch of sedum with nice fluffy flower heads on it and tried to toss one straight up. I couldn’t get more than 12 feet. So I asked my burly neighbor. He maybe got 15-16 feet. We tried straight up, a bit of an angle and so on. We didn’t try to make a bundle and optimize the shape or weight to make the flowers more throw-able.

I have to admit I’ve written similarly unrealistic problems using Moodle’s random number generator. (I later learned to write an R script to attempt to avoid having roller coasters fall off their tracks at the top of the “loop-de-loop”, or kill passengers from excess ‘g’ forces.) But trying to write problems that meet all the rules of ‘optimum’ why I prefer to use “super ninja” when writing physics problems.

Of course Super Ninja will do things no mere mortal can do. But I can at least write problems where students don’t can minimize need for a calculator, reduce challenges of entering numerous digits in the ‘moodle’ entry box and so on. With Super Ninja, a student with a sense of what is physically plausible won’t hesitate over the answer because it violates their sense of what could even happen: after all, this is “super ninja”.

Did you ever wonder why there were so may problems with “Wiley Coyote” and “Road Runner”? I’m pretty sure this is why. Possibly the boy in question here is “super boy” who lives on “airless planet X” which looks just like earth and whose local acceleration due to gravity the student is supposed to just know. Or something.